Terrestrial biosphere models may overestimate Arctic CO₂ assimilation if they do not account for decreased quantum yield and convexity at low temperature

• Published in: The New phytologist 2019-07, Vol.223 (1), p.167-179
• Main Authors: Rogers, Alistair, Serbin, Shawn P., Ely, Kim S., Wullschleger, Stan D.
• Format: Article
• Language: English
• Subjects: Absorptance; Absorptivity; Assimilation; Biological assimilation; Biosphere; Carbon cycle; Carbon dioxide; Carbon dioxide fixation; Carbon sequestration; Convexity; Critical components; curvature; ENVIRONMENTAL SCIENCES; Herbivores; high latitude; Irradiance; Leaves; light; Low temperature; Parameterization; Photosynthesis; plant; Plant species; Reflectance; Temperature effects; tundra; vegetation; Yields
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.15750

How terrestrial biosphere models (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. We measured the effect of temperature on the response of photosynthesis to irradiance in six Arctic plant species and determined the quantum yield of CO₂ fixation (ϕCO₂) and the convexity factor (θ). We also determined leaf absorptance (α) from measured reflectance to calculate ϕCO₂ on an absorbed light basis (ϕCO₂.a) and enabled comparison with nine TBMs. The mean ϕCO₂.a was 0.045 mol CO₂ mol−1 absorbed quanta at 25°C and closely agreed with the mean TBM parameterisation (0.044), but as temperature decreased measured ϕCO₂.a diverged from TBMs. At 5°C measured ϕCO₂.a was markedly reduced (0.025) and 60% lower than TBM estimates. The θ also showed a significant reduction between 25°C and 5°C. At 5°C θ was 38% lower than the common model parameterisation of 0.7. These data show that TBMs are not accounting for observed reductions in ϕCO₂.a and θ that can occur at low temperature. Ignoring these reductions in ϕCO₂.a and θ could lead to a marked (45%) overestimation of CO₂ assimilation at subsaturating irradiance and low temperature.