BER Research Highlights

Search Date: December 19, 2018

18 Records match the search term(s):


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 from 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
The problem of including processes such as growth and mortality of individual trees is needed if we are 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 PM)
Daniel Stover
Terrestrial Ecosystem Science
Daniel.Stover@science.doe.gov

Dorothy Koch
Earth System Modeling
Dorothy.koch@science.doe.gov

Renu Joseph
Regional and Global Climate Modeling
renu.joseph@science.doe.gov

(PI Contact)
Rosie Fisher
National Center for Atmospheric Research
rfisher@ucar.edu

Charles Koven
Lawrence Berkeley National Laboratory
cdkoven@lbl.gov

Funding
CDK, BC, RK, JH, TP, JS, CX & SPS were supported by the Next-Generation Ecosystem Experiments (NGEE-Tropics) project that is supported by the Office of Biological and Environmental Research in the 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, T. L., 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 (2017). [DOI: 10.1111/gcb.13910]

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, 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-23.1 Climate 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 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 northwest Amazon. 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 the northwest Amazon forests to winds.

The Impact
The higher frequency of windthrows in the northwestern Amazon (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. We 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 the northwest Amazon. 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 the northwest Amazon 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 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 PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

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

(PI Contact)
Jeffrey Q. Chambers, Lawrence Berkeley National Laboratory
jchambers@lbl.gov

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

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

Topic Areas:

Division: SC-23.1 Climate 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 degrades at the molecular scale in the warming soil of the Arctic tundra. Using ultrahigh-resolution mass spectrometry techniques, ORNL and 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 soil organic carbon (SOC) degradation is controlled not only by temperature but also by substrate composition. Using ultrahigh-resolution mass spectrometry at the Environmental Molecular Sciences Laboratory (EMSL), a DOE Office of Science User Facility, a team of scientists from Oak Ridge National Laboratory, 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 PM)
Daniel Stover and Paul Bayer
SC-23.1
Daniel.Stover@science.doe.gov and Paul.Bayer@science.doe.gov  

(PI Contact)
Baohua Gu
Oak Ridge National Laboratory
gub1@ornl.gov

Funding
The Next-Generation Ecosystem Experiments (NGEE Arctic) project is supported by the Office of Biological and Environmental Research in the DOE 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-23.1 Climate 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.

The 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 paper proposes a new framework that incorporates embolism repair into the ‘hydraulic efficiency-safety’ spectrum.  This paper 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
This paper 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/tolerance strategies. Alternatively, species may be able to refill embolism and have conservative hydraulic strategies.

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

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

(PI Contact)
Thomas L. Powell
Lawrence Berkeley National Laboratory
tlpowell@lbl.gov

Funding
Funding support was provided in full or in part as follows: MZ by ARC 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 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 OEB department at Harvard University and by the Office of Biological and Environmental Research, US Department of Energy, NGEE Tropics project. 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 NSF 1714972 and from the USDA National Institute of Food and Agriculture, Agricultural and Food Research Initiative Competitive Programme, Ecosystem Services and Agroecosystem Management, 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. (2018).  [DOI: 10.1007/s11284-018-1588-y]

Topic Areas:


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, 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 Earth system models as a means to represent our 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 this 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 (Vcmax, Jmax, and TPU), was higher in recently matured leaves than either young or old leaves, and stomatal conductance was higher for recently matured leaves than old leaves. Most tree branches had several different leaf age categories simultaneously present, and the number of recently mature leaves on branches of our 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 PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov

(PI Contact)
Lead author contact information 
Loren Albert
Brown University
loren_albert@brown.edu

Institutional contact 
Scott Saleska 
University of Arizona 
saleska@email.arizona.edu 

Funding
This project received U.S. 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 DOE’s Office of Biological and Environmental Research.

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, R.C. Oliviera, Jr., N. Restrepo-Coupe, R. da Silva, S.C. Stark, G.A. Martins, D.V. Penha, 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, 870-884 (2018). [DOI: 10.1111/nph.15056]

Topic Areas:


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 of scientists from the NGEE-Tropics project present a 30-year tropical forest dataset that suggests leaf and fruit production is coordinated with ENSO cycles, with greater leaf fall observed prior to El Niño followed by greater seed production.

The Impact
The response of tropical forests to ENSO events and, in general, to drought and other environmental stress, are 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 to understand 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 season, suggesting adaptive strategies to optimize reproduction and resource acquisition in response to environmental stress.

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

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

(PI Contact)
Matteo Detto
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 data collection. M.D. was partially supported by the US Department of Energy Office of Science NGEE-Tropics. Raul Rios, Brian Harvey, and Steven Paton collected the BCI climate data.  

Publications
Detto, M., S.J. Wright, O. Calderón, O. and H.C. Muller-Landau. “Resource acquisition and reproductive strategies of tropical forest in response to the El Niño-Southern Oscillation.” Nature Communications 9, No. 913 (2018). [DOI:10.1038/s41467-018-03306-9]

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

Topic Areas:


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 20th, 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 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 23-31 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 non-photosynthetic vegetation (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 PM)
Daniel Stover
SC-23.1
daniel.stover@science.doe.gov

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

(PI Contact)
Jeffrey Chambers
Lawrence Berkeley National Laboratory
jchambers@lbl.gov

(Lead Author Contact)
Yanlei Feng
Lawrence Berkeley National Laboratory and UC Berkeley
yanleifeng@lbl.gov

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


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 environmental manipulation experiment funded by DOE was 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 PM)
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Paul J. Hanson
Environmental Sciences Division, Oak Ridge National Laboratory
hansonpj@ornl.gov

Funding
This material is based on work supported by the US Department of Energy, Office of Science, Office of Biological and Environmental Research. Oak Ridge National Laboratory (ORNL) is managed by UT Battelle, LLC, for the US Department of Energy under contract DEAC05-00OR22725. The SPRUCE experiment is a collaborative research effort between ORNL and the USDA 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, 266-274 (2018). [DOI:10.1002/ajb2.1022]

Related Links
Spruce and Peatland Responses Under Changing Environments project

Topic Areas:

Division: SC-23.1 Climate 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 C.

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 U.S. 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 either as a source or sink of atmospheric carbon depending upon 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 U.S. Currently, these reforesting lands occupy >500,000 km2 and accumulate 13-21 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 1.3-2.1 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 PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

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

(PI Contact)
Julie D. Jastrow
Argonne National Laboratory
jdjastrow@anl.gov (630-252-3226)

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

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

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

Related Links
ANL Press Release: Locked in a forest

Topic Areas:


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 (C) in active layer and permafrost are poorly understood. Here a team of scientists from NGEE-Arctic 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, they 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 Next Generation Ecosystem Experiment (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 C mineralization and CH4 oxidation were abundant. The active layer microbiome was poised to assimilate N and not to release N2O, reflecting low N2O flux measurements. These results provide mechanistic links of microbial metabolism to GHG fluxes that are needed for the refinement of model predictions.

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

(PI Contact)
Author: Neslihan Tas
Lawrence Berkeley National Laboratory
ntas@lbl.gov

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

PI: Stan Wullschleger
Oak Ridge National Laboratory
wullschlegsd@ornl.gov 

Funding
The Next-Generation Ecosystem Experiments (NGEE Arctic) project is supported by the Office of Biological and Environmental Research in the DOE Office of Science. The Department of Energy Joint Genome Institute, a DOE Office of Science User Facility, is supported through contract number 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, article 777 (2018). [DOI:10.1038/s41467-018-03089-z]

Topic Areas:

Division: SC-23.1 Climate 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. Our 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. We 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, we accurately predicted observed glucose fermentation and ammonium nitrification dynamics across a wide temperature range with a minimal number of thermodynamics parameters, and we 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 PM)
Daniel Stover  
SC-23.1
DanielStover@science.doe.gov

(PI Contact)
William J. Riley
Lawrence Berkeley National Laboratory
wjriley@lbl.gov

Funding
This research was supported by the Office of Science, Office of Biological and Environmental Research of the US Department of Energy under contract no. DE-AC02- 05CH11231 as part of the LBNL TES Scientific Focus Area project.

Publications
Maggi, F. M., F. H. M. Tang, and W. J. Riley. “The thermodynamic links between substrate, enzyme, and microbial dynamics in Michaelis-Menten-Monod kinetics.” International J. of Chemical Kinetics 50(5): 343-356 (2018). [DOI:10.1002/kin.21163]

Topic Areas:


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 the 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 the method of alternating characteristics (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 PM)
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
William J. Riley
Lawrence Berkeley National Laboratory
wjriley@lbl.gov; 510-495-2223

Funding
This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science Program, under contract number DE-AC02-05CH11231. K.G. acknowledges support from the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists, Office of Science Graduate Student Research (SCGSR) program. The SCGSR program is administered by the Oak Ridge Institute for Science and Education (ORISE) for the DOE. ORISE is managed by ORAU 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, (2018). [DOI:10.1007/s10596-018-9729-5]

Topic Areas:

Division: SC-23.1 Climate 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—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 carbon dioxide. Tree death reverses this process by shutting off photosynthesis and increasing carbon release (from dead wood), leaving more carbon dioxide 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 carbon dioxide 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, data sets, 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 PM)
Dan Stover
Terrestrial Ecosystem Science
Daniel.Stover@science.doe.gov

(PI Contact)
Nate McDowell
Pacific Northwest National Laboratory
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 Experiment-Tropics project

Publication McDowell, N.G. et al., "Drivers and Mechanisms of Tree Mortality in Moist Tropical Forests." New Phytologist, 2/16/18 early view (2018). [DOI:10.1111/nph.15027]

Topic Areas:

Division: SC-23.1 Climate 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 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 Oak Ridge National Laboratory 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.

BER PM Contact
Paul Bayer,
Subsurface Biogeochemical Research
SC-23.1, 301-903-5324

PI Contact
Chongle Pan
Oak Ridge National Laboratory
panc@ornl.gov

Funding
This work was supported by the U.S. Department of Energy’s Office of Science, Office of Biological and Environmental Research, 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-23.1 Climate and Environmental Sciences Division, BER



Scientists are studying how microbes in soil use nutrients like phosphorus at the molecular level, helping better model efficient land use and terrestrial processes.



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 in order 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 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 3D modeling capability integrated in the global-scale land model ELMv1.

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

(PI Contact)
William J. Riley
Lawrence Berkeley National Laboratory
wjriley@lbl.gov

Funding
This research was supported by the Director, Office of Science, Office of Biological and Environmental Research of the US Department of Energy under contract no. DE-AC02- 05CH11231 as part of the NGEE-Arctic and Energy Exascale Earth System Model (E3SM) programs.

Publications
Bisht, G., W.J. Riley, H.M. Wainwright, B. Dafflon, Y. Fengming, and V.E. Romanovsky. "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." Geosci. Model Dev. 11, 61-76, (2018). [DOI:10.5194/gmd-11-61-2018]

Reference

Topic Areas:


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 towards 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, our synthesis points to the importance of drought-pathogens being important drivers of oak mortality “pulses” and thus stand dynamics in these forests.

PI Contacts
Jeff Wood
Assistant Research Professor
University of Missouri, MO
woodjd@missouri.edu / 1-573-882-3295

Lianhong Gu
Distinguished Scientist
Oak Ridge National Laboratory, Oak Ridge, TN
lianhong-gu@ornl.gov / 1-865-241-5925 (PI).

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

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

Publications
Wood, J., B.O. Knapp, R-M. Muzika, M.C. Stambaugh, and L. Gu. “The importance of drought-pathogen interactions in driving oak mortality events in the Ozark Border Region.” Environmental Research Letters, 13: 015004 (2018). [DOI: 10.1088/1748-9326/aa94fa]

Related Links
(Reference link)

Topic Areas:


January 02, 2018

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

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

The Science
Scientists at UCLA and the Smithsonian conducted an extensive study of predictors of tropical soil C 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 C stocks across five soil orders, with soil characteristics like fine root biomass, clay content, and nutrient base cations the strongest predictors of soil C stocks.

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

Summary
Overall, soil characteristics were the best predictors of soil C stocks, with no relationship to aboveground plant biomass or litterfall. The best fit model for our data suggested that available base cations provide an indirect control over tropical soil C stocks via a negative relationship with fine root biomass. Soil clay content and rainfall also emerged as significant predictors of soil C. In addition to the nearly three-fold change in soil C 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 P. 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 PM)
Daniela F Cusack
Assistant Professor, Department of Geography, UCLA
dcusack@geog.ucla.edu

(PI Contact)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Funding
Funding was provided by NSF GSS Grant #BCS-1437591 and DOE Office of Science Early Career Research Program Grant DE-SC0015898 to D. F. Cusack, and NERC Grant NE/J011169/1 to O. T. Lewis.

Publications
Cusack D.F., L. Markesteijn, R. Condit, O.T. Lewis, B.L. Turner. “Soil carbon stocks across tropical forests of Panama regulated by base cation effects on fine roots.” Biogeochemistry (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: