Responses of Different Soil Microbial Communities to the Addition of Nitrogen into the Soil of Larix gmelinii var. principis-rupprechtii (Mayr) Pilg. Plantations

The increasing rate of atmospheric nitrogen (N) deposition caused by human activities is a global concern. A rise in N deposition can alter the soil microbial community, as demonstrated by most long-term N addition experiments. Nevertheless, it remains unknown how short-term N addition influences the early succession of the soil microbial community in forests. In this study, the responses of the soil microbial community to multi-level and short-term (one-year) N addition in the soil of Larix gmelinii var. principis-rupprechtii (Mayr) Pilg. plantations in the Yanshan Mountains were explored. We used high-throughput sequencing technology to analyze the 16S rRNA of bacteria, the ITS gene of fungi, and the nifH functional gene of N-fixing bacteria. The results revealed a decrease in N-fixing functional gene abundance (such as nifH) and a slight rise in fungal and bacterial copy number due to N addition. N addition influenced the N-fixing bacterial community but had no influence on the fungal and bacterial communities in general. It drastically decreased the diversity of N-fixing microbial communities while having little impact on the diversity of fungi and bacteria. The NO3−-N concentration exhibited a negative connection with the Shannon–Wiener index of the N-fixing microbial community when it exceeded a specific limit. Actinomycetes and N-fixing bacteria were significantly negatively correlated. The changes in soil NO3−-N concentration and abundance of actinomycetes were the main reasons for the decrease in N-fixing microbial community diversity. The results of this study set the groundwork for exploring the initial succession mechanisms of soil microorganisms after N addition. This study offers a scientific theoretical basis for precise management of plantations under N deposition.