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

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 V_cmax and J_max, 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 V_cmax and J_max 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 V_cmax and J_max 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) V_cmax and J_max 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.

Principal Investigator(s)

Alistair Rogers
Brookhaven National Laboratory
[email protected]

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.

References

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]

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]