Variations of soil bacterial community and denitrifier abundance with depth under different land-use types

Purpose Long-term excessive application of nitrogen fertilizer under diverse land uses has caused serious environmental problems on the North China Plain. Current studies focus on denitrifiers and bacterial communities in topsoil under diverse land-use types; however, few studies have studied denitrifiers and microbial communities in subsoils. Materials and methods The variations in soil bacterial communities and denitrifiers with soil profiles (0-300 cm) under crop, apple orchard, and vegetable fields were investigated through high-throughput sequencing and quantitative PCR technologies. Results and discussion NO3--N largely accumulated in the deeper soil layers (100-300 cm) in the apple orchard, resulting in a higher risk of NO3--N leaching. The soil bacterial community structure at the 0-100 cm soil depth had a marketable difference from that at 100-300 cm under these three land-use types, and the C:N ratio was the main driving factor for their vertical distribution. The bacterial alpha-diversity decreased with soil depth; the crop field had the highest a-diversity across all horizons except 100-200 cm, and total carbon was the most important factor driving a-diversity. In addition, the absolute abundance of the nirK, nirS, and nosZ genes decreased with soil depth and varied with land-use type, which was deeply affected by multiple soil properties, such as soil organic matter and total nitrogen. Conclusion Our findings highlighted that potentially important and unique functions remain to be revealed in subsoils, which may provide new insights into mitigating nitrate leaching in various land-use types.