Total phosphorus mediates soil nitrogen cycling in alpine meadows

PurposeThe overall nitrogen (N) cycling potential integrating multiple processes has not been examined, and the relative contributions of biotic and abiotic factors remain elusive. In this study, we proposed the N cycling index (NCI), based on the potential of biological N fixation, N mineralization, nitrification, and denitrification, as a comprehensive indicator to characterize the overall soil N cycling potential in alpine meadow.Materials and methodsThe potential of individual N process sampled from the alpine meadow of Qinghai-Tibetan Plateau was quantified using incubation experiments in the laboratory. Four individual N process potentials (biological N fixation, N mineralization, nitrification, and denitrification) were quantified and used to construct the NCI. The relative contributions of biotic (e.g., N-related microbial gene abundances, microbial community) and abiotic (e.g., geo-climate, soil, and plant properties) drivers shaping NCI were investigated using variation partitioning analysis and partial mantel test. The mechanism of the key factors controlling the overall soil N cycling potential in alpine meadow was revealed using structural equation modeling (SEM).Results and discussionThe soil NCI varied sensitively with the potential of individual N process, and it showed the highest and positive correlations with the denitrification potential in alpine meadows. Soil properties, N-related microbial gene abundances, alpha-diversity of bacterial and fungal communities, and fungal beta-diversity showed significant and positive relationships with soil NCI. Soil total phosphorous (TP) showed the greatest influence on NCI among all the environmental factors. Soil TP remarkably mediated NCI directly and indirectly by affecting N-related gene abundances.ConclusionsThe NCI could be used to indicate overall soil N cycling potentials and soil TP played a critical role in mediating soil N cycling in alpine meadow. Together, these findings provided novel insights into the important prediction of TP in the overall soil N cycling potential in alpine ecosystem.