Grazing enhances plant photosynthetic capacity by altering soil nitrogen in alpine grasslands on the Qinghai-Tibetan plateau

Abstract The eco-physiological processes associated with the influences of grazing on plant traits and soil properties of alpine grasslands has remained poorly understood. To determine the effects of grazing on photosynthesis of alpine grassland plants, we measured nutrient level in plant and soil, as well as photosynthetic parameters of common herbage species in the grazed and fenced plots of an alpine meadow and an alpine steppe on Qinghai-Tibetan plateau. The results showed that grazing significantly enhanced most herbages’ carbon(C) and nitrogen (N) content, net photosynthetic rate ( A ), stomatal conductance ( gs ), intercellular CO 2 concentration ( Ci ), transpiration rate ( Tr ), water use efficiency ( WUE ) and light use efficiency ( LUE ), as well as soil C and N content. Through the SEM modeling, we found both direct and indirect paths that grazing enhanced plants photosynthetic capacity. Grazing can directly enhance soil N content and thus promote plant N uptake, further increase plant gs , WUE and LUE , finally promote the A of plants. Additionally, grazing can also directly enhanced plant photosynthetic capacity through promoting the plant gs . Soil N and plant gs are the two key factors that determine the improvement of photosynthetic capacity under grazing. Sustainable moderate grazing management is expected to promote the photosynthetic potentials of alpine plants mainly through the improvement of soil N.