Spatial patterns of light response parameters and their regulation on gross primary productivity in China

Light response parameters are used to model the photosynthetic processes of ecosystems, but they are usually considered as fixed or empirical values for specific vegetation type and their geographical variation and influence mechanisms at ecosystem scale remain unclear. In this study, we analyzed the light response parameters (photosynthetic quantum yields, alpha; maximum gross photosynthetic rate, Amax) at 64 typical ecosystems of ChinaFLUX over 20 years' measurement, to explore their spatial patterns and controlling factors. The results showed that the light response parameters significantly varied with ecosystem types: in grassland and desert ecosystems, both alpha and Amax were significantly lower than other ecosystems, and in cropland ecosystems, the Amax was significantly higher than that of other ecosystems. The light response parameters significantly decreased with increasing altitude. Vegetation index and photosynthetically active radiation were the dominant factor for the spatial variation of alpha, while the spatial variation of Amax was mainly controlled by moisture conditions. Compared to Amax, alpha was more stable which varied less with hydrothermal conditions. The dominant factors of light response parameters also differed among ecosystem types. Hydrothermal conditions regulated vegetation indexes and further modulate light response parameters and GPP. This study suggested that the quantitative analysis and simulation prediction of photosynthesis should consider the spatial heterogeneity of light response parameters and their different environmental responses at ecosystem scale in future studies.