Grassland management regimes regulate soil phosphorus fractions and conversion between phosphorus pools in semiarid steppe ecosystems

Although livestock grazing can strongly affect pools and cycles of phosphorus (P) in grassland ecosystems, few studies have examined how grassland management regimes influence the components of the soil P pool. Here, we use a long-term experiment in the Inner Mongolia grassland to examine how grassland management and biotic and abiotic factors affect soil P fractions. The grassland management regimes we studied included a traditional grazing system (continuous grazing, TS), a mixed grazing system (grazing and mowing rotation, MS), and a haymaking system (continuous mowing, HS). Our results showed that traditional grazing accelerated the return of P to ecosystems lost by herbivores and decoupled labile P (i.e., Ca-2-P) from soil organic carbon in the topsoil (0-10 cm). Labile P was significantly reduced in the topsoil in HS (- 10%) and MS (- 24%). Mowing promoted the downward movement of soil P and the transformation of O-P to Ca-2-P in the topsoil by removing large amounts of biomass and litter. Both grazing and mowing increased Fe-P and Ca-10-P concentrations. The amount of labile P in the topsoil was mainly explained by plant properties, whereas the amounts of moderately labile P (Ca-8-P, Al-P and Fe-P) and stable P (O-P and Ca-10-P) were mainly explained by soil properties. Moreover, shifts in plant community composition resulted in substantial impacts on the soil stable P fractions. Our study demonstrates that long-term continuous grazing is detrimental to the accumulation of available nutrients in soils. Understanding how grazing and mowing affect conversion between P pools could improve adaptive grassland management in the face of global change.