Divergent responses of soil microbial community to long-term nitrogen and phosphorus additions in a subtropical Chinese fir plantation.

[Display omitted] • N addition decreases bacterial diversity by triggering soil acidification. • Soil bacterial community shifts from Acidobacteria to Actinobacteria under N addition. • The Resin-P, HCl- P and NaOH-Pi show positive relationship with the fungal Chao1. • Changes of soil bacterial and fungal communities are indicated by enzyme stoichiometry. • Soil microbial diversity is regulated by abiotic factor rather than microbial interaction. Nitrogen (N) and phosphorus (P) additions can alter the aboveground plant community structure, affecting ecosystem function. However, the mechanisms underlying belowground microbial community composition in response to N and P additions remain poorly understood in subtropical forests. We conducted a nine-year nutrient manipulation experiment in a Chinese fir plantation. We collected soil samples from three soil layers (0–5 cm, 5–10 cm, and 10–20 cm) and measured P fractions, microbial enzyme activity, microbial community, and other physicochemical properties. We found that N addition significantly decreased bacterial Chao1 and Shannon index at a 0–10 cm soil layer, while P addition increased fungal Chao1 at a 0–5 cm soil layer. Furthermore, N addition changed the bacterial composition structure, decreasing the relative abundance of Acidobacteria , while increasing that of Actinobacteria. N and P additions did not change interactions between microbial species and network complexity. N and P additions increased the soil enzyme stoichiometry ratios of BG: NAG and BG: AP at three soil layers. N addition exacerbated soil acidification with increased NH 4 +-N and NO 3 −-N, and decreased soil pH, which caused the decline of bacterial diversity. Resin-P, NaOH-P, HCl-P, and BG: AP ratio were positively correlated with fungal diversity. Moreover, the BG: NAG ratio was related to the relative abundance of dominant bacterial phyla (Acidobacteria and Actinobacteria). Our results suggested that nutrient addition affected soil bacterial and fungal communities via alteration of pH and P fractions rather than microbial interactions, which was confirmed by the enzyme stoichiometry response. These findings highlight how the soil microbial community may respond to future scenarios of anthropogenic N and P deposition in subtropical forests. [ABSTRACT FROM AUTHOR]