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PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

Terrestrial Biosphere Models Underestimate Photosynthetic Capacity and CO2 Assimilation in the Arctic

Alistair Rogers

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June 9, 2017

New measurements of photosynthesis in the Arctic demonstrate that current models underestimate key photosynthetic parameters and the potential for CO2 uptake by Arctic vegetation.

The Science
Carbon uptake and loss from the Arctic is highly sensitive to climate change, and these processes are poorly represented in terrestrial biosphere models (TBMs). Uncertainty surrounding the Arctic carbon cycle is dominated by uncertainty over carbon dioxide (CO2) uptake by photosynthesis. However, current TBMs have almost no data on Arctic photosynthesis and currently rely on understanding developed in temperate systems. This study provided the first Arctic dataset of the key photosynthetic parameters maximum carboxylation capacity and maximum electron transport rate (known as Vcmax and Jmax, respectively). The scientists found that current TBM representation of these two parameters was markedly lower than the values they measured on the coastal tundra of northern Alaska, in some cases fivefold lower. On average, the capacity for CO2 uptake by Arctic vegetation is double current TBM estimates.

The Impact
This work highlights the poor representation of Arctic photosynthesis in terrestrial biosphere models and provides the critical data necessary to improve the ability to project the response of the Arctic to global environmental change.

Summary
The team measured Vcmax and Jmax in seven species representative of the dominant vegetation found on the coastal tundra near Barrow, Alaska. They made three key discoveries: (1) The temperature-response functions of Vcmax and Jmax that are used to determine how the capacity for CO2 uptake changes with temperature were markedly different than the temperature-response functions of temperate plants. (2) Vcmax and Jmax were two- to fivefold higher than the values used to parameterize current TBMs. (3) Current parameterization of TBMs resulted in a twofold underestimation of the capacity for leaf-level CO2 assimilation in Arctic vegetation. The insight and data set provided in this study can be used to markedly improve TBM representation of Arctic photosynthesis and improve projections of how Arctic photosynthesis responds to rising temperature and CO2 concentration. The high-impact dataset generated during this study has already been used in four additional publications.

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

Principal Investigator
Alistair Rogers
Brookhaven National Laboratory
Upton, NY 11973-5000
arogers@bnl.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 Office of Science.

Publications
Primary publication
Rogers, A., Serbin, S.P., Ely, K.S., Sloan, V.L., Wullschleger, S.D. "Terrestrial biosphere models underestimate photosynthetic capacity and CO2 assimilation in the Arctic." New Phytologist 216(4), 1090–1103 (2017). [DOI:10.1111/nph.14740]

Additional publications that used data from this study
Ghimire B, Riley WJ, Koven CD, Kattge J, Rogers A, Reich PB, Wright IJ. "A global trait-based approach to estimate leaf nitrogen functional allocation from observations." Ecological Applications. 27(5), 1421–1434 (2017). [DOI:10.1002/eap.1542]

De Kauwe MG, Lin Y-S, Wright IJ, Medlyn BE, Crous KY, Ellsworth DE, Maire V, Prentice IC, Atkin OK, Rogers A, Niinemets U, Serbin S, Meir P, Uddling J, Togashil HF, Tarainen L, Weerasinghe LK, Evans BJ, Ishida FY, Domingues TF. "A test of the "one-point method" for estimating carboxylation capacity from field-measured, light-saturated photosynthesis." New Phytologist 210(3), 1130–44 (2016). [DOI:10.1111/nph.13815]

Ali AA, Xu C, Rogers A, Fisher RA, Wullschleger SD, McDowell NG, Massoud EC, Vrugt JA, Muss JD, Fisher JR, Reich PB, Wilson CJ. "A global scale mechanistic model of photosynthetic capacity (LUNA V1.0)." Geoscientific Model Development 9(2), 587–606 (2016). [DOI:10.5194/gmd-9-587-2016]

Ali AA, Xu C, Rogers A, McDowell NG, Medlyn BE, Fisher R, Wullschleger SD, Reich PR, Vrugt JA, Bauerle WL, Santiago LS, Wilson CJ. "Global scale environmental control of plant photosynthetic capacity." Ecological Applications 25(8), 2349–2365 (2015). [DOI:10.1890/14-2111.1]

This work was supported by the Next-Generation Ecosystem Experiments (NGEE Arctic) project that is supported by the Office of Biological and Environmental Research in the Department of Energy, Office of Science.

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