BER Research Highlights

Search Date: September 18, 2020

53 Records match the search term(s):


December 29, 2018

Temperature Dependence of Plant Photosynthesis at the Global Scale

Researchers used a large global dataset to develop new insight into the temperature response of photosynthesis.

The Science
An international team of ecologists developed a robust, quantitative global model that represents the acclimation and adaptation of the photosynthetic temperature response. The model is capable of predicting observed global variation in the response of photosynthesis to temperature, enabling improved prediction of global ecosystem response to a warming climate.

The Impact
To predict the response of ecosystems to a warming planet, it is critical to understand—and model—the response of photosynthesis to temperature. This study used a large global dataset ranging from the Arctic to the tropics to gain important new understanding and develop a model capable of predicting the response of photosynthesis to temperature across the planet.

Summary
To predict the response of ecosystems to a warming planet, it is critical to understand—and represent in models—the response of photosynthesis to temperature. An international research team developed new mathematical functions to represent the photosynthetic temperature response in terrestrial biosphere models (TBMs) to account for both acclimation to growth temperature and adaptation to climate of origin, using a global database that contains more than 140 species. They found acclimation to growth temperature to be the principal driver of the photosynthetic temperature response, and they observed only a few modest effects of adaptation to temperature at the climate of origin. The observed variation of temperature optimum for leaf net photosynthesis was primarily explained by the photosynthetic biochemical component processes rather than stomatal or respiratory processes. The new temperature response functions presented in this study capture the observed temperature optima across biomes with higher degree of accuracy than previously proposed algorithms and span a much larger range of growth temperature.

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Climate and Environmental Sciences Division (SC-23.1)
Terrestrial Ecosystem Science
daniel.stover@science.doe.gov

Principal Investigator
Alistair Rogers (prepared highlight on behalf of other BER co-authors)
Brookhaven National Laboratory
Upton, NY 11973-5000
arogers@bnl.gov

Note that this research was led by the University of Western Sydney, Australia. Scientists sponsored by the Office of Biological and Environmental Research within the U.S. Department of Energy’s (DOE) Office of Science contributed to the dataset used in the study and include Alistair Rogers [Next-Generation Ecosystem Experiments (NGEE)–Arctic), Jeff Chambers (NGEE–Tropics], Jeff Warren [Spruce and Peatland Responses Under Changing Environments (SPRUCE)], and Molly Cavaleri (DE-SC0012000).

Funding
This research was supported by a Western Sydney University Ph.D. scholarship to DK. AR  was supported by the Next-Generation Ecosystem Experiments (NGEE)–Arctic project, which is funded by the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy (DOE) Office of Science, through contract number DE-SC0012704 to Brookhaven National Laboratory (BNL). KYC was supported by an Australian Research Council DECRA (DE160101484). DAW acknowledges a Natural Sciences and Engineering Research Council (NSERC) of Canada Discovery grant and funding from the Hawkesbury Institute Research Exchange Program. JU, LT, and GW were supported by the Swedish strategic research area Biodiversity and Ecosystem Services in a Changing Climate (BECC; www.becc.lu.se). JQC was supported by the NGEE–Tropics project, which is funded by DOE BER. MDK was supported by the Australian Research Council Centre of Excellence for Climate Extremes (CE170100023). MS was supported by an Earl S. Tupper postdoctoral fellowship. AMJ and JMW were supported by DOE BER under Contract No. DEAC05-00OR22725. MAC was supported by DOE grant DE- 705 SC-0011806 and the U.S. Department of Agriculture Forest Service 13-JV-11120101-03. Several of the Eucalyptus datasets included in this study were supported by the Australian Commonwealth Department of the Environment or Department of Agriculture, and the Australian Research Council (including DP140103415).

Publication
Karamathuge, D. P., B. E. Medlyn, J. E. Drake, M. G. Tjoelker, M. J. Aspinwall, M. Battaglia, F. J. Cano, K. R. Carter, M. A. Cavaleri, L. A. Cernusak, J. Q. Chambers, K. Y. Crous, M. G. De Kauwe, D. N. Dillaway, E. Dreyer, D. S. Ellsworth, O. Ghannoum, Q. Han, K. Hikosaka, A. M. Jensen, J. W. G. Kelly, E. L. Kruger, L. M. Mercado, Y. Onoda, P. B. Reich, A. Rogers, M. Slot, N. G. Smith, L. Tarvainen, D. T. Tissue, H. F. Togashi, E. S. Tribuzy, J. Uddling, A. Varhammar, G. Wallin, J. M. Warren, and D. A. Way. “Acclimation and adaptation components of the temperature dependence of plant photosynthesis at the global scale.” New Phytologist 222(2), 768–84 (2019). [DOI:10.1111/nph.15668]

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


December 18, 2018

Homeostasis of Tropical Forest Carbohydrates

The Science
Through the most exhaustive tropical forest carbohydrate sampling and analysis done to date, researchers found that canopy tree carbohydrate concentrations are insensitive to both seasonal drought and long-term climate. They also identified easily measured traits that may be predictive of carbohydrate concentrations.

The Impact
These findings help to unify the understanding of forest carbohydrate dynamics across the few existing tropical datasets. Since carbohydrates play an important role in forest survival, this may improve the ability to simulate vegetation dynamics in Earth System Models (ESMs), and trait relationships should simplify model benchmarking.

Summary
Non-structural carbohydrates (NSCs), the organic compounds that drive plant metabolism, have rarely been studied in moist tropical forests, so their regulation in these systems is poorly understood. These compounds may modulate tree drought response and can become depleted if demand (i.e., growth, defense, respiration) exceeds supply (i.e., photosynthesis). As a result, ESMs rely on carbohydrates as a metric for vegetation survival. Researchers from the Next-Generation Ecosystem Experiments (NGEE)–Tropics project measured foliar and branch NSCs of 23 canopy tree species across a large precipitation gradient in Panama during the 2015–2016 El Niño drought to examine how short- and long-term climatic variation impacts carbohydrate dynamics. There was large variation in NSCs across species; however, there was no change in total NSCs as the drought progressed or across the rainfall gradient. Some NSC variation could be explained by easily and ubiquitously measured traits, providing potential for improved model benchmarking. These findings suggest that NSCs are an allocation priority in moist tropical forests and should improve the ability to capture vegetation dynamics in ESMs.

Contacts
BER Program Managers
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov

Dorothy Koch
SC-23.1
Dorothy.Koch@science.doe.gov

Principal Investigators
Chonggang Xu
Los Alamos National Laboratory
Los Alamos, NM 87545
cxu@lanl.gov

Nate McDowell
Pacific Northwest National Laboratory
Richland, WA 99354
nate.mcdowell@pnnl.gov

Funding
This work was supported by the Next-Generation Ecosystem Experiments (NGEE)–Tropics project, funded by the Office of Biological and Environmental Research within the U.S. Department of Energy Office of Science.

Publications
Dickman, L.T., N.G. McDowell, C. Grossiord, A.D. Collins, B.T. Wolfe, M. Detto, S.J. Wright, J.A. Medina-Vega, D. Goodsman, A. Rogers, S.P. Serbin, J. Wu, K.S. Ely, S.T. Michaletz, C. Xu, L. Kueppers, and  J.Q. Chambers. “Homeostatic maintenance of non-structural carbohydrates during the 2015-2016 El Nino drought across a tropical forest precipitation gradient.” Plant, Cell & Environment 42(5),1705–1714 (2018). [DOI:10.1111/pce.13501]

Related Links
https://ngt-data.lbl.gov/dois/

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


December 17, 2018

Influence of Dual Nitrogen and Phosphorus Additions on Nutrient Uptake and Saturation Kinetics in a Forested Headwater Stream

Coupled nitrogen and phosphorus dynamics in a forested headwater stream.

The Science
Scientists at Oak Ridge National Laboratory (ORNL) examined the effects of single and dual nitrogen and phosphorus additions on nutrient cycling in a co-limited (i.e., for nitrogenand phosphorus) headwater stream (Walker Branch, Tenn.).

The Impact
There is a growing need to investigate coupled biogeochemical cycles, especially in ecosystems that may be co-limited (e.g., for nitrogen and phosphorus). This novel research approach used two nutrient addition techniques to investigate coupled nitrogen and phosphorus cycling in stream reaches and may be applied to other elemental cycles and environmental settings.

Summary
Nitrogen and phosphorus can limit autotrophic and heterotrophic metabolism in lotic ecosystems, yet most studies that evaluate biotic responses to colimitation focus on patch-scale (e.g., nutrient diffusing substrata) rather than stream-scale responses. In this study, ORNL scientists evaluated the effects of single and dual nitrogen and phosphorus additions on ambient nutrient uptake rates and saturation kinetics during two biologically contrasting seasons (spring and autumn) in Walker Branch, a temperate forested headwater stream in Tennessee, USA. In each season, they used separate instantaneous pulse additions to quantify nutrient uptake rates and saturation kinetics of nitrogen (nitrate) and phosphorus (phosphate). The team then used steady-state injections to elevate background stream water concentrations (to low and then high background concentrations) of one nutrient (e.g., nitrogen) and released instantaneous pulses of the other nutrient (e.g., phosphorus). The researchers predicted that elevating the background concentration of one nutrient would result in a lower ambient uptake length and a higher maximum areal uptake rate of the other nutrient in this co-limited stream. Their prediction held true in spring, as maximum areal uptake rate of nitrogen increased with elevated phosphorus concentrations from 185 µg m2 min1 (no added phosphorus) to 354 µg m2 min1 (high phosphorus). This pattern was not observed in autumn, as uptake rates of nitrogen were not measurable when phosphorus was elevated. Further, elevating background nitrogen concentration in either season did not significantly increase phosphorus uptake rates, likely because adsorption rather than biotic uptake dominated phosphorus dynamics. Laboratory phosphorus sorption assays demonstrated that Walker Branch sediments had a high adsorption capacity and were likely a sink for phosphorus during most pulse nutrient additions. Therefore, it may be difficult to use coupled pulse nutrient additions to evaluate biotic uptake of nitrogen and phosphorus in streams with strong phosphorus adsorption potential. Future efforts should use dual nutrient addition techniques to investigate reach-scale coupled biogeochemical cycles [C-N-P, and other elemental cycles, such as iron (Fe), molybdenum (Mo)] across seasons, biomes, and land-use types and over longer time periods.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov

Principal Investigator
Natalie A. Griffiths
Oak Ridge National Laboratory
Oak Ridge, TN 37831
griffithsna@ornl.gov

Funding
This research was part of the long-term Walker Branch Watershed project at Oak Ridge National Laboratory (ORNL) and supported by the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy (DOE) Office of Science. ORNL is managed by UT-Battelle, LLC, for DOE under Contract No. DE-AC05-00OR22725. Appreciation is extended to T.V. Royer for partial laboratory support and to Indiana University’s School of Public and Environmental Affairs for supporting LTJ’s time.

Publications
Griffiths, N.A., and L.T Johnson. “Influence of dual nitrogen and phosphorus additions on nutrient uptake and saturation kinetics in a forested headwater stream.” Freshwater Science 37(4), 810–825 (2018). [DOI:10.1086/700700]

Data citation: Griffiths, N.A., and L.T. Johnson. 2018. Walker Branch Watershed: Effect of Dual Nitrogen and Phosphorus Additions on Nutrient Uptake and Saturation Kinetics, 2011–2012. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee, U.S.A. [DOI:10.25581/ornlsfa.015/1484490]

Related Links
Data are available on the ORNL TES SFA website: https://tes-sfa.ornl.gov/node/80#WBW_new

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


December 06, 2018

Methane Production and Emissions in Trees and Forests

Trees are overlooked sources and sinks in global forest methane budgets.

The Science   
Scientists have only recently understood that trees can emit or consume methane from the atmosphere. This is the first comprehensive review of the literature on trees and forests as methane sources and sinks.

The Impact
Until recently it was assumed that all exchange of methane between forests and the atmosphere takes place at the soil surface. This review demonstrates that all surfaces in a forest—living wood, dead wood, leaves, branches, and epiphytes—can exchange methane, a fact that will change this study's approach to building forest methane budgets.

Summary
Forest ecosystem methane (CH4) research has focused on soils, but trees are also important sources and sinks in forest CH4 budgets. Living and dead trees transport and emit CH4 produced in soils; living trees and dead wood emit CH4 produced inside trees by microorganisms; and trees produce CH4 through an abiotic photochemical process. Here, researchers review the state of the science on the production, consumption, transport, and emission of CH4 by living and dead trees, and the spatial and temporal dynamics of these processes across hydrologic gradients inclusive of wetland and upland ecosystems. Emerging research demonstrates that tree CH4 emissions can significantly increase the source strength of wetland forests, and modestly decrease the sink strength of upland forests. Scaling from stem or leaf measurements to trees or forests is limited by knowledge of the mechanisms by which trees transport soil-produced CH4, microbial processes that produce and oxidize CH4 inside trees, a lack of mechanistic models, the diffuse nature of forest CH4 fluxes, complex overlap between sources and sinks, and extreme variation across individuals. Understanding the complex processes that regulate CH4 source-sink dynamics in trees and forests requires cross-disciplinary research and new conceptual models that transcend the traditional binary classification of wetland versus upland forest.

Contacts
BER Program Manager
Daniel Stover
SC-23.1
Terrestrial Ecosystem Science
Daniel.Stover@science.doe.gov

Principal Investigator
Pat Megonigal
Smithsonian Environmental Research Center
Edgewater, MD 21037-0028
megonigalp@si.edu

Funding
Funded by a grant to J. Patrick Megonigal by the Terrestrial Ecosystem Science (TES) program of the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy (DOE) Office of Science, titled Sources, Sinks and Processes Regulating Cryptic Methane Emissions from Upland Ecosystems (DE-SC0008165) and the Smithsonian Institution.

Publications
Covey, K.R., and J.P. Megonigal. “Methane production and emissions in trees and forests.” New Phytologist 222(1), 35–51 (2019). [DOI:10.1111/nph.15624]

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


December 06, 2018

Soil Minerals Reduce Phosphorus Availability

Association of phosphorus to soil minerals limits nutrient availability in tropical soils.

The Science
Phosphorus is a limiting nutrient in tropical soils, in part because of its tendency to associate strongly with soil minerals. Phosphorus-soil associations were measured on tropical soils from around the globe and were associated with high clay content.

The Impact
Phosphorus associates strongly with soil minerals, particularly clays, providing an important constraint on its availability to plants and microbes. Very high phosphorus concentrations were needed to confidently determine the strength of its association with soil minerals.

Summary
Very high phosphorus concentrations are needed to quantify association with soil minerals in tropical environments. Studies that aim to quantify this association typically do not use tropical soils, even though phosphorus is a key limiting nutrient in the tropics. Many studies use phosphorus concentrations that are too low to yield confidence in the parameters for the Langmuir equation that describe phosphorus attachment. This study provides specific recommendations for quantifying phosphorus associations with tropical soil minerals. 

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Climate and Environmental Sciences Division (SC-23.1)
Terrestrial Ecosystem Science
daniel.stover@science.doe.gov

Principal Investigator
Melanie Mayes
Oak Ridge National Laboratory
Oak Ridge, TN 37831
mayesma@ornl.gov

Funding
This research was supported as part of the Next-Generation Ecosystem Experiments (NGEE)–Tropics project, funded by the Office of Biological and Environmental Research within the U.S. Department of Energy Office of Science.

Publications
Brenner, J., et al. “Phosphorus sorption on tropical soils with relevance to Earth system model needs.” Soil Research 57(1), 17–27 (2019). [DOI:10.1071/SR18197]

Related Links
Dataset: DOI:10.15486/ngt/1434046

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


November 20, 2018

Near-Future Forest Vulnerability to Drought and Fire Varies Across the Western United States

Vulnerability highest in the Southwest and Sierra Nevada, lowest in the Pacific Northwest, U.S.

The Science
The study assessed forest vulnerability to drought and fire across the western United States during 2020–2049 using the Community Land Model (CLM4.5), which simulates forest growth and wildland fire given prescribed climate conditions. Researchers used future climate conditions that are based on the current trajectory of greenhouse gas emissions. Defining multiple forest types and environmental and climate conditions at a fine spatial resolution, regionally relevant fire fuel limits, and enhanced tree response to drought were important model improvements. The improved model allowed the researchers to assess the potential for tree mortality from short- and long-term drought, and the potential for future fire.

The Impact

Forests identified as having low vulnerability could be targeted for preservation as carbon sequestration preserves. Research in high-vulnerability forests can identify management and environmental conditions that could delay or avoid ecosystem transformation. Communities in high–fire vulnerability areas may want to assess or improve their fire preparedness. These drought vulnerability metrics could be incorporated as probabilistic mortality rates in Earth system models, enabling more robust estimates of the feedbacks between the land and atmosphere under future conditions.

Summary
A research team from Oregon State University used the Community Land Model (CLM4.5) to determine forest vulnerability to mortality from drought and fire by the year 2049. They modified CLM to represent 13 major forest types in the western United States and ran simulations at a 4-km grid resolution, driven with climate projections from two general circulation models under one emissions scenario (RCP 8.5). The study developed metrics of vulnerability to short-term extreme and prolonged drought based on annual carbon allocation to stem growth and net primary productivity. They calculated fire vulnerability based on changes in simulated future area burned relative to historical area burned, for all forested grid cells. Projections indicate that water-limited forests in the Rocky Mountains, Southwest, and Great Basin regions will be the most vulnerable to future drought-related mortality, and vulnerability to future fire will be highest in the Sierra Nevada and portions of the Rocky Mountains. High–carbon density forests in the Pacific coast and western Cascades regions are projected to be the least vulnerable to either drought or fire. Importantly, differences in climate projections lead to only 1% of the domain with conflicting low and high vulnerability to fire and no area with conflicting drought vulnerability.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov

Principal Investigator
Beverly Law
Professor, Global Change Biology & Terrestrial Systems Science, Dept Forest Ecosystems & Society, Oregon State University, Corvallis, OR
bev.law@oregonstate.edu

Funding
This work was supported by the Office of Biological and Environmental Research (BER) within the U.S. Department of Energy (DOE) Office of Science (DE-SC0012194) and the U.S. Department of Agriculture National Institute of Food and Agriculture (NIFA) (2013-67003-20652, 2014-67003-22065), and DOE Oregon AmeriFlux Sites. High-performance computing resources on Cheyenne (https://doi.org/10.5065/D6RX99HX) were provided by the National Center for Atmospheric Research (NCAR) Computational and Information Systems Laboratory, sponsored by the National Science Foundation.

Publications
Buotte, P.C. et al. “Near-future forest vulnerability to drought and fire varies across the western US.” Global Change Biology Online 25(1), 290–303 (2018). [DOI:10.1111/gcb.14490]

Related Links
Terraweb.forestry.oregonstate.edu

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


November 20, 2018

Novel Sun-Induced Chlorophyll Fluorescence (SIF) Measurement System Advances New Science at Flux Sites

New SIF measurement system integrates seamlessly with existing eddy covariance data acquisition systems, allowing new science to be explored.

The Science
SIF provides critical information about ecosystem functioning and productivity. SIF observations complement eddy covariance (EC) measurements of net fluxes of carbon dioxide and water vapor. Measuring SIF is, however, challenging. There is a need for a system that integrates seamlessly with existing EC systems at flux sites. The Fluorescence Auto-Measurement Equipment (FAME) was designed to provide versatility, extensibility, autonomous operation, and ease of maintenance for acquiring large quantities of high-quality SIF data at flux sites. A prototype FAME has operated continuously at the Missouri Ozark AmeriFlux site since September 2016, providing high-quality measurements in a challenging environment. FAME observed saturation or even slight decrease of canopy SIF at high photosynthetically active radiation (PAR), similar to leaf photosynthesis. Diurnal hysteresis was also observed, with higher SIF in the morning than afternoon despite the same PAR levels. These patterns of SIF emission were likely caused by dynamic adjustments of energy use in photosynthesis in response to changing environmental conditions and by stress-induced movements of chloroplasts and leaves, which affected light interception.

The Impact
The technology and measurement protocol introduced in this study advances the coordinated observation of SIF and EC fluxes. The results obtained at an AmeriFlux site demonstrate that integrated EC/SIF observation enables new science and represents a step change in observational ecosystem research.

Summary
Long-term continuous SIF observations have the potential to greatly advance terrestrial ecosystem science. Realizing this potential, however, requires synergistic implementation of SIF measurements within EC flux networks. The FAME system and SIF measurement protocol were designed to fulfill this purpose. The innovative hardware and software of FAME support plug-and-play integration with existing EC data acquisition systems. A major novel feature of FAME is its synchronized sampling of spectral irradiance and environmental variables, allowing for more precise interpretation of the SIF signal. The continuous operation of FAME at the Missouri Ozark AmeriFlux site indicates that FAME has achieved its design objective. The light saturation response of SIF and asymmetrical diurnal patterns observed by FAME point to new directions in terrestrial ecosystem science that have not been previously explored.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science Program, SC-23.1
Daniel.Stover@science.doe.gov

Principal Investigator
Lianhong Gu
Oak Ridge National Laboratory
Oak Ridge, TN 37831
lianhong-gu@ornl.gov

Funding
Terrestrial Ecosystem Science program of the Office of the Biological and Environmental Research, within the the U.S. Department of Energy Office of Science.

Publication
Gu L, JD Wood, CYY Chang, Y Sun, JS Riggs. “Advancing terrestrial ecosystem science with a novel automated measurement system for sun-induced chlorophyll fluorescence for integration with Eddy covariance flux networks.” JGR-Biogeosciences 124(1), 127– 46 (2018). [DOI:10.1029/2018JG004742]

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


October 25, 2018

Forecasting the Decomposability of Organic Matter in Warming Tundra Soils

Infrared spectroscopy predicted the initial decomposition of active layer and permafrost organic matter in Arctic soils.

The Science
Calibration models derived from the mid infrared (MIR) spectra of arctic tundra soils reasonably estimated the amount of carbon dioxide released from decomposing soil organic matter during short-term laboratory incubations. Clays, phenolics, aliphatics, silicates, carboxylic acids, and amides were identified as the most influential soil components predicting the initial decomposition of tundra soil organic matter (SOM).

The Impact
The potential decomposability of soil organic matter is usually determined from soil incubations, which require a substantial investment of time and effort. Application of MIR calibration models to already collected and archived soils could enable widespread assessments of the potential decomposability of Arctic soil organic matter, which are needed to constrain and benchmark model simulations of the responses of these soils to changing environmental conditions.

Summary
Vast amounts of SOM are preserved in arctic soils due to the limiting effects of cold and wet environments on decomposer activity. With rapid high-latitude warming due to climate change, the potential decomposability of this soil organic matter needs to be assessed. A team led by Argonne National Laboratory investigated the capability of MIR spectroscopy to quickly predict the amount of organic matter mineralized to carbon dioxide during short-term incubations of arctic soils. Active layer and upper permafrost soils from four tundra sites on the North Slope of Alaska were incubated for 60 days. A partial least square regression (PLSR) model, constructed from the MIR spectra of all incubated soils, reasonably predicted the amount of carbon mineralized during the incubations. Comparing PLSR models for soil subgroups defined by soil carbon or nitrogen contents and tundra type revealed that the best predictions were obtained for soils with <10% organic carbon and <0.6% total nitrogen. Analysis of loadings and beta coefficients from the PLSR models indicated a small number of influential spectral bands, including those indicating clays, phenolics, aliphatics, silicates, carboxylic acids, and amides present in the soils. Study results suggest that MIR spectroscopy could be a useful tool for estimating the initial decomposability of tundra SOM, particularly for mineral soils and the mixed organic-mineral horizons of cryoturbated soils.

Contacts
BER Program Manager
Daniel Stover
Office of Biological and Environmental Research, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Principal Investigators
Julie D. Jastrow
Argonne National Laboratory
Lemont, IL 60439
jdjastrow@anl.gov (630-252-3226)

Corresponding Author
Roser Matamala
Argonne National Laboratory
Lemont, IL 60439
matamala@anl.gov (630-252-9270)

Funding
This study was supported by the Terrestrial Ecosystem Science program (TES) under the Climate and Environmental Science Division of the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy (DOE) Office of Science, under Contract No. DE-AC02-06CH11357 to Argonne National Laboratory.

Publications
Matamala, R., Jastrow, J.D., Calderón, F.J., Liang, C., Fan, Z., Michaelson, G.J. and Ping, C.L. “Predicting the decomposability of arctic tundra soil organic matter with mid infrared spectroscopy.” Soil Biology and Biochemistry 129, 1–12 (2019). [DOI:10.1016/j.soilbio.2018.10.014].

Related Links
Paper
SFA website

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


October 15, 2018

Arctic Greening Thaws Permafrost, Boosts Groundwater Flow

Models are used to understand how low-Arctic landscapes are changing in a warming climate.

The Science
Models of permafrost dynamics were used to show that snow drifts associated with tall shrub patches warm the underlying soil, resulting in holes called “through taliks” in the permafrost. Through taliks can activate deep flow pathways that significantly alter groundwater flow patterns in shrub-tundra landscapes.

The Impact
The resulting increases in groundwater discharge suggest that observed increases in tall shrub abundance throughout the Arctic may be a driver of observed increases in winter Arctic river discharge.

Summary
At hilly field sites in the southern Seward Peninsula, Alaska, patches of deep snow in tall shrubs are associated with higher winter ground temperatures. Reseachers from the Next-Generation Ecosystem Experiments (NGEE)–Arctic study show that through taliks—thawed zones extending through the entire permafrost layer—can form under these patches. The formation of through taliks creates new hydrologic pathways connecting the near surface to deeper regions, with significant hydrological and biogeochemical consequences. In particular, through taliks enable exchange and transport of nutrients and soil carbon from shallow upland hillslope sources to streams and lakes through groundwater discharge. To better understand the processes controlling and consequences of through taliks, researchers used NGEE–Arctic’s permafrost hydrology model, Arctic Terrestrial Simulator (ATS), to simulate through taliks associated with snow drifts. Scenarios were developed based on an intensively studied hillslope transect on the southern Seward Peninsula. In these scenarios, when through taliks formed, subpermafrost groundwater flow greatly increased. The simulations showed that through talik can form quickly (over a few decades) and then drive a rapid increase in subpermafrost groundwater.
 

Contacts
BER Program Manager
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Principal Investigators
Elchin Jafarov
Los Alamos National Laboratory
Los Alamos, NM 87545
elchin@lanl.gov

Ethan Coon
Oak Ridge National Laboratory
Oak Ridge, TN 37831
coonet@ornl.gov

Funding
This work is part of the Next-Generation Ecosystem Experiments (NGEE)–Arctic project, which is supported by the Office of Biological and Environmental Research within the U.S. Department of Energy (DOE) Office of Science.

Publications
Jafarov, E.E., E.T. Coon, D.R. Harp, C.J. Wilson, S.L. Painter, A.L. Atchley, & V.E. Romanovsky. “Modeling the role of preferential snow accumulation in through talik development and hillslope groundwater flow in a transitional permafrost landscape." Environmental Research Letters 13(10), 105006 (2018). [DOI:10.1088/1748-9326/aadd30].

Related Links
NGEE Arctic

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


October 01, 2018

Root Litter Decomposition Slows with Soil Depth

Novel use of 13C to quantify how deeper root inputs affect soil carbon storage.

The Science
Clever use of 13C isotopes revealed that plant tissues decompose more slowly the deeper they are in the soil profile. The restriction to decay was breaking down the coarse root particulates into finer particles that bacteria can transform.

The Impact
These results help bolster strategies for enhancing soil carbon sequestration and sustainable bioenergy production based on promoting deeper rooting by plants. Model results suggested that the lack of root exudates in deep soil limits microbial processes.

Summary
Although over half of the world’s soil organic carbon (SOC) is stored in subsoils (>20 cm deep), there are few studies examining in situ decomposition in deep soils. Researchers at Lawrence Berkeley National Laboratory added 13C-labeled fine roots to three depths (15 cm, 55 cm, and 95 cm) in the soil of a Ponderosa pine forest in California. They measured the amount of root-derived carbon remaining over 6, 12, and 30 months, in different soil fractions and in microbial phospholipid fatty acids (PLFAs). Root decomposition in the first 6 months was similar among all depths but diverged significantly by 30 months because decomposition at 95 cm nearly stopped. Mineral associations were not the cause of slower decomposition at depth because similar amounts of applied root carbon were recovered in the dense fraction at all depths. The largest difference among depths was in the amount of root carbon recovered in the coarse particulate fraction, which was much greater at 95 cm (50%) than at 15 cm (15%). There was more fungal and gram-negative bacteria biomass in the surface soil, and these groups may have facilitated rapid breakdown of particulates; they preferentially incorporated the added root carbon relative to native SOC. Simulations of these soils using the CORPSE model, which incorporates microbial priming effects and mineral stabilization of SOC, reproduced patterns of particulate and mineral-associated SOC over both time and depth and suggested that a lack of priming by root exudates at depth could account for the slower breakdown of particulate root material.

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Climate and Environmental Sciences Division (SC-23.1)
Terrestrial Ecosystem Science
daniel.stover@science.doe.gov

Principal Investigator
Margaret Torn  
Lawrence Berkeley National Laboratory
Berkeley, CA 94720
mstorn@lbl.gov

Funding
This material is based on work supported by the Terrestrial Ecosystem Science program of the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy, Office of Science, under Contract No. DE AC02-05CH11231.

Publications
Hicks Pries, C. E., B. N. Sulman, C. West, C. O'Neill, E. Poppleton, R. C. Porras, C. Castanha, B. Zhu, D. B. Wiedemeier, and M. S. Torn. “Root litter decomposition slows with soil depth.” Soil Biology and Biochemistry 125, 103–14 (2019). [DOI:10.1016/j.soilbio.2018.07.002]

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


September 28, 2018

New Free Online Modeling Tool Broadens Permafrost Research

User-friendly permafrost modeling toolbox aids students and researchers.

The Science
Researchers provided new online modeling tools to aid the study of permafrost, which is thawing rapidly due to climate change but many of the dynamics are unknown. Permafrost covers a quarter of the land in the Northern Hemisphere and stores vast amounts of organic carbon that could contribute to climate warming. A team developed online, easily accessible permafrost process models—the Permafrost Modeling Toolbox (PMT)—and educational materials and provided online labs for use by students, scientists, and stakeholders. Complex, resource-intensive model development remained a barrier to permafrost research, until now.

The Impact
Permafrost—ground that stays frozen for more than two consecutive years—stores twice as much carbon as currently exists in Earth’s atmosphere; most of it has been frozen for up to hundreds of thousands of years. There is an urgent need to better understand and predict the thawing dynamics, climate feedbacks, and profound influences on hydrology and infrastructure. In addition to greenhouse gas and toxic metal releases and altered groundwater flow, thawing permafrost significantly damages roads and infrastructure as it buckles beneath structures. Permafrost data are critically important for scientists, engineers, policymakers, indigenous communities, and the general public. Evaluating current and future conditions requires modeling, which often requires code development and extensive computational resources. The PMT provides open-source numerical models of permafrost dynamics and additional Earth surface processes, and they are designed for users ranging from students studying thermal processes to industrial or academic researchers assessing environmental systems and climate feedbacks.

Summary
The toolbox currently includes three permafrost models of increasing complexity: (1) an empirical model (Air Frost Number model) that predicts the likelihood of permafrost occurring at a given location, (2) an analytical-empirical model (Kudryavtsev model) that provides solutions to thermodynamic equations, and (3) a numerical heat flow model (Geophysical Institute Permafrost Lab model). Interfaces allow information to be passed between models.

The PMT includes sets of sample inputs representing a variety of conditions and locations to enable immediate use of different permafrost models. Easy-to-use user interfaces and open-source, online access make PMT accessible to a broad audience well beyond the permafrost research community and support linkages between permafrost dynamics and hydrological or landscape change.

Applications include calculating permafrost across Arctic sites, analyzing historic warming trends, mapping predicted permafrost, and comparing models with different complexities.

The PMT is part of a PermaModel collaboration between researchers at Los Alamos National Laboratory and the University of Colorado. The models are available through the Community Surface Dynamics Modeling System (CSDMS), an academic, industrial, and government Earth modeling partnership.

Contacts
BER Program Manager
Daniel Stover
Daniel.Stover@science.doe.gov, SC-23.1

Principal Investigators
Elchin Jafarov, elchin@lanl.gov
Irina Overeem, irina.overeem@colorado.edu

Funding
This work was supported by the National Science Foundation (award number 1503559) and by the Next-Generation Ecosystem Experiments (NGEE)–Arctic project, funded by the Office of Biological and Environmental Research within the U.S. Department of Energy Office of Science.

Publications
Overeem, I., E. Jafarov, K. Wang, K. Schaefer, S. Stewart, G. Clow, M. Piper, and Y. Elshorbany. “A modeling toolbox for permafrost landscapes.” Eos 99 (2018). [DOI:10.1029/2018EO105155]

Related Links

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


September 18, 2018

Representing Microtopography Effects in Hydrology Models

A novel subgrid model improves the representation of hydrologic processes.

The Science
Microtopography is known to be an important control on surface water retention, evaporation, infiltration, and runoff generation. Unfortunately, direct representation of microtopography effects in models of those processes is typically not feasible because of the high spatial and temporal resolution required. A subgrid model was developed to include microtopography effects in lower-resolution models, thus improving the representation of key hydrologic processes.

The Impact
The newly developed subgrid model is broadly applicable to disparate landscapes and significantly improves the representation of runoff generation and inundation compared with neglecting small-scale topography. The subgrid model enables process-resolving models of permafrost thermal hydrology to expand to catchment scales and decadal time frames. 

Summary
Fine-scale simulations using high-resolution digital elevation models highlight the importance of microtopography and its effects on integrated hydrology in polygonal tundra, hummocky bogs, and hillslopes with incised rills. A subgrid model that modifies the flow and accumulation terms in lower-resolution models replicates the microtopography-resolving simulations at orders-of-magnitude smaller computation cost. The subgrid model makes it possible to incorporate thaw-induced dynamic topography in simulations addressing the evolution of carbon-rich Arctic tundra in a warming climate.

Contacts
BER Program Managers
David Lesmes and Daniel Stover
SC-23.1
David.Lesmes@science.doe.gov (301-903-2977) and Daniel.Stover@science.doe.gov (301-903-0289)

Principal Investigator
Ahmad Jan
Climate Change Science Institute
Oak Ridge National Laboratory
Oak Ridge, TN 37831
jana@ornl.gov (865-576-8175)

Funding
This work was supported by the Interoperable Design of Extreme-scale Application Software (IDEAS) project and by the Next-Generation Ecosystem Experiments (NGEE)–Arctic) project, supported by the Office of Biological and Environmental Research (BER) within the U.S. Department of Energy Office of Science.

Publications
Jan, A., E.T. Coon, J.D. Graham, and S.L. Painter. “A subgrid approach for modeling microtopography effects on overland flow.” Water Resources Research 54(9), 6153–6167 (2018). [DOI:10.1029/2017WR021898]

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


September 18, 2018

Vegetation Demographics in Earth System Models: A Review of Progress and Priorities

An assessment of current approaches to including individual plant dynamics in ESMs and the need for new types of observations to benchmark these models.

The Science
A team from NCAR and NGEE-Tropics reviewed the state of the science for models that have attempted to include the dynamics of individual plants, including their growth and death, within coupled Earth system models (ESMs). They reviewed approaches to resolve environmental heterogeneity along key gradients of light, water, and nutrients; how differences in plant states determine the dynamics of competition for resources; and issues of scaling from groups to individuals.

The Impact
The researchers argue for the need for specific observations, including forest inventory data, rates of individual-level resource acquisition and use, and the observations that link individual-level growth and mortality rates to environmental conditions as key benchmarks to improve and test the next generation of ESMs.

Summary
Solving the problem of including processes such as growth and mortality of individual trees is needed to have a robust estimate of ecosystem responses and contributions to global change. ESMs have traditionally not included individual-level dynamics, instead using bulk ecosystem level properties. However, the limitations of this approach have become clearer and so multiple ESM groups are including plant demographic processes within them. They review multiple approaches across a wide range of ESMs, to discuss commonalities and differences between these approaches. In particular, they describe differing attempts to represent size- and trait-structured competition for within the canopy, water, and nutrients underground, and the role of disturbance and mortality processes in governing ecosystem heterogeneity. The research team describes a set of requirements for testing and benchmarking the models, with a focus on the need to test the competition among individuals for resources, and the need for observations that test scaling between individual-level vital rates and environmental conditions.

Contacts
BER Program Managers
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Dorothy Koch
Earth System Modeling, SC-23.1
Dorothy.koch@science.doe.gov (301-903-0105)

Renu Joseph
Regional and Global Climate Modeling, SC-23.1
renu.joseph@science.doe.gov (301-903-9237)

Principal Investigators
Rosie Fisher
National Center For Atmospheric Research
Boulder, CO 80307-3000
rfisher@ucar.edu (303.497.1706)

Charles Koven
Lawrence Berkeley National Laboratory
Berkeley, CA 94720
cdkoven@lbl.gov (510.486.6724)

Funding
CDK, BC, RK, JH, TP, JS, CX , and SPS were supported by the Next-Generation Ecosystem Experiments (NGEE)–Tropics project, which is supported by the Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science.

Publications
Fisher, R. A., Koven, C. D., Anderegg, W. R. L., Christoffersen, B. O., Dietze, M. C., Farrior, C., Holm, J. A., Hurtt, G., Knox, R. G., Lawrence, P. J., Lichststein, J. W., Longo, M., Matheny, A. M., Medvigy, D., Muller-Landau, H. C., Powell, TL., Serbin, S. P., Sato, H., Shuman, J., Smith, B., Trugman, A. T., Viskari, T., Verbeeck, H., Weng, E., Xu, C., Xu, X., Zhang, T., and Moorcroft, P. “Vegetation demographics in Earth System Models: a review of progress and priorities.” Global Change Biology 24(1), 35–54 (2018). [DOI:10.1111/gcb.13910]

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


September 11, 2018

Crown Damage and the Mortality of Tropical Trees

A study on crown damage, growth, and survival in a tropical forest in Borneo.

The Science
Tree death is the result of interactions between factors, including direct and indirect effects. Crown damage and previous growth mediated most of the effect of tree size, wood density, soil fertility, and habitat suitability on mortality.

The Impact
Crown damage and individual growth (growing more or less than typical for the species) are very important. Habitat is important because fertility and moisture influence individual growth, more than influencing mortality of trees inside or outside their preferred habitat.

Summary
What causes individual tree death in tropical forests remains a major gap in the understanding of the biology of tropical trees and leads to significant uncertainty in predicting global carbon cycle dynamics. Scientists from the Next-Generation Ecosystem Experiments (NGEE)–Tropics study and the Smithsonian Tropical Research Institute measured individual characteristics (diameter at breast height, wood density, growth rate, crown illumination, and crown form) and environmental conditions (soil fertility and habitat suitability) for 26,425 trees = 10 cm diameter at breast height belonging to 416 species in a 52-hectare (ha) plot in Lambir Hills National Park, Malaysia. They used structural equation models to investigate the relationships among the different factors and tree mortality. Crown form (a proxy for mechanical damage and other stresses) and prior growth were the two most important factors related to mortality. The effect of all variables on mortality (except habitat suitability) was substantially greater than expected by chance. Tree death is the result of interactions between factors, including direct and indirect effects. Crown form or damage and prior growth mediated most of the effects of tree size, wood density, fertility, and habitat suitability on mortality. Large-scale assessment of crown form or status may result in improved prediction of individual tree death at the landscape scale.

Contacts
BER Program Managers
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov

Dorothy Koch
SC-23.1
Dorothy.Koch@science.doe.gov

Principal Investigator
Stuart J. Davies
Smithsonian Institution
daviess@si.edu

Funding
The Lambir 52-ha plot was established as a collaboration between the Forest Department of Sarawak, Malaysia, Harvard University [National Science Foundation (NSF) awards DEB-9107247 and DEB-9629601), and Osaka City University (grants 06041094, 08NP0901, and 09NP0901). The research has been supported by the Asia program of the Arnold Arboretum (Harvard University), the Center for Tropical Forest Science–Forest Global Earth Observatory of the Smithsonian Tropical Research Institute, and NSF award DEB-1545761 to S.J.D.  G.A. and S.J.D. were supported as part of the Next-Generation Ecosystem Experiments (NGEE)–Tropics, funded by the Office of Biological and Environmental Research (BER) within the U.S. Department of Energy Office of Science.

Publications
Arellano, G., N.G. Medina, S. Tan, M. Mohamad, and S.J. Davies. “Crown damage and the mortality of tropical trees.” New Phytologist 221(1), 169–179 (2018). [DOI:10.1111/nph.15381]

Topic Areas:

Division: SC-33 BER


August 24, 2018

Seeing the Vegetation Canopy from Wind Measurements

Temporally dynamic canopy heights derived from momentum flux data across AmeriFlux sites.

The Science
This study evaluates an innovative and robust method for deriving the canopy height, a key descriptor of the Earth surface, from continuously measured wind statistics and momentum fluxes. Researchers from the University of California, Berkeley show its applicability for tracking the temporal dynamics of vegetation canopies, including plant growth, harvest, land-use change, and disturbance.

The Impact
Networks of eddy covariance tower sites (i.e., meteorological observation towers with high-frequency measurements of wind speed and surface fluxes) have collected ~108 hours of turbulent flux data worldwide. This study demonstrates the great potential of the flux-derived canopy heights for providing a new benchmark for regional and global Earth system models (ESMs) and satellite remote sensing of canopy structure.

Summary
Vegetation canopy height is a key descriptor of the Earth surface and is in use by many modeling and conservation applications. However, large-scale and time-varying data of canopy heights are often unavailable. This synthesis evaluates the calculation of canopy heights from the momentum flux data measured at eddy covariance flux tower sites. This study shows that the aerodynamic estimation of canopy heights robustly predicts the site-to-site and year-to-year differences in canopy heights across a wide variety of forests. The weekly canopy heights successfully capture the dynamics of vegetation canopies over growing seasons at cropland and grassland sites. These results demonstrate the potential of the flux-derived canopy heights for tracking the seasonal, interannual, and/or decadal dynamics of vegetation canopies including growth, harvest, land-use change, and disturbance. Given the amount of data collected and the diversity of vegetation covered by the global networks of eddy covariance flux tower sites, the flux-derived canopy height has great potential for providing a new benchmark for regional and global ESMs and satellite remote sensing of canopy structure.

Contacts
BER Program Manager
Daniel Stover
SC-23.1
Terrestrial Ecosystem Science
Daniel.Stover@science.doe.gov

Principal Investigator
Dennis Baldocchi
University of California, Berkeley
baldocchi@berkeley.edu

Housen Chu
Lawrence Berkeley National Laboratory
Berkeley, CA 94720
hchu@lbl.gov

Funding
This study is supported by FLUXNET and AmeriFlux Management Project, hosted by the Lawrence Berkeley National Laboratory, which is sponsored by the U.S. Department of Energy Office of Science (DE-SC0012456 and DE-AC02-05CH11231).

Publications
Chu, H. et al. “Temporal dynamics of aerodynamic canopy height derived from eddy covariance momentum flux data across North American Flux Networks.” Geophysical Research Letters 45(17), 9275–9287 (2018). [DOI:10.1029/2018GL079306]

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


August 20, 2018

Small Differences in Ombrotrophy Control Regional-Scale Variation in Methane Cycling among Sphagnum-Dominated Peatlands

Large variation in methane emissions among bogs suggests caution in scaling results and associated regional extrapolations.

The Science
A detailed biogeochemical and microbial study of three moss-dominated, low-pH peatlands in northern Minnesota, as well as a survey of methane production potentials in 19 peatlands in the Upper Peninsula of Michigan, showed a large difference in methane production and emissions in bog-like peatlands despite initial similarities. These experiments demonstrate that it is common to have high variation in methane cycling in seemingly similar peatlands within a single geographical region.

The Impact
Caution is urged in extrapolating results from a small number of bog and peatland sites to regional responses in methane dynamics in peatlands due to considerable variability in methane cycling.

Summary
There is limited understanding of the variability associated with methane (CH4) cycling among low-pH, Sphagnum moss–dominated peatlands within a geographical region. Here, a team of researchers from the University of Oregon and Chapman University report the results from two studies exploring the controls of CH4 cycling in peatlands from the Upper Midwest (USA). Potential CH4 production and resultant carbon dioxide (CO2):CH4 ratios varied by several orders of magnitude among 19 peatlands in the Upper Peninsula of Michigan. They also more intensively examined CH4 dynamics in three bog-like, acidic, Sphagnum-dominated peatlands in northern Minnesota. Net CH4 flux was lowest in the peatland with well-developed hummocks, and the isotopic composition of the :CH4 along with methanotroph gene expression indicated a strong role for CH4 oxidation in controlling net CH4 flux. These experiments demonstrate that it is common to have high variation in CH4 cycling in seemingly similar peatlands within a single geographical region. Caution should be used when extrapolating data from a single site to the landscape scale, even for outwardly very similar peatlands, and it is best to place manipulative experiments in multiple peatlands to encompass this variability. The macroscale development of peatlands, and concomitantly their microtopography as expressed in the proportion of hummocks, hollows, lawns, and pools, needs to be considered as central controls over CH4 emissions in methane modeling.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science
Daniel.Stover@science.doe.gov

Principal Investigators
Scott Bridgham
Institute of Ecology and Evolution
University of Oregon
Eugene, OR 97403-5289
bridgham@uoregon.edu

Jason Keller
Schmid College of Science and Technology
Chapman University
Orange, CA 92866 USA
jkeller@chapman.edu

Funding
This material is based on work supported by the Office of Biological and Environmental Research, within the U.S. Department of Energy (DOE) Office of Science, under award numbers DE-SC0008092, DE-SC0014416, DE-SC0007144, DESC0012288, and DE-SC0012088; the DOE Office of Science Graduate Fellowship Program (DE-AC05- 06OR23100); and the National Science Foundation under award number DEB-0816575.

Publications
Zalman, C. et al. "Small differences in ombrotrophy control regional-scale variation in methane cycling among Sphagnum-dominated peatlands." Biogeochemistry 139, 155–177 (2018). [DOI:10.1007/s10533-018-0460-z]

Zalman, C. et al. 2018. SPRUCE Small Differences in Ombrotrophy Control Regional-Scale Variation in Methane Cycling among Sphagnum-Dominated Peatlands: Supporting Data. Oak Ridge National Laboratory, Oak Ridge, Tenn., USA.

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


August 15, 2018

Using Isotopic Measurements to Diagnose Performance of Carbon Dynamics in Terrestrial Vegetation Models

Measurements of carbon-14 in plant tissues help to reduce uncertainties in predictions of an ecosystem carbon cycle simulation model.

The Science
This study compared three carbon cycle simulation models which differed in their representation of how trees allocate carbon to growth vs. storage. Carbon isotopes were used as tracers in the model, allowing quantification of the age and transit time of carbon through the system, and providing new insights into the temporal dynamics of carbon allocation by plants.

The Impact
The age and transit time of carbon cycling through ecosystems (which can be measured using 14C), serve as important diagnostics of model structure and could largely help to reduce uncertainties in model predictions.

Summary
Trees store carbohydrates, in the form of sugars and starch, as reserves to be used to power both future growth as well as to support day-to-day metabolic functions. These reserves are particularly important in the context of how trees cope with disturbance and stress—for example, as related to pest outbreaks, wind or ice damage, and extreme climate events. How quickly these reserves are used and replaced—i.e., their age—was assessed using carbon isotope analysis (14C). The isotope data were used to test and improve computer simulation models of carbon flow through forest ecosystems, with a focus on the mathematical representation of stored carbon reserves. The age of C in different pools, and the overall transit time of C through the system, were used as diagnostics to assess how different carbon allocation schemes influence rates of C cycling. The different model structures did not influence how much C was stored in the system at the conclusion of the model run, but they did result in large differences in age and transit time distributions. The inclusion of two storage compartments resulted in the prediction of a system mean age that was 7-10 years older than in the models with one or no storage compartments. These results suggest that ages and transit times, which can be indirectly measured using isotopic tracers, serve as important diagnostics of model structure and could largely help to reduce uncertainties in model structure and model predictions.

Contacts (BER PM)
Daniel Stover SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Professor Andrew Richardson
Northern Arizona University, Center for Ecosystem Science and Society and School of Informatics, Computing and Cyber Systems
Tel. 928 523 3049
Email Andrew.richardson@nau.edu

Funding
This research is based upon work supported by the US Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research.

Publications
Ceballos-Núñez, V., A.D. Richardson and C.A. Sierra. “Ages and transit times as important diagnostics of model performance for predicting carbon dynamics in terrestrial vegetation models.” Biogeosciences, 15(5),1607-1625 (2018). [DOI:10.5194/bg-15-1607-2018]
 

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


August 15, 2018

Warmer Temperatures Lengthen Growing Season, Increase Plants’ Vulnerability to Frost

Experimental warming treatments show how peatland forests may respond to future environmental change.

The Science
A warming experiment in a boreal peatland forest in Minnesota resulted in plants greening up earlier in spring, and staying green longer in autumn, indicating potential extension of the growing season by up to 3-6 weeks by the end of the current century. However, as plants greened up earlier, some also lost their winter hardiness: this exposed these individuals to damage when a spring frost hit in early April 2016.

The Impact
Recent warming trends have been shown to lengthen the growing season in temperate and Boreal ecosystems. Whether this trend will continue under future environmental conditions depends on whether other factors—such as day length (photoperiod)—become more limiting. This study resolves that debate by showing that with warming of up to +9°C above ambient, vegetation responses to increased temperature were linear, and not limited by day length.

Summary
The SPRUCE experiment is applying warming (0 to +9°C above ambient) and CO2 (ambient and elevated) treatments to intact communities of mature vegetation in a Boreal black-spruce sphagnum bog in the upper Midwest USA. Digital cameras mounted in each of the 10 experimental plots show that warming treatments linearly extend the period of vegetation activity in both spring and autumn. There was little evidence that daylength (photoperiod) limited these phenological shifts. The camera observations are consistent with ground observations of the timing of flowering and growth by a variety of bog plant species. In spring 2016, unusually warm weather in March was followed by extreme cold in early April. Vegetation in the warmest chambers (+6.75, +9.0 °C) suffered severe frost damage as the temperature dropped to -3 °C, indicating a premature loss of frost hardiness.   By comparison, vegetation in the cooler chambers (0, +2.25, +4.5 °C) was undamaged, despite experiencing dramatically colder temperatures (up to -15 °C). Thus, because phenological transitions - including loss of frost hardiness - appear to be temperature-driven, rather than cued by photoperiod, vegetation may be exposed to greater risk of frost damage in a warmer world. These in situ experimental results are of particular significance because Boreal forests have a circumpolar distribution and play a key role in the global carbon cycle.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Professor Andrew Richardson
Northern Arizona University, Center for Ecosystem Science and Society and School of Informatics, Computing and Cyber Systems
Tel. 928 523 3049
Email Andrew.richardson@nau.edu

Funding
This research is based upon work supported by the US Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for DOE under contract DE-AC05-00OR22725. Support for PhenoCam has come from the National Science Foundation (EF-1065029, EF-1702697).

Publications
Richardson, A.D., K. Hufkens, T. Milliman, D.M. Aubrecht, M.E. Furze, B. Seyednasrollah, M.B. Krassovski, J.M. Latimer, W.R. Nettles, R.R. Heiderman, J.M. Warren and P.J. Hanson. “Ecosystem warming extends vegetation activity but heightens vulnerability to cold temperatures.” Nature 560 368-371 (2018). [DOI: 10.1038/s41586-018-0399-1]

Related Links
PhenoCams

Topic Areas:

Division: SC-33 BER


August 14, 2018

Climate Sensitive Size-Dependent Survival in Tropical Trees

Important links indicated between evolutionary strategies, climate, and carbon cycling. 

The Science
Tropical forests have very high species diversity that poses a significant challenge to predictive understanding of tropical forest dynamics. Scientists from the Next-Generation Ecosystem Experiments (NGEE)–Tropics project found that tropical species could be classified into four "survival modes," which explain life-history variation in survival that shapes carbon cycling under different climate conditions as measured by annual temperature and cumulative water deficit.

The Impact
The consistent survival modes identified across different tropical forests allowed researchers to simulate the forest survival in a relatively small number of trackable functional types for hyper-diverse tropical forests within Earth System Models (ESMs). Frequently collected functional traits, such as wood density, leaf mass per area, and seed mass, were not generally predictive of the survival modes of species. Mean annual temperature and cumulative water deficit predicted the proportion of biomass of survival modes, indicating important links between evolutionary strategies, climate, and carbon cycling. As tree survival plays a key role in regulating vegetation dynamics, researchers expect that this analysis can provide insights to better simulate vegetation dynamics in ESMs.

Summary
Survival rates of large trees determine forest biomass dynamics. Survival rates of small trees have been linked to mechanisms that maintain biodiversity across tropical forests. How species survival rates change with size offers insight into the links between biodiversity and ecosystem function across tropical forests. Scientists from the NGEE-Tropics study tested patterns of size-dependent tree survival across the tropics using data from 1,781 species and over 2 million individuals to assess whether tropical forests can be characterized by size-dependent, life-history survival strategies. They found that species were classifiable into four "survival modes" that explain life-history variation that shapes carbon cycling and the relative abundance within forests. Frequently collected functional traits, such as wood density, leaf mass per area, and seed mass, were not generally predictive of the survival modes of species. Mean annual temperature and cumulative water deficit predicted the proportion of biomass of survival modes, indicating important links between evolutionary strategies, climate, and carbon cycling. Project results reveal globally identifiable size-dependent survival strategies that differ across diverse systems in a consistent way.

Contacts
BER Program Managers
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Dorothy Koch
SC-23.1
Dorothy.Koch@science.doe.gov (301-903-0105)

Principal Investigators
Chonggang Xu
Los Alamos National Laboratory
Los Alamos, NM 87545
cxu@lanl.gov

Nate McDowell
Pacific Northwest National Laboratory
Richland, WA 99352
nate.mcdowell@pnnl.gov

Funding
The first author, Daniel Johnson, was supported by Los Alamos National Laboratory (LANL; Director’s Post-Doctoral Fellowship). Contributions by Chonggang Xu, Jeff Chamber, Stuart David, and Nate McDowell were supported by the Next-Generation Ecosystem Experiments (NGEE)–Tropics) project, funded by the Office of Biological and Environmental Research within the U.S. Department of  Energy Office of Science. Sean McMahon was partially funded by the National Science Foundation (NSF-EF1137366).

Publications
Johnson, D. J. et al. “Climate sensitive size-dependent survival in tropical trees.” Nature Ecology & Evolution 2, 1436–1442 (2018). [DOI:10.1038/s41559-018-0626-z]

Related Links
BEHIND THE PAPER — Tropical tree survival: the large and the small of it

 

Topic Areas:

Division: SC-33 BER


August 14, 2018

Controls on Nitrogen Availability in the Arctic Tundra

Hydrological changes are key to determining nutrient cycling responses in complex polygonal tundra landscapes.

The Science
The unique aspects of the permafrost environment create new challenges for representing plant-nitrogen interactions in the Arctic tundra. Next-Generation Ecosystem Experiments (NGEE)–Arctic scientists from Oak Ridge National Laboratory (ORNL) measured how nitrogen availability to plants varies spatially and temporally in the Arctic tundra in relation to microhabitats and permafrost thaw.

The Impact
Arctic models should not assume that increasing thaw depth with warming of the Arctic will release additional nitrogen to the benefit of plants. Increased production of inorganic nitrogen that is not coupled to plant uptake could lead to nitrogen losses from the system and degradation of the ecosystem.

Summary
Nitrogen availability in the Arctic strongly influences plant productivity and distribution, and, in permafrost systems with patterned ground, ecosystem carbon and nutrient cycling can vary substantially over short distances. Improved understanding of fine-scale spatial and temporal variation in soil nitrogen availability is needed to better predict tundra responses to a warming climate. NGEE-Arctic scientists from ORNL quantified plant-available inorganic nitrogen at multiple soil depths in 12 micro-habitats associated with a gradient from low-center ice-wedge polygons to high-center polygons in coastal tundra at Utqiagvik (formerly Barrow), Alaska.  They measured vegetation composition, biomass, nitrogen content, and rooting depth distribution, as well as soil temperature, moisture, pH, and thaw depth to determine relationships between the spatial and temporal variability in nitrogen availability and environmental and vegetation drivers. Soil moisture variability across the complex polygonal terrain of the Barrow Environmental Observatory was the primary determinant of nitrogen availability. Drier habitats had a greater proportion of their nitrogen economy as nitrate rather than ammonium, but the plant species present could not exploit this resource. Nitrogen availability increased as the soil thawed during the summer, but the newly available nitrogen near the permafrost boundary late in the growing season was not available to roots. The strong relationship between soil moisture, inorganic nitrogen availability, and plant nitrogen content implies that understanding hydrological changes that may occur in a warming climate is key to determining nutrient cycling responses in complex polygonal tundra landscapes.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Principal Investigator
Richard J. Norby
Environmental Science Division and Climate Change Science Institute
Oak Ridge National Laboratory
Oak Ridge, TN 37831
norbyrj@ornl.gov

Funding
This work was funded by the Next-Generation Ecosystem Experiments (NGEE)–Arctic) project. The NGEE-Arctic project is supported by the Office of Biological and Environmental Research within the U.S. Department of Energy (DOE) Office of Science.

Publications
Norby, R.J., V.L. Sloan, C.M. Iversen, and J. Childs. “Controls on fine-scale spatial and temporal variability of plant-available inorganic nitrogen in a polygonal tundra landscape.” Ecosystems 22, 528–543 (2018, issue: 2019). [DOI:10.1007/s10021-018-0285-6]

Related Links
The datasets presented in this manuscript are available and can be accessed at http://dx.doi.org/10.5440/1129476http://dx.doi.org/10.5440/1121134,
http://dx.doi.org/10.5440/1120920, and https://dx.doi.org/10.5440/1375316  (Next-Generation Ecosystem Experiments Arctic Data Collection, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee, USA).

 

Topic Areas:

Division: SC-33 BER


August 14, 2018

Traits Drive Global Wood Decomposition Rates More than Climate

Inclusion of wood traits in global carbon cycle models could improve predictions of carbon fluxes from wood decomposition.

The Science
Current projections suggest an increase in dead wood biomass as a result of more frequent and intense climate extremes and disturbances (e.g., deforestation, storms, drought, heat waves, and fire) in the future, and thus wood decomposition plays a key role in regulating local and regional climates after disturbances. The decomposition rates depend on both wood characteristics (i.e., traits) and associated climates. This global meta-analysis study found that global variations in wood decomposition rates are mostly contributed by stoichiometric and geometric (e.g., surface area) wood traits (>50%), an amount much larger than that contributed by climates (~20%).

The Impact
nderstanding wood decomposition rates under global change is important for modeling the ecosystem feedbacks to climate. This study highlights the importance of wood traits for wood decomposition across global climate gradients, challenging the conventional view that climate is the dominant driver of decomposition rates at broad spatial scales. This perspective provides the basis for future development and parameterization of decomposition within most Earth system models.

Summary
Wood decomposition is a major component of the global carbon cycle. Decomposition rates vary across climate gradients, which are thought to reflect the effects of temperature and moisture on the metabolic kinetics of decomposers. However, decomposition rates also vary with wood traits, which may reflect the influence of stoichiometry on decomposer metabolism as well as geometry relating the surface areas that decomposers colonize with the volumes they consume. This study combined metabolic and geometric scaling theories to formalize hypotheses regarding the drivers of wood decomposition rates. It assessed these hypotheses using a global compilation of data on climate, wood traits, and wood decomposition rates. These results are consistent with predictions from both metabolic and geometric scaling theories. Approximately half the global variation in decomposition rates was explained by wood traits (nitrogen content and diameter), whereas only a fifth was explained by climate variables (air temperature, precipitation, and relative humidity). These results indicate that global variation in wood decomposition rates is best explained by stoichiometric and geometric wood traits. The findings suggest that inclusion of wood traits in global carbon cycle models can improve predictions of carbon fluxes from wood decomposition.

Contacts
BER Program Managers
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov

Dorothy Koch
SC-23.1
Dorothy.Koch@science.doe.gov

Principal Investigator
Chonggang Xu
Los Alamos National Laboratory
Los Alamos, NM 87545
cxu@lanl.gov

Funding
The manuscript's first author, Zhenhong Hu, was also supported by China Postdoctoral Science Foundation (2017M622709) and Foundation for High Level Talents in Higher Education of Guangdong, China (2014KZDXM018), which supported his visit to Los Alamos National Laboratory (LANL). Sean T. Michaletz and Daniel J. Johnson were supported by Director's Fellowships from LANL. Nate McDowell and Chonggang Xu were supported by the Next-Generation Ecosystem Experiments (NGEE)–Tropics project and Survival–Mortality experiment (SUMO) support from the U.S. Department of Energy Office of Science.

Publications
Hu Z., S.T. Michaletz, D.J. Johnson, N.G. McDowell, Z. Huang, X. Zhou, C. Hu. “Traits drive global wood decomposition rates more than climate.” Global Change Biology 24(11), 5259–5269 (2018). [DOI:10.1111/gcb.14357]

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


August 10, 2018

Modeling with Multiple Models Made Easy

New code allows scientists to generate and analyze multiple models that vary in how processes are represented.

The Science 
Researchers developed a new modeling software package that allows many alternative models to be posed, run, and analyzed as an ensemble, saving scientists time and providing a path to decrease uncertainty in modeling analyses.

The Impact
There are many ways to represent real-world processes in computer models. But it is common that only a single representation is used in any given model, leading to results that are model specific. This new code now allows the modeling community to move away from the single-representation method to using many alternative models in a single study for a richer analysis that more broadly encompasses the current state of knowledge about ecosystem processes.

Summary
Alternative ways that real-world processes can be represented in computer models is a huge source of uncertainty in model output. Yet, tools and modeling systems to examine these alternatives are not available. Researchers at Oak Ridge National Laboratory and a team of national and international collaborators have developed software that can combine alternative ways to represent many real-world processes into a complete set of all possible combinations of the alternatives. This will give a full range of possible model results and goes beyond the single-instance approach to running models. The software also includes novel tools for analysis of model sensitivity to alternative process models.

Contacts
BER Program Managers
Daniel Stover
Terrestrial Ecosystem Science
SC-23.1
Daniel.Stover@science.doe.gov

Dorothy Koch
Earth and Environmental System Modeling
SC-23.1
Dorothy.Koch@science.doe.gov

Principal Investigator
Anthony P. Walker
Oak Ridge National Laboratory
Oak Ridge, TN 37831
walkerap@ornl.gov

Funding
Oak Ridge National Laboratory Terrestrial Ecosystem Science Scientific Focus Area and Next-Generation Ecosystem Experiments (NGEE)–Tropics project by the Office of Biological and Environmental Research within the U.S. Department of Energy (DOE) Office of Science.

Publications
Walker, A. P. et al. “The multi-assumption architecture and testbed (MAAT v1.0): R code for generating ensembles with dynamic model structure and analysis of epistemic uncertainty from multiple sources.” Geoscientific Model Development 11(8), 3159–3185 (2018). [DOI:10.5194/gmd-11-3159-2018]

Related Links
Paper
GITHUB MAAT

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


August 01, 2018

Globally Rising Soil Heterotrophic Respiration over Recent Decades

A mutidecadal synthesis shows that soil microbes are respiring soil carbon at faster rates worldwide.

The Science
The results of this new study published in Nature show that soil microbes respire faster than photosynthesis rises in response to climate change, presumably leading to soil-carbon losses in many regions.

The Impact
There is perhaps no more pressing question in all of terrestrial biogeochemistry than the degree to which soils will respond to ongoing climate change—specifically, the degree to which they may lose some of their enormous carbon pools to the atmosphere, exerting a feedback effect on the climate. Whether such losses are occurring, or will in the future, has significant consequences for current understanding of how Earth’s ecosystems are changing.

Summary
Global soils store twice as much carbon as Earth’s atmosphere. This carbon may be destabilized by ongoing climate change, though to what degree remains uncertain. If soil-carbon losses do occur, the dominant pathway will be via heterotrophic soil respiration (RH), the soil-to-atmosphere flow of carbon dioxide produced by microbes.

This study collects thousands of observations over 25 years to show that RH is rising at a faster rate than either total soil respiration (the total soil-to-atmosphere carbon flux) or plant photosynthesis (as measured by satellites or by instruments on the ground, or as simulated in models). Collectively, these results provide strong evidence that global RH is responding to climate change, and they suggest that losses of soil carbon to the atmosphere may be occurring at large scales.

These results open new avenues of research—integrating remote sensing and observational data, for example, or developing new manipulative experiments of ecosystems. These results also offer new opportunities for testing Earth system models.

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Climate and Environmental Sciences Division (SC-23.1)
Terrestrial Ecosystem Science
daniel.stover@science.doe.gov

Principal Investigator
Ben Bond-Lamberty
Pacific Northwest National Laboratory
Richland, WA 99354
bondlamberty@pnnl.gov

Funding
This research was supported by the Terrestrial Ecosystem Science program of the Office Biological and Environmental Research, within the U.S. Department of Energy Office of Science. C.M.G. received additional support from the National Science Foundation Division of Environmental Biology.

Publications
Bond-Lamberty, B., et al. “Globally rising soil heterotrophic respiration over recent decades.” Nature 560, 80–83 (2018). [DOI:10.1038/s41586-018-0358-x]

Related Links
PNNL news release

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


July 27, 2018

Temperature Sensitivity of Deep Peat Microbial Enzymes

Stable temperatures in peat at depth appear to result in microbial community containing enzymes with lower sensitivity or responsiveness to temperature increases.

The Science
This study provides an improved understanding of the microbial mechanisms contributing to peat decomposition, reducing uncertainty around carbon cycling in these systems; however, results also suggest the potential for uncoupling of the nitrogen and carbon cycles as these environments evolve over time.

The Impact
There are large uncertainties about the fate of carbon stored in deep peat deposits under the changing environment. Understanding how microorganisms affect the decomposition of these deposits under varying conditions should help reduce this uncertainty.

Summary
Scientists from Oak Ridge National Laboratory hypothesized that the more stable recalcitrant subsurface environment would contain a smaller, less diverse microbial enzyme pool that is better adapted to a narrow temperature range. Potential enzyme activity decreased with peat depth as expected and corresponded with changes in peat composition and microbial biomass. Enzyme activation energy decreased with depth as predicted; however, leucine amino peptidase activation energy was much lower than other enzymes, suggesting a limited ability for these nitrogen-acquiring enzymes to increase activity with increased temperatures. Stable temperatures at depth in the peat appear to result in a microbial community containing enzymes that have lower sensitivity or responsiveness to temperature increases.

Contacts
BER Program Manager
Daniel Stover 
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov

Principal Investigator
Christopher W. Schadt
Senior Staff Scientist
Oak Ridge National Laboratory
Oak Ridge, TN 37831
schadtcw@ornl.gov

Funding
Supported by the Terrestrial Ecosystem Science (TES) program as part of the Oak Ridge National Laboratory (ORNL) SPRUCE project under the TES Scientific Focus Area (SFA) through the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy Office of Science, and by a university-led project of The Georgia Institute of Technology (grant number # DE-SC0012088).

Publications
Steinweg, J.M., J.E. Kostka, P.J. Hanson, and C.W. Schadt. “Temperature sensitivity of extracellular enzymes differs with peat depth but not with season in an ombrotrophic bog.” Soil Biology and Biochemistry 125, 244–250 (2018). [DOI:10.1016/j.soilbio.2018.07.001]

Related Links
http://mnspruce.ornl.gov   

Topic Areas:

Division: SC-33 BER


July 16, 2018

Getting To Know the Microbes that Drive Climate Change

The genetics of viruses living along a permafrost thaw gradient may help scientists better predict the pace of climate change.

The Science
Ocean viruses impact carbon and nutrient cycling and the climate. What impact to do viruses that inhabit the soil have? To answer key questions about soil viruses, a team recovered the genomic sequences from ~2,000 soil viral populations. They also retrieved multiple lines of evidence for viral impacts on carbon cycling in climate-impacted thawing permafrost ecosystems.

The Impact
Soil viruses have been studied less than their ocean counterparts because of the difficulty in examining them in a complex environment. Some people suggested these viruses were the “least important” factor for structuring soil microbial communities. On the contrary, this work suggests that viruses impact terrestrial ecosystems by directly and indirectly modifying soil microbial food webs. These webs degrade complex carbon to the greenhouse gases carbon dioxide and methane.

Summary
Over the last two decades, scientists have learned a great deal about the impacts of ocean viruses on microbial mortality, carbon and nutrient cycling, and climate, yet they know next to nothing about soil viruses. A team led by an ecologist from The Ohio State University sampled and assessed soils for the microbial and viral populations present. They focused on soils from a portion of Sweden in the Arctic Circle where the permafrost is rapidly changing. The approximately 2,000 soil viruses they recovered were so novel that they have doubled the total number of known microbe-infecting viral groups worldwide. More than half of these viruses were active, which was unexpected given soil’s propensity for preservation, and approximately a third were linked to microbial hosts that included key carbon cycling microbes predominant in thawing permafrost soils. This implies viral controls on soil carbon cycling and provides first looks, in any ecosystem, at lineage-specific virus:host ratios and how viral pressures change along a thaw gradient. These observations suggest that viral infection dynamics and impacts on host-driven biogeochemistry will change as permafrost thaws. In addition, the recovery of virus-encoded glycoside hydrolase genes suggests that viruses may directly enable degradation of plant-derived polymers to monomeric and small oligomeric sugars during infection to supply bioavailable carbon sources to greenhouse gas-emitting microbial food webs. These findings suggest that soil viruses, just like their ocean counterparts, impact ecosystem function and in these climate-critical, terrestrial habitats will alter the trajectory of soil carbon cycling under a thaw regime.

Contact

Program Manager
Dawn Adin
DOE Office of Biological and Environmental Research, Biological Systems Science Division
Dawn.Adin@science.doe.gov

Matthew B. Sullivan 
The Ohio State University
sullivan.948@osu.edu

Virginia Rich 
The Ohio State University
rich.270@osu.edu

Funding
This research was supported by the Department of Energy, Office of Science, Office of Biological and Environmental Research under the Genomic Science program, with partial support from the Gordon and Betty Moore Foundation and National Science Foundation awards (M.B.S.). Further, A.E.N. and P.B.P. were supported by the European Research Council.

Publications
J.B. Emerson, S. Roux, J.R. Brum, et al., “Host-linked soil viral ecology along a permafrost thaw gradient.” Nature Microbiology 3, 870 (2018). [DOI: 10.1038/s41564-018-0190-y]

Related Links
The Ohio State University press release: Getting to know the microbes that drive climate change
Broader IsoGenie project page: https://isogenie.osu.edu/  
Sullivan Lab Viral Ecology webpage: http://u.osu.edu/viruslab/
Emerson Lab Viral Ecology webpage: https://emersonlab.faculty.ucdavis.edu/

Topic Areas:

Division: SC-33.2 Biological Systems Science Division, BER


June 02, 2018

Simulating the Spatial Variation of Carbon Processes at a Critical Zone Observatory

Development and testing of a spatially distributed land surface hydrologic biogeochemistry model with nitrogen transport.

The Science
A distributed land surface hydrologic biogeochemistry model with nitrogen transport processes is developed and tested at the Shale Hills watershed. The model is able to represent the spatial variations in terrestrial carbon processes and suggests that tree growth at the Shale Hills watershed is nitrogen limited.

The Impact
The coupled Flux-PIHM-BGC model provides an important tool to study spatial variations in terrestrial carbon and nitrogen processes and their interactions with environmental factors, and to predict the spatial structure of the responses of ecosystems to climate change.

Summary
A spatially distributed land surface hydrologic biogeochemical model with nitrogen transport, Flux-PIHM-BGC, has been developed by scientists at Pennsylvania State University by coupling a  one-dimensional (1D) mechanistic biogeochemical model, Biome-BGC (BBGC), with a spatially distributed land surface hydrologic model, Flux-PIHM, and adding an advection dominated nitrogen transport module. In the coupled Flux-PIHM-BGC model, each Flux-PIHM model grid couples a 1D BBGC model, while nitrogen is transported among model grids via surface and subsurface water flow. The coupled Flux-PIHM-BGC model has been implemented at the Susquehanna Shale Hills Critical Zone Observatory. The model-predicted aboveground vegetation carbon and soil carbon distributions generally agree with the macro patterns observed within the watershed, although the model underestimates the spatial variability. Model results suggest that the spatial pattern of aboveground carbon is controlled by the distribution of soil mineral nitrogen. A Flux-PIHM-BGC simulation without the nitrogen transport module is also executed. The model without nitrogen transport fails in predicting the spatial patterns of vegetation carbon, indicating the importance of having a nitrogen transport module in spatially distributed ecohydrologic modeling.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem System, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Principal Investigator
David Eissenstat
The Pennsylvania State University
University Park, Pennsylvania 16802
dme9@psu.edu (814)863-3371

Funding
This work is supported by the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy Office of Science, under Award Number DE-SC0012003, and facilitated by the National Science Foundation Critical Zone Observatory program grants to CJD (EAR 07- 25019) and SLB (EAR 12-39285 and EAR 13-31726).

Publications
Shi, Y., Eissenstat, D. M., He, Y., & Davis, D. J. “Using a spatially-distributed hydrologic biogeochemistry model with a nitrogen transport module to study the spatial variation of carbon processes in a Critical Zone Observatory.” Ecological Modelling 380, 8–21 (2018). [DOI:10.1016/j.ecolmodel.2018.04.007].

Related Links
Link to the Flux-PIHM-BGC repository: https://github.com/PSUmodeling/MM-PIHM

 

Topic Areas:

Division: SC-33 BER


May 31, 2018

Local Heterogeneity of Carbon Accumulation Throughout the Peat Profile of an Ombrotrophic Northern Minnesota Bog

Past carbon accumulation in peat of the SPRUCE bog helps understand response to experimental treatments.

The Science 
Scientists from Oak Ridge National Laboratory (ORNL) and Lawrence Livermore National Laboratory (LLNL) measured carbon storage and age of 18 peat depth profiles at the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experimental site, constructed peat age-depth models, and quantified rates of carbon accumulation over the history of the bog to assess potential sources for variation in accumulation of carbon over time and space. Calibrated peat ages and age-depth profiles are available for use by SPRUCE collaborators and the broader community.

The Impact
This study found that the bog has been accumulating carbon in peat for over 11,000 years. Carbon accumulation rates changed over time, with a period of low net carbon accumulation likely a result of warmer and drier environmental conditions between 100 and 3300 years before present. These results suggest that experimental warming treatments, as well as a future warmer climate, may reduce net carbon accumulation in peat in this and other southern boreal peatlands.

Summary
ORNL and LLNL scientists evaluated the spatial heterogeneity of historical carbon accumulation rates in a forested, ombrotrophic bog in Minnesota to aid understanding of responses to an ongoing decade-long warming manipulation (SPRUCE). Eighteen peat cores indicated that the bog has been accumulating carbon for over 11,000 years, to yield an average of 176 kg C per m2 to 225 cm of peat depth. The long-term apparent rate of carbon accumulation over the entire peat profile averaged 22 kg C m2 yr–1. Net carbon accumulation rates averaged 30 ± 2 g C m2 yr–1 prior to 3300 cal BP, when net carbon accumulation rates dropped to 15 ± 8 g C m2 yr–1. Net carbon accumulation rates increased again during the last century to 74 ± 57 g C m2 yr–1. During the period of low accumulation, regional droughts may have lowered the water table, allowing for enhanced aerobic decomposition and making the bog more susceptible to fire. These results suggest that experimental warming treatments, as well as a future warmer climate, may reduce net carbon accumulation in peat in this and other southern boreal peatlands.

Contacts 
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Principal Investigators
Karis McFarlane
Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory
Livermore, CA 94550
kjmcfarlane@llnl.gov (925-423-6285)

Paul Hanson
Oak Ridge National Laboratory
Oak Ridge, TN 37381
hansonpj@ornl.gov (865-574-5361)

Funding
This work was supported by the Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science, under project ERKP788 and SWC1447; and Lawrence Livermore National Laboratory, Laboratory Research and Development project 14-ERD-038.

Publications
McFarlane KJ, Hanson PJ, Iversen CM, Phillips JR, Brice DJ. “Local spatial heterogeneity of Holocene carbon accumulation throughout the peat profile of an ombrotrophic Northern Minnesota bog.” Radiocarbon 60(3), 941–962 (2018). [DOI:10.1017/RDC.2018.37]

Topic Areas:

Division: SC-33 BER


May 31, 2018

Surviving the Heat: Resilience to Extreme Temperatures Varies by Species

Researchers find differing photosynthetic damage in four co-occurring temperate tree species.

The Science
Summer heat waves cause damage to leaves and stems in temperate forest ecosystems, affecting the short- and long-term survival of plants. Scientists at Oak Ridge National Laboratory studied and detailed the response and recovery of several southeastern tree species after short-term heat waves. By monitoring specific trait behavior, the research team characterized each tree’s reaction to being kicked into survival mode for brief periods of time and found that different tree species display varying degrees of photosynthetic damage, primarily to chlorophyll systems.

The Impact
The research team found that heat-induced damage to a key photosynthetic mechanism [photosystem II ((PSII)] could serve as a good mechanistic trait and indicator to improve projections of how different species respond to extreme weather events.

As heat waves continue to occur, and even strengthen in the future, improved understanding of the sensitivity of different species to extreme temperatures will allow for better predictions of heat wave effects on species distribution and ecosystem function under changing environmental conditions.

Summary
Scientists gained new insights about the mechanisms and thresholds for damage among tree species enduring short-term heat waves. This new knowledge could fill a gap in current simulations of forest growth response to shifting environmental conditions. Current models do not address the variability in response between co-occurring tree species to temperature extremes. To address this, the team exposed sets of saplings from southern red oak, Shumard oak, tulip-poplar, and eastern white pine to dramatic temperature swings that peaked at 51ºC in a climate-controlled test chamber. Sensors attached to each tree and located throughout the chamber tracked indicators of heat and drought stress such as fluxes in carbon uptake, shifts in water demand, and changes in chlorophyll fluorescence and PSII activity. A significant increase in both transient and chronic damage to PSII within the leaf chloroplasts was evident in the most heat sensitive species, pine and tulip poplar. The oaks, especially southern red oak, showed greater tolerance to heat and rapid overnight recovery. The findings indicate that differential heat-induced damage to PSII within the leaf chloroplasts may be a mechanistic trait that can be used to project how different species respond to extreme weather events, improving predictions of forest response to extreme temperatures.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov

Principal Investigators
Anirban Guha
Environmental Sciences Division and Climate Change Science Institute
Oak Ridge National Laboratory
Oak Ridge, TN 37831
guha2009anirban@gmail.com

Jeffrey M. Warren
Environmental Sciences Division and Climate Change Science Institute
Oak Ridge National Laboratory
Oak Ridge, TN 37831
warrenjm@ornl.gov

Funding
Support was through the Terrestrial Ecosystem Science program of the Office of Biological and Environmental Research, within the U.S. Department of Energy (DOE) Office of Science, and by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for DOE under contract DEAC05-00OR22725.

Publications
Guha A., J. Han, C. Cummings, D.A. McLennan, and J.M. Warren. “Differential ecophysiological responses and resilience to heat wave events in four co-occurring temperate tree species.” Environmental Research Letters 13(6) 065008 (2018). [DOI:10.1088/1748-9326/aabcd8]

Related Link
Oak Ridge National Laboratory Story Tip: https://www.ornl.gov/news/plants-surviving-heat

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


May 24, 2018

21st Century Tundra Shrubification Could Enhance Net Carbon Uptake of North America Arctic Tundra Under an RCP8.5 Climate Trajectory

Tundra shrubification will offset respiratory carbon losses under RCP8.5.

The Science
Scientists at Lawrence Berkeley National Laboratory (LBNL) and the Next-Generation Ecosystem Experiments (NGEE)–Arctic project applied an ecosystem model, ecosys, to examine the effects of North America Arctic tundra plant dynamics on ecosystem carbon balances from 1980 to 2100 under Representative Concentration Pathway (RCP) 8.5 scenario. Between 1982 and 2100 and averaged across the region, predicted increases in relative dominance of woody versus nonwoody plants increased ecosystem annual net primary productivity that offset concurrent increases in annual heterotrophic respiration, resulting in an increasing net carbon sink over the 21st century. However, modeled soil temperatures were predicted to increase more slowly than air temperatures, implying that higher gains versus losses of carbon may be a transient response and not sustainable under further soil warming beyond 2100.

The Impact
Although several tundra warming experiments provide valuable warming scenarios, the responses of these experiments were largely dependent on site conditions. Further, these experiments cannot fully represent the warming effects associated with relatively slower changes in species composition and abundance. Thus, this modeling analysis allows researchers to extend beyond results from short-term warming experiments, which cannot characterize effects associated with decadal-scale changes in plant communities.

Summary
NGEE-Arctic scientists applied a mechanistic trait-based model (ecosys) that represents key biological, physical, and chemical processes controlling long-term carbon cycle dynamics. In particular, they examined the roles of plant internal resource allocation and remobilization and microbial soil carbon, nitrogen, and phosphorus transformations, along with soil thermal and hydrological dynamics, over the 21st century. The effects of projected increases in tundra shrub growth on net ecosystem productivity were shown to enhance the ecosystem carbon sink due to increasing woody versus nonwoody carbon stocks. The modeled gains in nonwoody plant net primary productivity offset ecosystem respiration resulting in the tundra remaining a carbon sink through 2100.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov

Principal Investigator
William J. Riley
Lawrence Berkeley National Laboratory
Berkeley, CA 94720
wjriley@lbl.gov

Funding
This research was supported by the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy Office of Science, under Contract No. DE-AC02-05CH11231 as part of the Next-Generation Ecosystem Experiments (NGEE)–Arctic project.

Publications
Mekonnen, A.M., W.J. Riley, and R.F. Grant. "21st century tundra shrubification could enhance net carbon uptake of North America Arctic tundra under an RCP8.5 climate trajectory." Environmental Research Letters 13(5), 054029 (2018). [DOI:10.1088/1748-9326/aabf28]

Topic Areas:

Division: SC-33 BER


May 24, 2018

Accelerated Nutrient Cycling and Increased Light Competition Will Lead to 21st Century Shrub Expansion in North American Arctic Tundra

Climate change under RCP8.5 in the 21st century will enhance tundra shrubification.

The Science
Next-Generation Ecosystem Experiments (NGEE)–Arctic scientists from Lawrence Berkeley National Laboratory (LBNL) used an ecosystem model, ecosys, to mechanistically represent the processes controlling recent and 21st century changes in plant functional type (PFTs) across North American Arctic tundra. The productivity of deciduous and evergreen shrubs was modeled to increase across much of the tundra, particularly in Alaska and tundra-boreal ecotones. The increased canopy cover of shrubs reduced incoming shortwave radiation for low-lying plants, causing declines in net ecosystem productivity of graminoids and nonvascular plants.

The Impact
This study mechanistically modeled and explained the driving factors that control shrubification and its future trajectory under Representative Concentration Pathway (RCP) 8.5 scenario. LBNL scientists highlighted the importance of capturing the basic processes of how Arctic PFTs compete for irradiance, water, and nutrients, which are key mechanisms of how plant functional types may change under future climates. Their modeling approach also highlights the need to understand and model differences in functional traits of Arctic PFTs. Short-term experiments may not capture decadal-scale changes in carbon cycling driven by plant compositional changes.

Summary
Many large-scale land surface models do not represent biological and physical processes important to predicting how future changes in climate and environment will drive PFT changes, and thus they cannot mechanistically explain the dynamic factors that control these changes. The modeling approach applied here is driven by PFT-specific functional traits important for predicting high-latitude vegetation competition under a changing climate (e.g., carbon dioxide fixation kinetics, leaf optical properties, phenology, morphology, and root traits). Modeled differences in PFT functional traits determine the strategy of resource acquisition and allocation that drive growth, resource remobilization, and litterfall, and therefore each PFT’s dynamic competitive capacity under changing growing conditions. Deciduous and evergreen shrub productivity (i.e., shrubification) was modeled to increase over the 21st century across much of the tundra, particularly in Alaska and tundra-boreal ecotones.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov

Principal Investigator
William J. Riley
Lawrence Berkeley National Laboratory
Berkeley, CA 94720
wjriley@lbl.gov

Funding
This research was supported by the Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science, of the under Contract No. DE-AC02-05CH11231 as part of the Next-Generation Ecosystem Experiments (NGEE)–Arctic project.

Publications
Mekonnen, Z.A., W.J. Riley, and R.F. Grant. “Accelerated nutrient cycling and increased light competition will lead to 21st century shrub expansion in North American Arctic tundra.” Journal of Geophysical Research: Biogeosciences 123(5), 1683–1701 (2018). [DOI:10.1029/2017JG004319]

Topic Areas:

Division: SC-33 BER


May 22, 2018

Soil Microbial Controls on CO2 Fluxes in a Tropical Dry Forest

Identifying key mechanisms underlying carbon cycling dynamics in a vulnerable, highly seasonal tropical dry forest ecosystem.

The Science
In dry or semiarid ecosystems, most soil respiration [carbon dioxide (CO2) production by microorganisms] can occur in large "pulses" immediately following rainfall events. An in situ rainfall manipulation experiment was combined with a simulation modeling approach to identify the dominant belowground controls on these important CO2 fluxes.

The Impact
Dissolved organic carbon availability to microbes was identified as a key controller of soil CO2 pulses following rainfall events. This relationship can be captured in simple ecosystem models, allowing a better prediction of how the ecosystem carbon balance will respond to ongoing changes in precipitation regime.

Summary
An in situ precipitation manipulation experiment was conducted in a tropical dry forest in Guanacaste, Costa Rica, to better understand the processes underlying rainfall-induced pulses of soil respiration. (Re)-wetting dry soil produced an immediate, substantial pulse of CO2, accompanied by rapid immobilization of nitrogen into the microbial biomass. The size of the CO2 pulse following simulated rainfall events was linked to dissolved organic carbon (DOC) availability to microbes. The relationships among soil moisture, DOC, and CO2 fluxes were then integrated into simple biogeochemical models, which could accurately predict observed patterns of CO2 flux in response to rainfall. Together, these data demonstrate that explicitly representing microbial processes in such models can improve predictions of carbon cycling under changing rainfall regimes.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Principal Investigator
Jennifer Powers
University of Minnesota
St. Paul, MN 55108
powers@umn.edu

Funding
The Terrestrial Ecosystem Science (TES) program of the Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science, (award number DESC0014363) and the National Science Foundation (CAREER grant DEB 1053237 to JSP).

Publications
Waring, B.G., and Powers, J.S. "Unraveling the mechanisms underlying pulse dynamics of soil respiration in tropical dry forests." Environmental Research Letters 11(10), 105005 (2016). [DOI:10.1088/1748-9326/11/10/105005]

Topic Areas:

Division: SC-33 BER


May 07, 2018

Depth-Resolved Physicochemical Characteristics of Active Layer and Permafrost Soils in an Arctic Polygonal Tundra Region

Permafrost physicochemical property trends and variabilities.

The Science
Next-Generation Ecosystem Experiments (NGEE)–Arctic scientists from Oak Ridge National Laboratory (ORNL) explore the trends and variabilities of the permafrost physicochemical properties.

The Impact
These results are critical for identifying approaches to upscale point-based measurements and for improving model parameterization to predict permafrost carbon behavior and feedback under future climate.

Summary
NGEE-Arctic scientists from ORNL observed (1) consistent relationships between soil property and depth and between major parameters; (2) large contrasts of key soil parameters between active layer and permafrost, indicative of potentially different response of the permafrost carbon to warming when compared to the active layer; and (3) a correlation between soil hydraulic conductivity and topographic features that impacts soil hydrologic processes. This analysis suggests that the permafrost has a marine-derived chemical signature that differs from the active layer and shapes the physicochemical fingerprints of the different geomorphic features. Specifically, they revealed the unique signatures of the high-center polygons, indicative of possible microbial activity at depth (>1 m). Their study suggested consistent key soil parameter–depth correlations while demonstrating complex lateral and vertical variabilities.

Contacts
BER Program Manager
Dan Stover
Terrestrial Ecosystem Science, SC-23.1
daniel.stover@science.doe.gov

Principal Investigator
Stan Wullschleger
Oak Ridge National Laboratory
Oak Ridge, TN 37831
wullschlegsd@ornl.gov

Funding
The Next-Generation Ecosystem Experiments (NGEE)–Arctic project is supported by the Office of Biological and Environmental Research, within the U.S. Department of Energy (DOE) Office of Science. This NGEE-Arctic research is supported through contract number DE-AC0205CH11231 to Lawrence Berkeley National Laboratory.

Publications
Wu, Y., C. Ulrich, T. Kneafsey, R. Lopez, C. Chou, J. Geller, et al. “Depth-resolved physicochemical characteristics of active layer and permafrost soils in an Arctic polygonal tundra region.” Journal of Geophysical Research: Biogeosciences 123(4), 1366–1386 (2018). [DOI:10.1002/2018JG004413]

Related Links
The datasets presented in this manuscript are available and can be accessed at and cited as Yuxin Wu, Craig Ulrich, and Timothy J. Kneafsey. 2018. Physical, Chemical, and Hydrologic Characteristics of Active Layer and Permafrost Soils of Arctic Polygonal Tundra, Barrow, Alaska, 2013-2016. Next-Generation Ecosystem Experiments Arctic Data Collection, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee, USA. Dataset accessed on 2018 [DOI:10.5440/1358456].

PAPER: https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2018JG004413

Topic Areas:

Division: SC-33 BER


May 04, 2018

Contribution of Environmental Forcings to U.S. Runoff Changes for the Period 1950-2010

Understanding and attributing long-term trends of US runoff changes.

The Science 
This study examines the annual and seasonal trends of U.S. runoff for the 1950-2010 period. Models and measurements are used to study how and why run-off has changed in different regions and seasons of the U.S.

The Impact
Statistical methods, modeling, and observations were used to show significant changing trends and quantification of the environmental driving mechanisms for the US runoff during the 1950-2010 period.

Summary
Runoff in the United States is changing, and this study finds that the measured change is dependent on the geographic region and varies seasonally. Specifically, observed annual total runoff had an insignificant increasing trend in the U.S. between 1950 and 2010, but this insignificance is due to regional heterogeneity with both significant and insignificant increases in the eastern, northern, and southern U.S., and a greater significant decrease in the western U.S. Trends for seasonal mean runoff also differs across regions. By region, the season with the largest observed trend is autumn for the east (positive), spring for the north (positive), winter for the south (positive), winter for the west (negative), and autumn for the U.S. as a whole (positive). Based on the detection and attribution analysis using gridded WaterWatch runoff observations along with semi-factorial land surface model simulations from the Multi-scale Synthesis and Terrestrial Model Intercomparison Project (MsTMIP), we find that while the roles of CO2 concentration, nitrogen deposition, and land use and land cover appear inconsistent regionally and seasonally, the effect of climatic variations is detected for all regions and seasons, and the change in runoff can be attributed to climate change in summer and autumn in the south and in autumn in the west. We also find that the climate-only and historical transient simulations consistently underestimated the runoff trends, possibly due to precipitation bias in the MsTMIP driver or within the models themselves.

Contacts (BER PM)
Daniel Stover, Renu Joseph, and Dorothy Koch
Daniel.Stover@science.doe.gov, renu.joseph@science.doe.gov and dorothy.koch@science.doe.gov

PI Contact
Jiafu Mao
Environmental Sciences Division and Climate Change Science Institute, Oak Ridge National Laboratory, maoj@ornl.gov

Funding
W. Forbes, J. Mao, X. Shi, D.M. Ricciuto, P.E. Thornton, and F.M. Hoffman are supported by DOE Office of Science, Biological and Environmental Research, including support from the following programs:
Terrestrial Ecosystem Science Program, Regional and Global Climate Modeling Program (RUBISCO SFA), and the Earth System Modeling Program (the Energy Exascale Earth System Model (E3SM) project).

Publications
Forbes, W., J.  Mao, M. Jin*, S.-C. Kao, W. Fu, X. Shi, D.M. Riccuito, P. E. Thornton, A. Ribes, Y. Wang, S. Piao, T. Zhao, C.R. Schwalm, F.M. Hoffman, J.B. Fisher, A. Ito, B. Poulter, Y. Fang, H. Tian, A. Jain, and D. Hayes. “Contribution of environmental forcings to US runoff changes for the period 1950-2010.” Env. Res. Lett. 13 054023 (2018). [DOI: 10.1088/1748-9326/aabb41]

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


May 03, 2018

Vulnerability of Amazon Forests to Storm-Driven Tree Mortality

Wind-related tree mortality is important for reliable prediction of tropical forests and their effects on the Earth system.

The Science
Researchers from the Next-Generation Ecosystem Experiments (NGEE)–Tropics team found that wind-related tree mortality driven by storms (windthrows) are common in the Amazon region, extending from northwest (Peru, Colombia, Venezuela, and west Brazil) to central Brazil, with the highest occurrence of windthrows in the northwestern Amazon (NWA). More frequent winds, produced by more frequent severe convective systems, in combination with well-known processes that limit the anchoring of trees in the soil, help to explain the higher vulnerability of NWA forests to winds.

The Impact
The higher frequency of windthrows in NWA may have resulted in a forest that is more adapted to these disturbances with respect to the central Amazonia (CA). Increases in the occurrence of windthrows may produce a shift in composition in CA but not in NWA.

Summary
Tree mortality is a key driver of forest community composition and carbon dynamics. Strong winds associated with severe convective storms are dominant natural drivers of tree mortality in the Amazon. Why forests vary with respect to their vulnerability to wind events and how the predicted increase in storm events might affect forest ecosystems within the Amazon are not well understood. The team found that windthrows are common in the Amazon region extending from northwest (Peru, Colombia, Venezuela, and west Brazil) to central Brazil, with the highest occurrence of windthrows in NWA. More frequent winds, produced by more frequent severe convective systems, in combination with well-known processes that limit the anchoring of trees in the soil, help to explain the higher vulnerability of NWA forests to winds. Projected increases in the frequency and intensity of convective storms in the Amazon have the potential to increase wind-related tree mortality. A forest demographic model calibrated for the northwestern and the central Amazon showed that northwestern forests are more resilient to an increase in wind-related tree mortality than forests in the central Amazon. This study emphasizes the importance of including wind-related tree mortality in model simulations for reliable predictions of the future of tropical forests and their effects on the Earth system.

Contacts
BER Program Managers
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Dorothy Koch
SC-23.1
dorothy.koch@science.doe.gov (301-903-0289)

Principal Investigator
Jeffrey Q. Chambers
Lawrence Berkeley National Laboratory
Berkeley, CA 94720
jchambers@lbl.gov

Funding
This research was supported as part of the Next-Generation Ecosystem Experiments (NGEE)–Tropics and the Regional and Global Climate Modeling projects, both funded by the Office of Biological and Environmental Research, within the U.S. Department of Energy, Office of Science.

Publications
Negron-Juarez, R., et al., “Vulnerability of Amazon forests to storm-driven tree mortality.” Environmental Research Letters 13(5), 054021 (2018). [DOI:10.1088/1748-9326/aabe9f]

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


April 30, 2018

Increased Earthworm Density Supports Soil Carbon Storage in a Forest Exposed to Elevated CO2

Carbon isotope analysis tracked carbon transfer from detritus to earthworms, earthworm casts, and soil.

The Science
The density of native earthworms in a sweetgum plantation forest increased in response to the stimulation of fine-root production caused by carbon dioxide (CO2) enrichment of the forest, and the earthworms altered the transfer of carbon from dead plant material to soil.

The Impact
This research has identified earthworm activity as an important mechanism for increased production of soil microaggregates and carbon accrual in response to increasing atmospheric CO2. Carbon accrual in protected soil pools removes carbon from the atmosphere and thereby partially mitigates the increasing concentration in the atmosphere.

Summary
Net primary productivity influences soil food webs and ultimately the amount of carbon inputs in ecosystems. Earthworms can physically protect organic matter from rapid mineralization through the formation of soil aggregates. Previous studies at the Oak Ridge National Laboratory Free Air CO2 Enrichment (FACE) experiment showed that elevated CO2 increased fine-root production and increased soil carbon through soil aggregation. In this project, the role of earthworms in these carbon transfer processes was investigated by tracking the stable carbon isotope signature in leaf litter, fine roots, earthworms, earthworm casts, and bulk soil. The most abundant endogeic (subsurface, organic matter–consuming) earthworm at the FACE site is Diplocardia spp., and its density was positively correlated with production of leaf litter and fine roots in the previous two years. Carbon isotope analysis following termination of the elevated CO2 treatment confirmed that the earthworms were consuming organic matter derived from previous years’ plant detritus. The positive response of earthworms to increased fine-root production, caused by CO2 enrichment, is consistent with the increased soil aggregate formation and increased soil carbon observed in the CO2-enriched plots of the FACE experiment.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Principal Investigators
Yaniria Sánchez-de León
University of Illinois at Chicago and University of Puerto Rico at Mayagüez
yaniria.sanchez@upr.edu

Richard J. Norby
Oak Ridge National Laboratory
Oak Ridge, TN 37831
rjn@ornl.gov

Funding
The Oak Ridge National Laboratory (ORNL) Free Air CO2 Enrichment (FACE) experiment was supported by the Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science. This work was funded by the National Science Foundation (grant # DEB-0919276), the University of Illinois at Chicago (UIC), the UIC Stable Isotope Laboratory, the University of Puerto Rico at Utuado (UPRU), and the University of Puerto Rico at Mayagüez.

Publications
Sánchez-de León, Y. et al. “Endogeic earthworm densities increase in response to higher fine-root
production in a forest exposed to elevated CO2.” Soil Biology and Biochemistry 122, 31–38 (2018). [DOI:10.1016/j.soilbio.2018.03.027]

Related Links
http://face.ornl.gov

Topic Areas:

Division: SC-33 BER


April 15, 2018

Spatio-temporal Convergence of Maximum Daily Light-use Efficiency Based on Radiation Absorption by Canopy Chlorophyll

Advancing the biophysical understanding of satellite estimates of ecosystem-scale maximum daily light-use efficiency.

The Science
Plants absorb light to fix carbon dioxide; the efficiency of this process is termed as light-use efficiency and can be calculated based on different light absorption definitions. Among the light being absorbed by plants, only a fraction is captured by chlorophyll and can be further used for photosynthesis. In this study, scientists from Brookhaven National Laboratory (BNL) used satellite data and derived an estimation of the fraction of light that is absorbed by chlorophyll. The scientists found that different plants have a similar efficiency using chlorophyll absorbed light to fix carbon dioxide; this efficiency is also found to be stable throughout the season in tropical forest. The results of this study can be used to improve models’ capability to estimate the total carbon fixed by plants at global scale.

The Impact
This analysis resolves the much-debated concept of satellite-derived ecosystem-scale maximum daily light-use efficiency by showing a spatio-temporal convergence of maximum daily light-use efficiency based on radiation absorption by canopy chlorophyll. These results of the convergent relationship between ecosystem-scale maximum light-use efficiency and canopy-scale chlorophyll content also provide an improved satellite-based parameterization of large-scale vegetation models to improve the capability to estimate the total carbon fixed by plants at global scale.

Summary
Seasonal variation of ecosystem-scale maximum daily light-use efficiency (approximated by the light-use efficiency under the reference environmental condition) was derived from one eddy covariance tower site, the Tapajos K67 site, in central Amazon. The eddy covariance derived maximum light use efficiency terms (PC) were used as ground truth and then compared with three versions of satellite indices, including Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI), and MERIS Terrestrial Chlorophyll Index (MTCI). Since MTCI is an indicator of canopy-scale chlorophyll content, the close match between the seasonality of MTCI and ecosystem-scale light-use efficiency of the reference environment suggests that satellite-derived canopy-scale chlorophyll content can track the photosynthetic capacity in the tropical forests. The similar finding, but across diverse ecosystems across the globe, is also found in this study. As such, this study demonstrates a convergent relationship between canopy chlorophyll (e.g., satellite-derived MTCI) and maximum daily light-use efficiency across both spatial and temporal scales.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Principal Investigators
Lead author
Jin Wu
Brookhaven National Laboratory
Upton, NY 11973-5000
jinwu@bnl.gov

Institutional contact
Alistair Rogers
Brookhaven National Laboratory
Upton, NY 11973-5000
arogers@bnl.gov

Funding
J. Wu was supported by the Next-Generation Ecosystem Experiments (NGEE)–Tropics project, which is supported by the Office of Biological and Environmental Research within the U.S. Department of Energy Office of Science.

Publications
Zhang Y, Xiao X, Wolf S, Wu J, Wu X, Gioli B, Wohlfahrt G, Cescatti A, van der Tol C, Zhou S, Gough CM, Gentine P, Zhang Y, Steinbrecher R, and Ardo J. "Spatio-temporal convergence of maximum daily light-use efficiency based on radiation absorption by canopy chlorophyll." Geophysical Research Letters 45(8), 3508–3519 (2018). [DOI:10.1029/2017GL076354]

Topic Areas:

Division: SC-33 BER


April 09, 2018

Drought Drives Rapid Shifts in Tropical Rainforest Soil Biogeochemistry and Greenhouse Gas Emissions

Research findings suggest that tropical forest biogeochemistry is more sensitive to climate change than previously believed.

The Science
Increasing frequency of severe droughts in tropical forests is likely to drive changes in the global carbon cycle. The 2015 Caribbean drought impacted carbon cycling directly via altered greenhouse gas emissions and indirectly via lower phosphorus availability, a limiting nutrient to tropical plant growth.

The Impact
The rapid response and slow recovery to drought suggest that tropical forest biogeochemistry is more sensitive to climate change than previously believed, with potentially large direct and indirect consequences for regional and global carbon cycles.

Summary
Climate change models predict more frequent and severe droughts in the humid tropics, but how drought will impact tropical forest carbon and greenhouse gas dynamics is poorly understood. In a recent publication, scientists from the University of California, Berkeley, report the effects of the severe 2015 Caribbean drought on soil moisture, oxygen, phosphorus, and greenhouse gas emissions in a humid tropical forest in Puerto Rico. Drought significantly decreases concentrations of inorganic phosphorus, an element commonly limiting to net primary productivity in tropical forests, and significantly increases organic phosphorus. High-frequency greenhouse gas measurements show varied impacts across topography. Soil carbon dioxide emissions increase by 60% on slopes and 163% in valleys. Methane (CH4) consumption increases significantly during drought, but high CH4 fluxes post drought offset this sink after seven weeks. The rapid response and slow recovery to drought suggest tropical forest biogeochemistry is more sensitive to climate change than previously believed, with potentially large direct and indirect consequences for regional and global carbon cycles.

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Climate and Environmental Sciences Division (SC-23.1)
Terrestrial Ecosystem Science
daniel.stover@science.doe.gov

Principal Investigator
Whendee Silver
University of California, Berkeley
Berkeley, California 94720
wsilver@berkeley.edu

Funding
U.S. Department of Energy grant to W.L.S. (TES-DE-FOA-0000749).
National Science Foundation grant to W.L.S. (DEB-1457805).
National Science Foundation Luquillo Critical Zone Observatory grant (EAR-0722476) to the University of New Hampshire.
National Science Foundation Luquillo Long-Term Ecological Research grant (DEB-0620910) to the University of Puerto Rico.

Publication
O’Connell, C.S., et al. “Drought drives rapid shifts in tropical rainforest soil biogeochemistry and greenhouse gas emissions.” Nature Communications 9, 1348 (2018). [DOI:10.1038/s41467-018-03352-3]

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


April 02, 2018

First Observation of Methane’s Increasing Greenhouse Effect at the Earth’s Surface

Predictions of the direct impacts of greenhouse gases must account for local temperature and humidity conditions.

The Science
Methane traps heat in the atmosphere. For the first time, scientists directly measured the increasing greenhouse effect of methane at the Earth's surface. Measuring the atmospheric absorption of methane is complicated and can be impacted by other gases. The team tracked a rise in the warming effect of methane, one of the most important greenhouse gases for the Earth's atmosphere, over 10 years at a field site in northern Oklahoma.

The Impact
This study offers direct measurements. Such measurements are extremely complex. This study shows increasing methane concentrations are leading to an increasing greenhouse effect in the Earth's atmosphere. It also shows that local temperature and humidity conditions must be taken into account to predict the direct impacts of greenhouse gases. 

Summary
While atmospheric methane concentrations plateaued between 1995 and 2006, they have since increased and are expected to impact the surface energy balance. The relationship between methane radiative forcing and methane mixing ratios has previously only been calculated using radiative transfer models. Methane spectroscopy is complicated, and methane absorption can be impacted by other atmospheric gases, including water vapor. Researchers determined the methane radiative forcing using a large suite of atmospheric observations from more than 10 years of observations at the U.S. Department of Energy's Atmospheric Radiation Measurement facility Southern Great Plains site in Oklahoma. One major advance in this study is that researchers account for the spectroscopic interactions between methane and water vapor as well as the vertical distribution of water vapor. They detected no significant trend in methane forcing before 2007, but found a significant trend after 2007. They also showed that both methane and water vapor contribute significantly to the methane radiative forcing signal.  

Biological and Environmental Research Program Managers
Shaima Nasiri
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Climate and Environmental Sciences Division (SC-23.1)
Atmospheric System Research
shaima.nasiri@science.doe.gov

Sally McFarlane
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Climate and Environmental Sciences Division (SC-23.1)
DOE Atmospheric Radiation Measurement User Facility
sally.mcfarlane@science.doe.gov

Funding
This material is based on work supported by the U.S. Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research, as part of the Atmospheric System Research program, Atmospheric Radiation Measurement (ARM) Program, the Terrestrial Ecosystem Science program, and the ARM aerial facility. Resources of the National Energy Research Scientific Computing Center were used. Work at Lawrence Livermore National Laboratory was performed under the auspices of DOE by Lawrence Livermore National Laboratory. The National Oceanic and Atmospheric Administration’s Global Monitoring Division provided data.

Publications
Feldman, D. R., W. D. Collins, S. C. Biraud, M. D. Risser, D. D. Turner, P. J. Gero, J. Tadic, D. Helmig, S. Xie, E. J. Mlawer, T. Shippert, and M. S. Torn. "Observationally derived rise in methane surface forcing mediated by water vapour trends." Nature Geoscience 11, 238 (2018). [DOI:110.1038/s41561-018-0085-9]

Related Links
Lawrence Berkeley National Laboratory press release: First Direct Observations of Methane's Increasing Greenhouse Effect at the Earth's Surface  

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


March 23, 2018

Teasing Out Molecular Details of Arctic Soil Organic Carbon Degradation under Warming

Pinpointing how fast different organic carbon molecules degrade under warming scenarios.

The Science
The breakdown of organic matter in soils is a critical factor in the release of carbon into the atmosphere as carbon dioxide and methane. Scientists have gained new understanding of how soil organic carbon (SOC) degrades at the molecular scale in the warming soil of the Arctic tundra. Using ultrahigh-resolution mass spectrometry techniques, Oak Ridge National Laboratory (ORNL) and Environmental Molecular Sciences Laboratory (EMSL) collaborators found certain molecular components are disproportionately more susceptible to microbial degradation than others. The researchers developed a biodegradation index to facilitate incorporating these findings into detailed carbon cycle models.

The Impact
Arctic soils contain significant stores of carbon. Integrating new knowledge about the biodegradation of organic matter in these soils into detailed models can improve predictions of global carbon cycling and climate feedbacks.

Summary
Understanding how different organic molecules are degraded in the soil is essential for predicting how greenhouse gas fluxes may respond to global climate change. The rate of microbial SOC degradation is controlled not only by temperature, but also by substrate composition. Using ultrahigh-resolution mass spectrometry at EMSL, a Department of Energy Office of Science user facility, a team of scientists from ORNL, Oakland University, and EMSL determined the susceptibility and compositional changes of dissolved organic carbon in a warming experiment at –2 or 8°C with a tundra soil from the Barrow Environmental Observatory in northern Alaska. Based on their chemical compositions, organic carbon molecular formulas were grouped into nine classes, among which lignin-like compounds dominated both the organic and mineral soils and were the most stable. Organic components such as amino sugars, peptides, and carbohydrate-like compounds were disproportionately more susceptible to microbial degradation than others in tundra soil. The findings suggest that biochemical composition is one of the key factors controlling SOC degradation in Arctic soils and should be considered in global carbon degradation models to improve predictions of Arctic climate feedbacks.

Contacts
BER Program Managers
Daniel Stover and Paul Bayer
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289) and Paul.Bayer@science.doe.gov (301-903-5324)

Principal Investigator
Baohua Gu
Oak Ridge National Laboratory
Oak Ridge, TN 37831
gub1@ornl.gov (865-574-7286)

Funding
The Next-Generation Ecosystem Experiments (NGEE)–Arctic project is supported by the Office of Biological and Environmental Research within the U.S. Department of Energy Office of Science.

Publications
Chen H.M., Z. Yang, R.K. Chu, N. Tolic, L. Liang, D.E. Graham, S.D. Wullschleger, and B. Gu. "Molecular insights into Arctic soil organic matter degradation under warming." Environmental Science & Technology 52(8), 4555-4564 (2018). [DOI:10.1021/acs.est.7b05469].

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


March 10, 2018

Ecological Role of Xylem Refilling in Woody Plants

Xylem embolism refilling and resilience against drought-induced mortality in woody plants: processes and trade-offs.

he Science
This paper provides insights into how embolism repair may have evolved and describes the anatomical and physiological features that are thought to facilitate this process.  A modeling framework was developed to test alternative hypotheses about if, when, and in what ecosystems rapid embolism repair occurs during droughts and emerges as ecologically important.

The Impact
This project proposes a new framework that incorporates embolism repair into the "hydraulic efficiency-safety" spectrum.  The researchers propose a second framework for advancing functional diversity and mortality functions in dynamic vegetation models by describing how vulnerability curves operate in plants that recover from embolism.

Summary
The team reviews and synthesizes current research regarding embolism repair of plant xylem during droughts. Two new frameworks are proposed for developing hypotheses about the physiology and ecology of embolism repair.

A hypothesized conceptual framework proposing how embolism refilling may be an additional strategy to the continuum of hydraulic safety and hydraulic efficiency. For example, plants may have low safety, and a high ability to recover from embolism. Note that capacitance, which acts as a buffer against embolism, may be regarded as one aspect of avoidance, representing an additional strategy. The research team hypothesizes that species may be able to refill embolism, particularly if they are high water users. Species may also be high water users and unable to refill embolism, using other drought avoidance or tolerance strategies. Alternatively, species may be able to refill embolism and have conservative hydraulic strategies.

Contacts
BER Program Managers
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov

Dorothy Koch
SC-23.1
Dorothy.koch@science.doe.gov

Principal Investigator
Thomas L. Powell
Lawrence Berkeley National Laboratory
Berkeley, CA 94720
tlpowell@lbl.gov

Funding
Funding support was provided in full or in part as follows: MZ by Australian Research Council (ARC) Discovery Early Career Researcher Award (DECRA) DE120100518. TK by the Benoziyo Fund for the Advancement of Science; Mr. and Mrs. Norman Reiser, together with the Weizmann Center for New Scientists; and the Edith and Nathan Goldberg Career Development Chair. WRLA by a National Oceanic and Atmospheric Administration (NOAA) Climate and Global Change Postdoctoral fellowship, administered by the University Corporation of Atmospheric Research. JB by the Austrian Science Fund (FWF): M1757-B22 through the Lise Meitner Program. PJH by the University of New Mexico. NKR by the German Federal Ministry of Education and Research (BMBF), through the Helmholtz Association and its research programme ATMO and by the German Research Foundation through its Emmy Noether Programme (RU 1657/2-1). TLP by student research funding from the Department of Organismic and Evolutionary Biology (OEB) and by the Next-Generation Ecosystem Experiments (NGEE)–Tropics project of the Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science. GvA by the Swiss State Secretariat for Education, Research and Innovation SERI (SBFI C14.0104 and C12.0100).  W.R.L.A. acknowledges funding from National Science Foundation 1714972 and from the Agricultural and Food Research Initiative Competitive Program's Ecosystem Services and Agroecosystem Management of the U.S. Department of Agriculture's National Institute of Food and Agriculture (grant no. 2017-05521).

Publications
Klein, T., M.J.B. Zeppel, W.R.L. Anderegg, J. Bloemen, M.G. De Kauwe, P. Hudson, N.K. Ruehr, T.L. Powell, G. von Arx, and A. Nardini. “Xylem embolism refilling and resilience against drought-induced mortality in woody plants: processes and trade-offs.” Ecological Research 33(5), 839–855 (2018). [DOI:10.1007/s11284-018-1588-y]

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


March 04, 2018

Photosynthetic Capacity of Branches Increases During the Dry Season in a Central Amazon Forest

First direct evidence from individual trees that new leaf growth and development cause overall forest green-up.

The Science
Amazon forest ecosystems are observed by satellites to green-up and by flux towers to increase in photosynthetic uptake during the dry season, but the mechanisms for this phenomenon at the tree and leaf scale have been much debated. Here scientists from Brown University and the University of Arizona tested how leaf age–dependent physiology and leaf demography combine to affect photosynthetic capacity of a central Amazon forest during the dry season in a field-based study independent of remote sensing or eddy covariance methods. They found the first direct field evidence that branch-scale photosynthetic capacity increases during the dry season, with a magnitude consistent with increases in ecosystem-scale photosynthetic capacity derived from flux towers.

The Impact
This new study is the first to directly show the mechanistic basis for the much-debated Amazon forest dry season green-up phenomenon. It highlights the role of endogenous phenological rhythms—not just seasonal variation in climate drivers—as a key mechanism regulating the seasonality of photosynthesis. This is important because in most Earth system models (ESMs), the seasonality of tropical evergreen ecosystems is driven by climatic seasonality, not biological phenology, and many of these models do not yet correctly simulate this pattern. This study thus strongly supports the incorporation of leaf phenology into ESMs as a means to represent the best understanding of the key processes regulating photosynthesis.

Summary
The research team conducted demographic surveys of leaf age composition and measured age-dependence of leaf physiology in broadleaf canopy trees of abundant species at a central eastern Amazon site. Using a novel leaf-to-branch scaling approach, they used these data to independently test the much-debated hypothesis—arising from satellite and tower-based observations—that leaf phenology could explain the forest-scale pattern of dry season photosynthesis. They found that photosynthetic capacity, as indicated by parameters of biochemical limitations on photosynthesis [VcmaxJmax, and triose-phosphate utilization (TPU)], was higher in recently matured leaves than in either young or old leaves, and stomatal conductance was higher for recently matured leaves than for old leaves. Most tree branches had several different leaf-age categories simultaneously present, and the number of recently mature leaves on branches of the focal trees increased as the dry season progressed (before October 15 versus after October 15), as old leaves were exchanged for young leaves that then matured. Together, these findings suggest that aggregated whole-branch Vcmax increases during the dry season, with a magnitude consistent with increases in ecosystem-scale photosynthetic capacity observed from flux towers.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Principal Investigator
Lead author  
Loren Albert
Brown University
Providence, RI 02912
loren_albert@brown.edu

Institutional contact
Scott Saleska
University of Arizona
Tucson, AZ 85721
saleska@email.arizona.edu

Funding
This project received U.S. Department of Energy (DOE) support through GoAmazon (award DE-SC0008383). It was also supported by the U.S. National Science Foundation (NSF; award OISE-0730305 to S. Saleska), the Philecology Foundation through University of Arizona Biosphere 2 and a Marshall Foundation of Arizona dissertation fellowship to L.P. Albert. J. Wu was supported in part by the Next-Generation Ecosystem Experiment (NGEE)–Tropics project of the Office of Biological and Environmental Research within the DOE Office of Science.

Publications
Albert, L.P., J. Wu, N Prohaska, P.B. de Camargo, T.E. Huxman, E.S. Tribuzy, V.Y. Ivanov, R.S. Oliveira, S. Garcia, M.N. Smith, RC Oliviera, Jr., N. Restrepo-Coupe, R. da Silva, S.C. Stark, G.A. Martins, D.V. Penha, and S.R. Saleska. "Age-dependent leaf physiology and consequences for crown-scale carbon uptake during the dry season in an Amazon evergreen forest." New Phytologist 219(3), 870–884 (2018). DOI:10.1111/nph.15056]

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


March 02, 2018

Resource Acquisition and Reproductive Strategies of Tropical Forest in Response to the El Niño-Southern Oscillation

Coordination between leaf and fruit phenology driven by a warm phase of ENSO.

The Science   
It has been suggested that tree phenology may be regulated by climatic oscillations. Here, a team a scientists from the Next-Generation Ecosystem Experiments (NGEE)–Tropics project present a 30-year tropical forest dataset that suggests leaf and fruit production is coordinated with El Niño–Southern Oscillation (ENSO) cycles, with greater leaf fall observed prior to El Niño, followed by greater seed production.

The Impact
The response of tropical forest to ENSO events and in general to drought and other environmental stresses is still under exploration. Here, they show a relatively strong response of tropical phenology (fruiting and leafing) to a warming phase of ENSO. This discovery can help in understanding the mechanisms of response or adaptation of plants to climate variability and pave the road to their implementation into Earth Ecosystem Models.

Summary
For the first time an interaction between phenophases of tropical plants (leafing and fruiting) is shown to be driven by large-scale periodic climate variations. This interaction mirrors the dynamics between dry and wet seasons, suggesting adaptive strategies to optimize reproduction and resource acquisition in response to environmental stress.

Contacts
BER Program Managers
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Dorothy Koch
SC-23.1
Dorothy.koch@science.doe.gov (301-903-0105)

Principal Investigator
Matteo Detto
Associate Researcher, Dept. of Ecology and Evolutionary Biology
Princeton University and Smithsonian Tropical Research Institute
mdetto@princeton.edu

Funding
The Environmental Sciences Program of the Smithsonian Institution funded the data collection. M.D. was partially supported by the Next-Generation Ecosystem Experiments (NGEE)–Tropics project. Raul Rios, Brian Harvey, and Steven Paton collected the BCI climate data.

Publications
Detto, M., Wright, S.J., Calderón, O., & Muller-Landau, H.C. "Resource acquisition and reproductive strategies of tropical forest in response to the El Niño-Southern Oscillation." Nature Communications 9, 913 (2018). [DOI:10.1038/s41467-018-03306-9].

Related Links
https://www.nature.com/articles/s41467-018-03306-9

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


March 01, 2018

Rapid Remote Sensing Assessment of Impacts from Hurricane Maria on Forests of Puerto Rico

Scientists can now provide the forest disturbance map and mortality estimation in a short period after the hurricanes.

The Science
Hurricane Maria made landfall as a strong Category 4 storm in southeast Puerto Rico on September 20, 2018. The powerful storm traversed the island in a northwesterly direction causing widespread destruction. Dramatic changes in forest structure across the entire island were evident from pre- and post-Maria composited Landsat 8 images. A non-photosynthetic vegetation (ΔNPV) map for only the forested pixels illustrated significant spatial variability in disturbance, with emergent patterns associated with factors such as slope, aspect, and elevation. An initial order-of-magnitude impact estimate based on remote sensing and previous field work indicated that Hurricane Maria may have caused mortality and severe damage to 23 to 31 million trees. Additional field work and image analyses are required to further detail the impact of Hurricane Maria to Puerto Rico forests.

The Impact
The analyses and results from this work represent a rapid response capability following natural disasters impacting forested ecosystems. Datasets are publicly available, and a set of user interface tools is being developed for a variety of stakeholder end uses.

Summary
Cyclonic storms represent a dominant natural disturbance in temperate and tropical forests in coastal regions of North and Central America. More recently, satellite remote sensing approaches have enabled the spatially explicit mapping of disturbance impacts on forested ecosystems, providing additional insights into the factors of storms. The team generated calibrated and corrected Landsat 8 image composites for the entire island using Google Earth Engine for a comparable pre-Maria and post-Maria time period that accounted for phenology. They carried out spectral mixture analysis (SMA) using image-derived endmembers on both composites to calculate the change in the ΔNPV spectral response, a metric that quantifies the increased fraction of exposed wood and surface litter associated with tree mortality and crown damage from the storm. They produced a ΔNPV map for only the forested pixels illustrated significant spatial variability in disturbance, with emergent patterns associated with factors such as slope, aspect, and elevation. They also conducted hurricane simulations using the Weather Research and Forecasting (WRF) regional climate model to estimate wind speeds associated with forest disturbance.

Contacts
BER Program Managers
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
daniel.stover@science.doe.gov, 301-903-0289

Dorothy Koch
SC-23.1
Dorothy.koch@science.doe.gov (301-903-0105)

Principal Investigator
Jeffrey Chambers
Lawrence Berkeley National Laboratory
jchambers@lbl.gov, 510-495-2932

Lead Author Contact
Yanlei Feng
University of California, Berkeley
Lawrence Berkeley National Laboratory
Berkeley, CA 94720
yanleifeng@lbl.gov

Funding
This research was supported by the Office of Biological and Environmental Research, within the U.S. Department of Energy (DOE) Office of Science, under Contract No. DE-AC02-05CH11231, as part of the Next-Generation Ecosystem Experiments (NGEE)–Tropics project and the Regional and Global Climate Modeling Program. Resources were used from the National Energy Research Scientific Computing Center (NERSC), also supported by the DOE Office of Science under Contract No. DE-AC02-05CH11231.

Publications
Feng, Y., R.I. Negron-Juarez, C.M. Patricola, W.D. Collins, M. Uriarte, J.S. Hall, N. Clinton, and J.Q. Chambers. “Rapid remote sensing assessment of impacts from Hurricane Maria on forests of Puerto Rico.” PeerJ Preprints 6, e26597v1 (2018). [DOI:10.7287/peerj.preprints.26597v1]

Related Links

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


February 26, 2018

Forest Lichens May Suffer Changes in Production and Range with Future Environmental Warming

Empirical and modeling approaches were used to assess the response of lichens as an indicator species for change.

The Science 
The Spruce and Peatland Responses Under Changing Environments (SPRUCE) environmental manipulation experiment funded by the U.S. Department of Energy (DOE) were used to study productivity and community composition of arboreal lichens (those living on tree branches) in a warmer future environment.

The Impact
Changing patterns of warming and drying are likely to decrease or reverse tree-based lichen growth at its southern range margins. Negative carbon balances among persisting individuals could commit these epiphytes to local extinction. These findings illuminate fundamental processes underlying local extinctions of epiphytes and suggest broader consequences for range shrinkage if dispersal and recruitment rates cannot keep pace.

Summary
Changing climates are expected to affect the abundance and distribution of global vegetation, especially plants and lichens with an epiphytic lifestyle and direct exposure to atmospheric variation. The study of epiphytes could improve understanding of biological responses to climatic changes, but only if the conditions that elicit physiological performance changes are clearly defined. The team evaluated individual growth performance of the epiphytic lichen Evernia mesomorpha, an iconic boreal forest indicator species, in the first year of a decade-long experiment featuring whole-ecosystem warming and drying. Field experimental enclosures were located near the southern edge of the species' range.

Mean annual biomass growth of Evernia significantly declined 6 percentage points for every +1°C of experimental warming after accounting for interactions with atmospheric drying. Mean annual biomass growth was 14% in ambient treatments, 2% in unheated control treatments, and –9% to –19% (decreases) in energy-added treatments ranging from +2.25 to +9.00°C above ambient temperatures. Warming-induced biomass losses among persistent individuals were suggestive evidence of an extinction debt that could precede further local mortality events.

Changing patterns of warming and drying would decrease or reverse Evernia growth at its southern range margins, with potential consequences for the maintenance of local and regional populations. Negative carbon balances among persisting individuals could physiologically commit these epiphytes to local extinction. These findings illuminate the processes underlying local extinctions of epiphytes and suggest broader consequences for range shrinkage if dispersal and recruitment rates cannot keep pace.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Principal Investigator
Paul J. Hanson
Environmental Sciences Division, Oak Ridge National Laboratory
Oak Ridge, TN 37831
hansonpj@ornl.gov

Funding
This material is based on work supported by the Office of Biological and Environmental Research, within the U.S. Department of Energy (DOE) Office of Science. Oak Ridge National Laboratory (ORNL) is managed by UT Battelle, LLC, for DOE under contract DEAC05-00OR22725. The SPRUCE experiment is a collaborative research effort between ORNL and the U.S. Department of Agriculture Forest Service.

Publications
Smith, R.J., P.R. Nelson, S. Jovan, P.J. Hanson, and B. McCune. "Novel climates reverse carbon uptake of atmospherically dependent epiphytes: climatic constraints on the iconic boreal forest lichen Evernia mesomorpha." American Journal of Botany 105(2), 266–274 (2018). [DOI:10.1002/ajb2.1022]

Related Links
Spruce and Peatland Responses Under Changing Environments project

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


February 26, 2018

Reforestation can Sequester Globally Significant Amounts of Soil Carbon

Within a century, carbon accumulation in topsoils of U.S. land areas undergoing reforestation could exceed 2 Pg carbon.

The Science
Reforestation of marginal croplands and active replanting on understocked forest lands are two promising strategies for increasing soil carbon sequestration. The rate of carbon accumulation in surface soils of lands already undergoing reforestation in the continental United States was quantified by combining 15,000 soil profile observations with remote sensing and geospatial information.

The Impact
This study provides the first empirical estimate for the role of reforesting topsoils in U.S. forest carbon sequestration. The results suggest that the carbon sink associated with the surface soils of lands currently undergoing reforestation could persist for decades, providing more than 10% of the total forest sector carbon sink through the 21st century.

Summary
Soils can act as either a source or a sink of atmospheric carbon, depending on land use and management. Data associated with 15,000 soil profile observations were integrated with remote sensing and geospatial information to quantify changes in surface soil carbon stocks associated with lands undergoing reforestation across the continental United States. Currently, these reforesting lands occupy >500,000 km2 and accumulate 13 to 21 terragrams of carbon (Tg C) per year in surface soils. Annually, these soil carbon gains represent 10% of the entire forest sector carbon sink, effectively offsetting 1% of all U.S. greenhouse gas emissions. Although the surface soils of existing reforesting lands are projected to sequester a cumulative 1.3 to 2.1 Pg C within a century, additional replanting of understocked forest lands and further efforts to convert marginal cropland to forest could significantly increase forest sector carbon sequestration. This study provides new observational benchmarks to constrain model projections of the role of reforestation in the U.S. carbon budget and the magnitude and longevity of the U.S. forest carbon sink.

Contacts
BER Program Managers
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Renu Joseph
SC-23.1
renu.joseph@science.doe.gov (301-903-9237)

Principal Investigator
Julie D. Jastrow
Argonne National Laboratory
Lemont, IL 60439
jdjastrow@anl.gov (630-252-3226)

Author Contact
Umakant Mishra
Argonne National Laboratory
Lemont, IL 60439
umishra@anl.gov (630-252-1108)

Funding
This study was supported by the U.S. Department of Agriculture Forest Service, Northern Research Station Agreements 13-CR112306-077 and 16-CR-112306-071, National Science Foundation Award EF-1340681, and Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science, under contract DE-AC02-06CH11357.

Publication
Nave, L.E., Domke, G.M., Hofmeister, K.L., Mishra, U., Perry, C.H., Walters, B.F, & Swanston, C.W. "Reforestation can sequester two petagrams of carbon in US topsoils in a century. Proceedings of the National Academy of Sciences USA 115(11), 2776– 2781 (2018). [DOI:10.1073/pnas.1719685115]

Related Links
Argonne National Laboratory News: Locked in a forest

 

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


February 22, 2018

Soil Microbiome in Arctic Polygonal Tundra Unlocked

Landscape topography structures the soil microbiome in Arctic polygonal tundra.

The Science
In the Arctic, environmental factors governing microbial degradation of soil carbon in active layer and permafrost are poorly understood. Here a team of scientists from the Next-Generation Ecosystem Experiments (NGEE)–Arctic project determined the functional potential of soil microbiomes horizontally and vertically across a cryoperturbed polygonal landscape in Barrow, Alaska.

The Impact
The role of ecosystem structure in microbial activity related to greenhouse gas production is poorly understood. Here, the scientists show that microbial communities and ecosystem function vary across fine-scale topography in an Arctic polygonal tundra.

Summary
With comparative metagenomics, genome binning of novel microbes, and gas flux measurements, a team of scientists from the NGEE-Arctic show that microbial greenhouse gas production is strongly correlated to landscape topography. While microbial functions such as fermentation and methanogenesis were dominant in wetter polygons, in drier polygons genes for carbon mineralization and methane (CH4) oxidation were abundant. The active layer microbiome was poised to assimilate nitrogen and not to release nitrous oxide (N2O), reflecting low N2O flux measurements. These results provide mechanistic links of microbial metabolism to greenhouse gas fluxes that are needed for the refinement of model predictions.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov

Principal Investigators
Neslihan Tas
Lawrence Berkeley National Laboratory
Berkeley, CA 94720
ntas@lbl.gov

LBNL POC: Susan Hubbard
Lawrence Berkeley National Laboratory
Berkeley, CA 94720
sshubbard@lbl.gov

Stan Wullschleger
Oak Ridge National Laboratory
Oak Ridge, TN 37831
wullschlegsd@ornl.gov

Funding
The Next-Generation Ecosystem Experiments (NGEE)–Arctic project is supported by the Office of Biological and Environmental Research within the U.S. Department of Energy (DOE) Office of Science. The DOE Joint Genome Institute, a DOE Office of Science user facility, is supported through Contract No. DE-AC0205CH11231 to Lawrence Berkeley National Laboratory.

Publications
Tas, Neslihan, Emmanuel Prestat, Shi Wang, Yuxin Wu, Craig Ulrich, Timothy Kneafsey, Susannah G. Tringe, Margaret S. Torn, Susan S. Hubbard & Janet K. Jansson. "Landscape topography structures the soil microbiome in arctic polygonal tundra." Nature Communications 9, 777 (2018). [DOI:10.1038/s41467-018-03089-z]

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


February 21, 2018

Thermodynamic Links Between Substrate, Enzyme, and Microbial Dynamics

A research team from Lawrence Berkeley National Laboratory (LBNL) presented a mechanistic approach linking temperature dependencies of microbial reactions important in soil biogeochemistry.

The Science
The team introduced a simple but comprehensive mechanistic approach that uses thermodynamics and biochemical kinetics to link reaction rates, Michaelis-Menten constants, biomass yields, mortality rates, and temperature for soil microbes.

The Impact
Accurate prediction of microbially mediated reaction rates is critical for soil biogeochemical models. The team's approach uses thermodynamics and biochemical kinetics to link the dominant controlling factors on these rates, including their temperature dependencies.

Summary
A research team from LBNL introduced a simple but comprehensive mechanistic approach that uses thermodynamics and biochemical kinetics to describe and link microbial reaction rates, Michaelis-Menten constants, biomass yields, mortality rates, and temperature. The temperature control is exerted by catabolic enthalpy at low temperatures and catabolic entropy at high temperatures, whereas changes in cell and enzyme–substrate heat capacity shift the anabolic electron use efficiency and the maximum reaction velocity. The researchers show that cells have optimal growth when the catabolic (differential) free energy of activation decreases the cell free energy harvest required to duplicate their internal structures if electrons for anabolism are available. With the described approach, the team accurately predicted observed glucose fermentation and ammonium nitrification dynamics across a wide temperature range with a minimal number of thermodynamics parameters, and the scientists highlight how kinetic parameters are linked to each other using first principles. These results can inform new microbe-explicit biogeochemistry models, such as those being developed in E3SM.

Contacts
BER Program Manager
Daniel Stover  
Terrestrial Ecosystem Science, SC-23.1
DanielStover@science.doe.gov

Principal Investigator
William J. Riley
Lawrence Berkeley National Laboratory
Berkeley, CA 94720
wjriley@lbl.gov

Funding
This research was supported by the Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science, under contract no. DE-AC02- 05CH11231 as part of the Lawrence Berkeley National Laboratory's Terrestrial Ecosystem Science Scientific Focus Area (SFA) project.

Publications
Maggi, F.M., F.H.M. Tang, and W.J. Riley. "The thermokinetic link between substrate, enzyme and microbial dynamics in Michaeli-Menten-Monod kinetics." International Journal of Chemical Kinetics 50(5), 343–356 (2018). [DOI:10.1002/kin.21163]

 

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


February 20, 2018

An Improved Numerical Method for Solving Depth-Resolved Biogeochemical Models

A method of alternating characteristics with application to advection-dominated environmental systems.

The Science
Scientists at Lawrence Berkeley National Lab (LBNL) propose a numerical integration method, termed the method of alternating characteristics (MAC), to efficiently and accurately solve systems of partial differential equations that arise in modeling environmental processes. They highlight the advantages of MAC with emphasis on advection-dominated environmental systems with biogeochemical reactions.

The Impact
The proposed method is uniquely suited for solving depth-resolved models of advection-dominated environmental systems with biogeochemical reactions and offers advantages in performance over other numerical integration schemes that often require considerable computational resources.

Summary
Here, LBNL scientists present a numerical integration method for solving systems of partial differential equations (PDEs) that arise in modeling environmental processes undergoing advection and biogeochemical reactions. The salient feature of these PDEs is that all partial derivatives appear in linear expressions. As a result, the system can be viewed as a set of ordinary differential equations (ODEs), albeit each one along a different characteristic. The proposed method, termed MAC, then consists of alternating between equations and integrating each one step-wise along its own characteristic, thus creating a customized grid on which solutions are computed. Since the solutions of such PDEs are generally smoother along their characteristics, the method offers the potential of using larger time steps while maintaining accuracy and reducing numerical dispersion. The advantages in efficiency and accuracy of the proposed method are demonstrated in two illustrative examples that simulate depth-resolved reactive transport and soil carbon cycling.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Principal Investigator
William J. Riley
Lawrence Berkeley National Laboratory
Berkeley, CA 94720
wjriley@lbl.gov; 510-495-2223

Funding
This material is based on work supported by the Terrestrial Ecosystem Science Program of the Office of Biological and Environmental Research, within the U.S. Department of Energy (DOE) Office of Science, under contract number DE-AC02-05CH11231. K.G. acknowledges support from the Office of Science Graduate Student Research (SCGSR) program, supported and managed by the DOE Office of Science's Office of Workforce Development for Teachers and Scientists. The SCGSR program is administered by the Oak Ridge Institute for Science and Education (ORISE) for the DOE. ORISE is managed by Oak Ridge Associated Universities under contract number DE-SC0014664.

Publications
Georgiou, K., J. Harte, A. Mesbah, and W. J. Riley. "A method of alternating characteristics with application to advection-dominated environmental systems." Computational Geosciences 22, 851–65 (2018). [DOI:10.1007/s10596-018-9729-5].

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


February 16, 2018

A Challenging Future for Tropical Forests

Mortality rates of moist tropical forests are on the rise due to environmental drivers and related mechanisms.

The Science
Moist tropical forests are the largest terrestrial carbon sink in the world and house most of Earth's terrestrial biodiversity. However, climatic and ecological benefits of intact moist tropical forests face the threat of increasing tree mortality due to environmental and biotic changes. A Pacific Northwest National Laboratory scientist led a study to determine the risks of increasing tropical forest tree mortality. In this study, scientists reviewed the state of knowledge regarding moist tropical forest tree mortality. They created a conceptual framework with testable hypotheses regarding the drivers, mechanisms, and interactions that may underlie increasing mortality rates of moist tropical forests. The research team then identified next steps for improved understanding and reduced predictive uncertainty.

The Impact
Researchers found that mortality rates of trees in moist tropical forests are increasing as the drivers and mechanisms of tree mortality—such as temperature, drought, and carbon dioxide (CO2)—continue to rise. These effects are expected to continue increasing under future environmental conditions, with serious consequences to Earth's carbon cycle.

Summary
Tropical forests absorb a significant amount of atmospheric CO2. Tree death reverses this process by shutting off photosynthesis and increasing carbon release (from dead wood), leaving more CO2 in the atmosphere. Increasing tree mortality rates observed over the past few decades in moist tropical forests are associated with rising temperature, vapor pressure deficit, liana (woody vine) abundance, drought, wind events, fire, and possibly CO2 fertilization–induced increases in stand thinning. Most of these mortality drivers ultimately kill trees in part through carbon starvation and hydraulic failure, though the relative importance of each driver is unknown. Ecosystems with greater diversity may buffer tropical forests against large-scale mortality events, but recent and expected trends in mortality drivers are likely to continue or increase. Model predictions of tropical tree mortality are rapidly improving, but they require more empirical knowledge regarding the most common drivers and their subsequent mechanisms. This study identified critical hypotheses, datasets, and model developments required to quantify the underlying causes of increasing mortality rates and to improve predictions of future mortality and carbon storage consequences under environmental change.

Contacts
BER Program Manager
Dan Stover
Terrestrial Ecosystem Science, 23.1
Daniel.Stover@science.doe.gov

Principal Investigator
Nate McDowell
Pacific Northwest National Laboratory
Richland, WA 99354
nate.mcdowell@pnnl.gov

Funding
This manuscript is the product of the workshop “Tropical forest mortality” held in Santa Fe, New Mexico, in 2015. The U.S. Department of Energy Office of Science supported the workshop and the writing of the manuscript as part of the Next-Generation Ecosystem Experiments (NGEE)–Tropics project.

Publication
N.G. McDowell et al., “Drivers and Mechanisms of Tree Mortality in Moist Tropical Forests.” New Phytologist (early view, February 16, 2018) 219(3), 851–869 (2018). [DOI:10.1111/nph.15027].

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


January 22, 2018

Optimal Foraging: How Soil Microbes Adapt to Nutrient Constraints

Understanding how microbial communities adjust to nutrient-poor soils at the genomic and proteomic level gives scientists insights into land use and terrestrial biosphere modeling.

The Science
The vital growth nutrient, phosphorus, is scarce in many tropical ecosystems, yet microbes in tropical soils thrive. New research from a team of scientists has now revealed at the genomic and proteomic level how these microbes acquire rare nutrients.

The Impact
This study provides insights into soil microbial communities and how they adapt to different levels of nutrients available in a tropical rainforest. Significant changes in metabolic capabilities, shifts in community structure, and regulation of enzyme abundances revealed how soil microbes adapt to limited nutrients in tropical soils. These findings could have important implications for enhancing agricultural crops and for modeling terrestrial processes and elemental cycles.

Summary
A team of scientists set out to determine whether the theory of optimal foraging, which suggests any ecological community will adjust its consumption strategy to balance the distribution of the life-sustaining elements, applied to microorganisms in soils. While the theory had been applied to plants and animals, which can be easily observed, it is more difficult to apply to tiny, unseen microbes. Scientists from Oak Ridge National Laboratory (ORNL) and The University of Tennessee, Knoxville, gathered samples from a 17-year fertilization experiment of the Smithsonian Tropical Research Institute in Panama. Samples included phosphorus-rich and phosphorus-deficient soil. The advanced Fourier-Transform Ion Cyclotron Resonance Mass Spectrometer at the Environmental Molecular Sciences Laboratory (EMSL), a U.S. Department of Energy (DOE) Office of Science user facility, provided the team with spectra that enabled the scientists to look at samples containing soil organic matter in ways that enabled them to understand what organic compounds were available to the microbes. The Joint Genome Institute (JGI), also a DOE Office of Science user facility, helped team members probe microbial genes in the samples, and the scientists used mass spectrometers at ORNL to identify more than 7,000 proteins in each soil sample. What the researchers found closely matched their theories. The microbes in the two types of soils used different foraging strategies and adjusted their allocation of different genes and proteins to make the most of the scarce phosphorus resources in their environment. Scientists also identified differences in genes associated with the use of carbon, nitrogen, and sulfur. These results could help scientists understand how to better model microbial communities, plan for optimal land use, and predict changes in the Earth system.

Contacts
BER Program Manager 
Paul Bayer,
Subsurface Biogeochemical Research, SC-23.1
301-903-5324

Principal Investigator
Chongle Pan
Oak Ridge National Laboratory
Oak Ridge, TN 37831
panc@ornl.gov

Funding
This work was supported by the Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science, including support of the Environmental Molecular Sciences Laboratory (EMSL) and the Joint Genome Institute (JGI), both DOE Office of Science user facilities, and Laboratory Directed Research and Development funding from Oak Ridge National Laboratory.

Publication
Qiuming, Y., L. Zhou, Y. Song, S.J. Wright, X. Guo, S.G. Tringe, M.M. Tfaily, L. Pasa-Tolic, T.C. Hazen, B.L. Turner, M.A. Mayes, and C. Pan. “Community proteogenomics reveals the systemic impact of phosphorus availability on microbial functions in tropical soil.”  Nature Ecology and Evolution 2, 499–509 (2018). [DOI:10.1038/s41559-017-0463-5]

Related Links
Optimal Foraging:  How Soil Microbes Adapt to Nutrient Constraints on EMSL’s website.
Researchers reveal how microbes cope in phosphorus-deficient tropical soil Oak Ridge National Laboratory news release.

Topic Areas:

Division: SC-33 BER


January 08, 2018

Impacts of Microtopographic Snow Redistribution and Lateral Subsurface Processes in an Arctic Polygonal Ecosystem

Lateral subsurface hydrologic and thermal processes were explicitly represented in the E3SM Land Model.

The Science   
A novel analysis of the impact of snow redistribution and lateral subsurface processes on hydrologic and thermal states at a polygonal tundra site near Utqiagvik (Barrow), Alaska.

The Impact
The research demonstrates the importance of including accurate surface distribution of snow in models to simulate the temperature of subsurface soil temperature and moisture, both vertically and horizontally, during winter and into the warmer seasons.

Summary
Current land surface models, including the Energy Exascale Earth System Model (E3SM) Land Model v1 (ELMv1), are inadequate to capture landscape heterogeneity due to microtopographic features in the Alaskan Arctic costal plan. A team led by Lawrence Berkeley National Laboratory extended the ELM to redistribute incoming snow by accounting for microtopography and incorporated subsurface lateral transport of water and energy. The spatial heterogeneity of snow depth during the winter due to snow redistribution generated surface soil temperature heterogeneity that propagated in depth and time. Excluding lateral subsurface hydrologic and thermal processes led to an overestimation of spatial variability in soil moisture and soil temperature as subsurface liquid pressure and thermal gradients were artificially prevented from spatially dissipating over time. This work also demonstrates an important three-dimensional modeling capability integrated in the global-scale land model ELMv1.

Contacts
BER Program Managers
Dorothy Koch and Daniel Stover  
SC-23.1
Dorothy.Koch@science.doe.gov (301-903-0105)
DanielStover@science.doe.gov (301-903-0289)

Principal Investigator
William J. Riley
Lawrence Berkeley National Laboratory
Berkeley, CA 94720
wjriley@lbl.gov

Funding
This research was supported by the Office of Biological and Environmental Research, within the U.S. Department of Energy (DOE) Office of Science, of under Contract No. DE-AC02- 05CH11231 as part of the Next-Generation Ecosystem Experiments (NGEE)–Arctic and Energy Exascale Earth System Model (E3SM) programs.

Publications
Bisht, G., Riley, W. J., Wainwright, H. M., Dafflon, B., Fengming, Y., and Romanovsky, V. E. "Impacts of microtopographic snow redistribution and lateral subsurface processes on hydrologic and thermal states in an Arctic polygonal ground ecosystem: A case study using ELM-3D v1.0, Geoscientific Model Development 11, 61–76 (2018). [DOI:10.5194/gmd-11-61-2018].

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


January 05, 2018

Drought-Pathogen Interactions and Oak Tree Mortality

Interactions between drought and pathogens are important factors driving “pulses” of oak tree mortality.

The Science
Drought-stress disrupts tree function and growth and is an important factor that can lead to tree mortality. When under stress and weakened, trees are susceptible to infection by opportunistic pathogens that are able to further disrupt tree function. In the Ozark Border Region of central Missouri, there was a severe drought in 2012 that was followed by significant mortality of white oaks (Quercus alba L.; 10.0% of live stems) and black oaks (Q. velutina Lam.; 26.5% of live stems) in the year after. This was surprising because oaks are comparatively drought tolerant and implied that some other factor may be at play. A synthesis of forest inventory data, ecosystem fluxes (with supporting biological observations), tree-ring analyses, and documentation of a pathogen (Biscogniauxia spp., formerly hypoxylon) infection was therefore completed to better understand whether drought-pathogen interactions are important aspects of tree mortality and stand dynamics in this region.

The Impact
Large-scale oak mortality events have been documented in the forest-grasslands transition zone of the Central United States following intense drought conditions. Rising temperatures and changing patterns of precipitation are expected to intensify droughts and make them more lethal. It is therefore critical to better understand how droughts affect tree growth and mortality. The interactions between drought and pathogens have been understudied but are crucial toward more fully understanding how tree mortality rates may change under different environmental conditions. This research points to the significance of event-based oak mortality and that drought-Biscogniauxia interactions are important in shaping oak stand dynamics in this region and underscores the pressing need for more in-depth studies focused on drought-pathogen interactions.

Summary
Stand dynamics were consistent with expected patterns of decreasing tree density but increasing basal area. Basal area growth outpaced mortality, implying a net accumulation of live biomass, which was supported by eddy covariance ecosystem carbon flux observations. There was a threshold response in white and black oak trees to water stress in the previous year, giving rise to significantly elevated mortality in the year after. Individual white and black oaks that died in 2013 displayed historically lower growth with the majority of dead trees exhibiting Biscogniauxia cankers. Taken together, the synthesis points to the importance of drought-pathogens being important drivers of oak mortality “pulses” and thus stand dynamics in these forests.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Principal Investigators
Jeff Wood, Assistant Research Professor
University of Missouri
Columbia, MO 65211
woodjd@missouri.edu (573-882-3295)

Lianhong Gu, Distinguished Scientist
Oak Ridge National Laboratory
Oak Ridge, TN 37831
lianhong-gu@ornl.gov (865-241-5925)

Funding
The Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science, and  the U.S. Department of Agriculture National Institute of Food and Agriculture's McIntire-Stennis funds.

Publications
Wood, J. et al. “The importance of drought-pathogen interactions in driving oak mortality events in the Ozark Border Region.” Environmental Research Letters 13(1), 015004 (2018). [DOI:10.1088/1748-9326/aa94fa]

Related Links
(Reference link)

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER


January 02, 2018

Tropical Forest Soil Carbon Stocks Predicted by Nutrients and Roots, not Aboveground Plant Biomass

Soil base cation availability regulates tropical soil carbon stocks via a negative relationship with fine root biomass.

The Science   
Scientists at the University of California, Los Angeles (UCLA), and the Smithsonian Institution conducted an extensive study of predictors of tropical soil carbon stocks to 1 m depth at 48 sites in Panama, including measurements of soil characteristics, plant biomass, and climate. The study revealed a nearly three-fold change in soil carbon stocks across five soil orders, with soil characteristics like fine root biomass, clay content, and nutrient base cations the strongest predictors of soil carbon stocks.

The Impact
Tropical forests are the most carbon rich ecosystems on Earth, containing 25% to 40% of global terrestrial carbon stocks. Quantification of aboveground biomass in tropical forests has improved recently, but soil carbon dynamics remains one of the largest sources of uncertainty in Earth system models. Including soil base cations in carbon cycle models, and thus emphasizing mechanistic links among nutrients, root biomass, and soil carbon stocks, will improve prediction of climate-soil feedbacks in tropical forests.

Summary
Overall, soil characteristics were the best predictors of soil carbon stocks, with no relationship to aboveground plant biomass or litterfall. The best fit model for the study's data suggested that available base cations provide an indirect control over tropical soil carbon stocks via a negative relationship with fine-root biomass. Soil clay content and rainfall also emerged as significant predictors of soil carbon. In addition to the nearly three-fold change in soil carbon stocks, the sites used here covered five soil orders, over 25 geological formations, a two-fold range in rainfall, a 20-fold range in base cations, and a 100-fold range in available phosphorus. Thus, although the data come from a relatively restricted geographic region, the diversity of environmental conditions means that the results are likely to be broadly applicable over much larger geographical ranges.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Principal Investigator
Daniela F Cusack
Assistant Professor, Department of Geography
University of California, Los Angeles
Los Angeles, CA 90095
dcusack@geog.ucla.edu

Funding
Funding was provided by the National Science Foundation (NSF) GSS Grant #BCS-1437591 and the U.S. Department of Energy (DOE) Office of Science Early Career Research Program Grant DE-SC0015898 to D. F. Cusack, and UK Research and Innovation's National Environment Research Council (NERC) Grant NE/J011169/1 to O. T. Lewis.

Publications
Cusack D.F. et al. “Soil carbon stocks across tropical forests of Panama regulated by base cation effects on fine roots.” Biogeochemistry 137, 253–66 (2018). [DOI:10.1007/s10533-017-0416-8]

Related Links
Complete data on location, rainfall, geology, soil, litterfall, aboveground and root biomass in 48 plots in central Panama, excel format

Topic Areas:

Division: SC-33.1 Earth and Environmental Sciences Division, BER