Potassium mediates succession of microbial community and nitrogen functions under long-term sloping cultivation with soybean

Abstract

Sloping farmland significantly increases soil erosion and the loss of nutrients and organic carbon. However, there is limited knowledge about the potential impacts of changes in soil physicochemical properties on the microbial community and its metabolic functions. Here, we investigated the responses of bacterial diversity, complexity, stability, and metabolic functions during sloping soybean cultivation over periods of 6, 6.5, and 8 years. The results indicated that long-term sloping cultivation markedly reduced the diversity of the bacterial community but noticeably increased its richness. Co-occurrence network’s links, degree, and robustness were diminished, while vulnerability increased after long-term sloping cultivation, indicating a reduction in the complexity and stability of bacterial community in sloping farmland. However, the overlapping nodes, compositional stability, and node persistence were significantly higher in sloping farmland than those in normal farmland. This result suggested that sloping cultivation selected specific core microorganisms that exhibited minimal changes over time. Those core microbes showed significantly higher metabolic functions related to the dissimilatory and assimilatory reduction of nitrate to ammonium in sloping farmland. Compared with the CK, the sloping farmland significantly increased available potassium by 37.9 %. In sloping farmland, higher available potassium was a driving factor in increasing microbial richness and enhancing compositional stability and node persistence, which further improved the potential functions of nitrate reduction to ammonium. Generally, changes in soil properties, especially the increase in available potassium, contributed to the selection of specific core microbes with a high capacity for nitrate utilization. Our findings suggested that the future utilization of sloping farmlands should consider their impacts on microbial functions, especially nitrogen metabolism.