Long-term sloping cultivation reduced core microbiota related to nitrogen fixation and soil hydrocarbon degradation

Sloping farmland increases soil erosion, but little is known about how soil erosion impacts microbial structures and functions in sloping farmland. Using high-throughput sequencing, we conducted a six-year in-situ experiment with gradients of 0° (CK), 5° (S1), 10° (S2), and 15° (S3) to investigate the effects of sloping farmland on soil microbial diversities, compositions, and functions related to nitrogen and carbon resource acquisition. The results showed that the S1, S2, and S3 treatments significantly decreased SOM and NO₃^- levels by 33.0%∼47.3% and 37.0%∼49.6%, respectively, in comparison to the CK treatment. The S1, S2, and S3 treatments had similar impacts on diversities and compositions of bacterial and fungal communities. Moreover, the S1, S2, and S3 treatments had same enriched and depleted core microbiota. Long-term sloping cultivation filtered these core microbiota mainly by reducing SOM and NO₃^- and increasing AK and AP. Compared with the CK treatment, the S1, S2, and S3 treatments significantly reduced the relative abundances of potential functions of nitrogen fixation, hydrocarbon degradation, and fermentation by 46.9%∼54.5%, 74.7%∼83.5%, and 28.1%∼54.1%, respectively. Sloping treatments reduced functions related to nitrogen fixation and soil hydrocarbon degradation mainly because the loss of SOM reduced the relative abundances of core microbiota. Generally, long-term sloping cultivation reduced core microbiota related to nitrogen fixation and soil hydrocarbon degradation mainly due to the loss of SOM. Our findings provided implications for the management and reclamation of sloping farmland.