Impact of 36 years of nitrogen fertilization on microbial community composition and soil carbon cycling-related enzyme activities in rhizospheres and bulk soils in northeast China

peer reviewedNitrogen (N) deposition can change ecosystem functions but little is known of long-term N-deposition and rhizosphere effects on the microbial community composition and enzymes activities related to the carbon (C) cycle in the black soil common to northeastern China. Here, we studied two enzyme activities involved in C cycles and microbial community composition in both the rhizosphere and bulk soil from a long-term (36-year) fertilization field experiment. N-addition significantly decreased bacterial abundance and phenol oxidase activity, but enhanced fungal abundance and peroxidase activity, in both the rhizosphere and bulk soil. The fungal diversity exhibited more obvious shifts than the bacterial diversity after long-term N-addition, resulting in significantly decreased bacterial and fungal diversity levels, except for bacterial diversity in the rhizosphere, which was not significantly changed. Moreover, the enzyme activities and the bacterial and fungal abundance levels were higher in the rhizosphere than in the bulk soil, suggesting a rhizosphere effect on microbial activities involved in the C cycle. There was a significant difference in the microbial community compositions among different N-addition levels. A lesser β-diversity response to N-addition was observed in the rhizosphere than in the bulk soil, and the responses of fungal communities were greater than those of bacterial communities. Our findings suggested that rhizosphere effects and fertilization regimes both have significant influences on microbial communities and soil enzyme activities, and that fungi were more sensitive than bacteria in responding to N-deposition. © 201