Short-term yak-grazing alters plant-soil stoichiometric relations in an alpine meadow on the eastern Tibetan Plateau

Background and aims Over-grazing have significantly altered above- and belowground functions in terrestrial ecosystem. However, the influence of grazing intensity on plant-soil stoichiometric relations in alpine ecosystems remains unclear. Methods We investigated the responses of plant-soil nutrient stoichiometric relationships to four grazing intensities (un-grazing (UG), light grazing (LG), moderate grazing (MG) and heavy grazing (HG)) in an alpine meadow on the eastern Tibetan Plateau. We measured carbon (C), nitrogen (N), phosphorus (P) and potassium (K) concentrations and their ratios in plants and soils in the peak growing season after three years of yak-grazing. Results Compared to UG and LG plots, heavier grazing intensity at community levels and taxonomic groups decreased plant C and K concentrations by 7.6-10.5% and 17.6-21.3%, respectively, while grazing did not significantly influence plant N and P concentrations. Grazing intensity altered plant C:N and C:P ratios but not C:K and N:P ratios. By contrast, grazing intensity had no significant effects on soil nutrients and stoichiometry. Thus, the differential responses of plant and soil nutrients to grazing intensity caused that plants were more sensitive to grazing than soils. Conclusions Our results confirm that grazing intensity has differential effects on plant and soil nutrients, implying that plant nutrients do not covary with soil nutrients under changing grazing intensity and challenging the past positive relations between plant and soil nutrients. Further long-term grazing experiments are required to understand the drivers of grazing effect on plant-soil nutrient interactions.