Abstract: We conducted an 11-year nitrogen (N) addition experiment (control: 0 kg·hm^-2·a^-1, low N addition: 80 kg·hm^-2·a^-1, high N addition: 150 kg·hm^-2·a^-1) in Larix principis-rupprechtii plantations in Guandi Mountain, Lvliang City, Shanxi Province, to analyze the impact of long-term N input on soil microbial community structure and diversity by using high-throughput sequencing technology, redundancy analysis (RDA) and Mantel test. The results showed that both low and high N additions significantly increased soil nitrate (NO₃^--N) content, total nitrogen (TN) content, and microbial quotient for carbon, while significantly reduced soil pH and total phosphorus (TP) content. High N addition markedly decreased α-diversity indices (ACE, Chao1, Shannon, and Simpson) of both bacteria and fungi. Proteobacteria was the dominant bacterial phylum, accounting for 31.6%-46.5% of the total bacterial sequences, followed by Acidobacteria (20.8%-26.2%) and Bacteroidetes (6.8%-8.9%). The fungal community was dominated by Basidiomycota (31.6%-46.5%), Ascomycota (24.5%-39.7%), Mortierellomycota (3.1%-5.1%), and Rozellomycota (2.3%-3.2%). Nitrogen addition significantly reshaped community composition of bacteria and fungi. For bacteria, low N addition significantly increased the relative abundances of Acidobacteria, Acidobacteriaceae Gp4, and Nitrospira, decreased those of Proteobacteria and Acidobacteriaceae Gp17. For fungi, both low and high N additions significantly reduced the relative abundance of Suillus, while high N addition further decreased the relative abundance of Ascomycota and Glomeromycota. RDA and Mantel test demonstrated that the key environmental factors affecting bacterial communities were soil TP, avai-lable phosphorus (AP), and C/N, whereas those affecting fungal communities were soil AP, soil organic carbon (SOC), and pH. Bacterial diversity indices exhibited significant correlations with SOC, microbial biomass carbon (MBC), and pH, while fungal diversity indices were significantly correlated with TN, SOC, MBC, and C/N. In summary, low N addition improved soil fungal community structure and enhanced α-diversity by mitigating N limitation and optimizing soil C/N. In contrast, high N addition caused soil acidification and a reduction in SOC content, exhibited significant inhibitory effects on both bacterial and fungal communities.

Key words: nitrogen addition, Larix principis-rupprechtii, soil microbial community, high-throughput sequencing