Driving mechanisms of climate-plant-soil patterns on the structure and function of different grasslands along environmental gradients in Tibetan and Inner Mongolian Plateaus in China

Grassland plants contribute to carbon fixation through photosynthesis, which can in turn produce plant biomass. Previous studies have demonstrated that vegetation productivity is enhanced by improved soil nutrient status in humid environments and is influenced by climate in arid environments. However, the responses of biomass productivity to different patterns of climate-plant-soil in different natural grassland ecosystems have not been clearly and comprehensively analyzed. In this study, we systematically explore the functional patterns of different grasslands, as well as the underlying mechanisms in the response to key climatic, soil, and plant factors. The survey range covered broad environmental gradients from humid, semi-arid, to arid environments in Tibetan and Inner Mongolian Plateaus. We found that the above- and belowground biomass production gradually decreased from humid, semi-arid, to arid environments. Biomass production was sensitive to climatic factors in different environments. However, compared to soil and plant factors, climate was always the most important factor determining biomass production in all grassland types. Furthermore, biomass production was regulated mainly by climate and soil characteristics in humid environments, but by climate in arid environments. Specifically, the corresponding limiting factors of each factor largely dominated the effects of the corresponding factors on different grasslands. For instance, the climate dominated by temperature negatively influenced the soil nutrient availability and then influenced the aboveground biomass production in alpine humid grasslands. These findings enhance our understanding of the heterogeneity of mechanisms of different grasslands along broad environmental gradients, which are crucial for predicting the effects and consequences of environmental change on terrestrial ecosystem functioning.