Spring Rest-Grazing Time Influenced Soil Phosphorus Fractions by Altering the Abundance of Genes Involved in Phosphorus Cycling in a Subalpine Meadow.

Soil phosphorus (P) availability is a critical factor limiting plant growth and ecosystem productivity that can be strongly influenced by land use factors, such as grazing by livestock. Seasonal grazing management can benefit grassland productivity and soil nutrient cycling in alpine meadows, but its effects on soil P availability and the microbial processes driving P transformation remain poorly understood. To address this, a long-term field experiment was conducted with five different spring rest-grazing periods, where soil P fractions were examined and metagenomic sequencing was employed to assess the functional profiles of microbial genes involved in P cycling. Early spring rest-grazing led to higher concentrations of labile P fractions (Resin-P and NaHCO3-Pi), indicating improved soil P availability. Moreover, rest-grazing in early spring significantly reduced HCl-Pi concentration while increased the concentration of conc. HCl-Po. Metagenomic analysis revealed that early spring rest-grazing may have contributed to a higher relative abundance of the organic P mineralization gene phnA but decreasing the relative abundance of inorganic P solubilization genes ppa, and P-uptake and transport gene pstB. The dominant microbial genera involved in P cycling were Rhodopseudomonas and Mesorhizobium. Soil temperature and water infiltration rate, both affected by early rest-grazing, were identified as the main environmental variables correlated with P-cycling functional gene composition. These influenced taxa with functional genes involving organic P mineralization, inorganic P solubilization, and P-uptake and transport, which may associate with enhancing soil labile P. This study provides insights into potential microbial processes under grazing management in grassland ecosystems.