September 06, 2017

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

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.

Principal Investigator

Alistair Rogers
Brookhaven National Laboratory
arogers@bnl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.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.

References

Rogers, A., Serbin, S. P., Ely, and K. S., Sloan, et al. "Terrestrial biosphere models underestimate photosynthetic capacity and CO2 assimilation in the Arctic". New Phytologist 216 (4), 1090–1103  (2017). https://doi.org/10.1111/nph.14740.