Estimating site-specific optimum air temperature and assessing its effect on the photosynthesis of grasslands in mid- to high-latitudes
Qing Chang, Xiangming Xiao, Xiaocui Wu, Russell Doughty, Wenzhe Jiao, Rajen Bajgain, Yuanwei Qin, Jie Wang
Abstract
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 ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">o</mml:mi> <mml:mi mathvariant="normal">p</mml:mi> <mml:mi mathvariant="normal">t</mml:mi> <mml:mo>−</mml:mo> <mml:mi mathvariant="normal">b</mml:mi> </mml:mrow> </mml:msub> </mml:math> ) parameter. To what degree will the site-specific optimum air temperature ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">o</mml:mi> <mml:mi mathvariant="normal">p</mml:mi> <mml:mi mathvariant="normal">t</mml:mi> <mml:mo>−</mml:mo> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> </mml:msub> </mml:math> ) affect GPP simulation results remains unclear. In this study, we estimated <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">o</mml:mi> <mml:mi mathvariant="normal">p</mml:mi> <mml:mi mathvariant="normal">t</mml:mi> <mml:mo>−</mml:mo> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> </mml:msub> </mml:math> by using GPP data from 11 grassland eddy flux tower sites (GPP EC ) and satellite vegetation indices (NDVI and EVI). We found that T opt-s parameter values estimated from EVI have good consistency with those from GPP EC 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">o</mml:mi> <mml:mi mathvariant="normal">p</mml:mi> <mml:mi mathvariant="normal">t</mml:mi> <mml:mo>−</mml:mo> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> </mml:msub> </mml:math> 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">o</mml:mi> <mml:mi mathvariant="normal">p</mml:mi> <mml:mi mathvariant="normal">t</mml:mi> <mml:mo>−</mml:mo> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> </mml:msub> </mml:math> in terrestrial GPP models, especially in those situations with large temperature variation (heatwave and cold spill events).