Improved Global Maps of the Optimum Growth Temperature, Maximum Light Use Efficiency, and Gross Primary Production for Vegetation

The optimum growth temperature (T-opt) and maximum light use efficiency (epsilon(max)) of terrestrial vegetation are closely related to plant photosynthesis in current and future Earth environments, yet little is known about their spatial distributions at the global scale. This study derived global maps of T-opt and epsilon(max) separately, under the light use efficiency (LUE) model framework by utilizing FLUXNET measurements and satellite-observed solar/sun-induced chlorophyll fluorescence (SIF), as well as multiple regression and neural network regression based on environmental and biological factors. T-opt is found to be positively correlated with annual mean temperature (T), except in cold areas with T < 9 degrees C, where T-opt stays within the range of 10 degrees C-15 degrees C. T-opt is equal to T in tropical areas with T >= 25 degrees C, but is obviously higher than T in other regions. epsilon(max) is high in regions with a large amount of diffuse radiation and increases significantly with water stress. The maps of T-opt and epsilon(max) improved the global gross primary production (GPP) estimation (R-2 = 0.83, RMSE = 1.38 g C m(-2) d(-1) against flux observations). The average annual GPP was 126 +/- 1.5 PgC yr(-1), with a trend of 0.6 +/- 0.1 PgC yr(-2) during 2001-2016, faster than most previous estimates. Our study suggests that the positive anthropogenic impacts on GPP were underestimated in existing products, including cropland expansion in southern Brazil and afforestation/forest protection efforts in China and western Europe. This study also provides a potential method for unified GPP modeling under the LUE framework.

Automated summary

This study derived global maps of the optimum growth temperature (T-opt) and maximum light use efficiency (epsilon(max)) of terrestrial vegetation using FLUXNET measurements and satellite-observed data. The study found that T-opt is positively correlated with annual mean temperature, while epsilon(max) is high in regions with a large amount of diffuse radiation and increases significantly with water stress. The maps improved global gross primary production estimation and highlighted the underestimated anthropogenic impacts on GPP in existing products.