Estimating site-specific optimum air temperature and assessing its effect on the photosynthesis of grasslands in mid- To high-latitudes

Abstract

The effect of air temperature on photosynthesis is important for the terrestrial carbon cycle. The optimum air temperature for photosynthesis is one of the major parameters in data-driven and process-based photosynthesis models that estimate the gross primary production (GPP) of vegetation under a changing climate. To date, most models use the biome-specific optimum air temperature (Topt-s) parameter. To what degree will the site-specific optimum air temperature (Topt-s) affect GPP simulation results remains unclear. In this study, we estimated Topt-s by using GPP data from 11 grassland eddy flux tower sites (GPPEC) and satellite vegetation indices (NDVI and EVI). We found that T opt-s parameter values estimated from EVI have good consistency with those from GPPEC at individual sites. We also evaluated the effects of site-specific and biome-specific optimum air temperature parameters on grassland photosynthesis. The results showed that the use of Topt-s in the Vegetation Photosynthesis Model improved to various degrees in both daily and annual GPP estimates in those grassland flux tower sites. Our results highlight the necessity and potential for the use of Topt-s in terrestrial GPP models, especially in those situations with large temperature variation (heatwave and cold spill events).