Effects of nitrogen addition on rhizospheric soil microbial communities of poplar plantations at different ages

Abstract The continuous increase of nitrogen (N) deposition has had strong impacts on the structure and health of forest ecosystems globally. An elucidation of the shifts in rhizospheric microbial communities and their interactions with environmental factors under N-addition will assist us with better understanding the responses of forest ecosystems to future environmental changes. In this study, we employed high-throughput sequencing to investigate the responses of rhizosphere soil bacterial and fungal communities to seven-years of N-addition in young (9-year) and mature (14-year) poplar plantations in coastal Eastern China. The experiment included three N-addition levels: 0 (N0), 100 (N1), and 300 (N2) kg N ha−1 yr−1. The results revealed that soil fungal, but not bacterial, alpha-diversity significantly declined under the seven-year N-addition in mature poplars. Moreover, both bacterial and fungal community structures were significantly altered. The total C and NO3− contents controlled the patterns of soil bacteria community structures in mature poplar plantations, while soil pH, NO3−, total N, and C/N were the main factors that shaped the patterns of soil fungi communities in both poplar plantations. However, the relative abundance of plant pathogenic genera Mycoleptodiscus and Plectosphaerella increased strongly with N-addition. The soil microbial communities of mature poplar plantations were sensitive to N-addition. Our findings suggested that long-term simulated N deposition reduced fungal alpha-diversity, altered the composition of bacterial and fungal communities, while boosting the abundance of pathogenic communities, which may induce disease and otherwise damage forest ecosystems.