Grazing mediates soil nutrient stocks through changing the plant functional composition and plant biomass allocation in alpine grassland

Abstract

Grazing can affect soil nutrient pools in a top-down process primarily through foraging, trampling and excreting of livestock. However, how grazing affects the relative contribution of plant biomass allocation to soil stoichiometry and nutrient storage in alpine grassland remains unclear. In this study, a 3-year serial grazing trail was conducted under 2 grazing regimes (continuous grazing and rotational grazing) and 3 grazing intensities (light grazing, medium grazing and heavy grazing) in an alpine steppe on Qinghai-Tibetan Plateau (QTP) to examine the effects of plant biomass allocation on soil stoichiometry and soil nutrient stock. The results showed that grazing decreased the aboveground biomass, whereas increased the belowground biomass and R:S. Grazing increased SOC stock and soil TP stock but did not affect the TN stock. Meanwhile, grazing caused an increasing in C: N and N: P. The shifts in belowground biomass and R: S regulates the changes of C: N: P stoichiometry. The plant functional composition regulated the changes of SOC stock, TN stock and TP stock. The relative contribution of R: S ratio to SOC stock and TN stock were increased with grazing intensities. We concluded that moderately rotational grazing is beneficial to better plant resource allocation and to regulate the soil nutrient stock in the alpine grassland ecosystem. These findings are crucial to identify the feasible grazing practices for the QTP’s alpine grasslands.