Terrestrial Biosphere Models May Overestimate Arctic CO₂ Assimilation if They Do Not Account For the Effect of Low Temperature on Photosynthesis

The Science

Terrestrial biosphere models (TBMs) assume that the amount of carbon dioxide (CO₂) taken up by plants per unit of light absorbed (quantum yield) is a global constant. This study found that in Arctic vegetation, growing at low temperature, the quantum yield is reduced, limiting the capacity for CO₂ assimilation at low light levels.

The Impact

If TBMs do not account for the reduction in quantum yield at low temperature, they could overestimate the capacity of Arctic ecosystems to take up CO₂ when light is limiting photosynthesis.

Summary

How TBMs represent leaf photosynthesis and its sensitivity to temperature are two critical components of understanding and predicting the response of the Arctic carbon cycle to global change. Scientists at Brookhaven National Laboratory measured the effect of temperature on the response of photosynthesis to light in six Arctic plant species and determined the quantum yield of CO₂ fixation and the convexity factor, which further describes the response of photosynthesis to light. They also determined leaf absorptance to calculate quantum yield on an absorbed light basis (box plots) and enable comparison with nine TBMs (colored broken lines). The mean quantum yield at 25°C closely agreed with the mean TBM parameterization but at lower air temperatures, measured quantum yield diverged from TBMs. At 5°C quantum yield was markedly reduced and 60% lower than TBM estimates. The convexity factor also showed a significant reduction between 25°C and 5°C. At 5°C convexity was 38% lower than the common model parameterization. These data show that TBMs are not accounting for observed reductions in quantum yield and convexity that can occur at low temperature. Ignoring these reductions could lead to a marked overestimation of CO₂ assimilation at low light and low temperature.

Principal Investigator

Alistair Rogers
Brookhaven National Laboratory
[email protected]

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

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

Related Links

• NGEE–Arctic

References