Optimal temperature for grassland vegetation productivity

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Anping Chen, Department of Biology, Colorado State University, Fort Collins, CO and Qiang Liu, University of Antwerp

Background/Question/Methods
The rate of plant photosynthetic carbon sequestration is temperature sensitive, predominately showing a unimodal curve that first increases then decreases with temperature. Temperature corresponding to the maximum productivity is called optimal temperature, which is a key parameter for modelling photosynthesis responses. With climate change, there is a pressing need to know if future warming will surpass the optimal temperature for vegetation productivity (Topt), and thus shift to reduce photosynthesis and productivity. Much of our knowledge on Topt, however, is derived from plant autecological studies, which do not directly translate into information that can be used for the modelling and prediction of photosynthetic production at regional or global level. Here, we used satellite derived near-infrared reflectance of vegetation (NIRv) data to map optimal temperature of vegetation productivity (Topt) at the spatial resolution of 0.1 degree for grasslands in the Tibetan Plateau (TP), Mongolian Plateau (MP), and the North American Great Plains (GP).
Results/Conclusions
We observed a remarkable geographical heterogeneity in Topt across these grasslands. Importantly, the average Topt is significantly lower than the Topt value used in current ecosystem models. Topt increases by 0.66 oC for each 1 oC of rising mean annual temperature as a result of vegetation adaptation to climate change. Topt also tends to decrease by 0.41 oC per 100 m increase in elevation, faster than the elevational elapse rate of growing season temperature, implying a potential CO2 regulation of Topt in addition to temperature acclimation. Our analyses imply that the temperature tipping point when the impact of future warming shifts from positive to negative for grasslands is strongly overestimated by current vegetation models. Future research needs to include varying thermal and CO2 acclimation effects on Topt across different time scales in vegetation models.