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

Abstract Nitrogen (N) deposition can change ecosystem functions but little is known of long-term N-deposition and rhizosphereeffects on the microbial community composition and enzymes activitiesrelated to the carbon (C) cycle in the black soil common to northeastern China. Here, we studied two enzyme activitiesinvolved in C cycles and microbial community composition in both the rhizosphereand bulk soilfrom 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 rhizosphereand bulk soil. The fungal diversityexhibited more obvious shifts than the bacterial diversity after long-term N-addition, resulting in significantly decreased bacterial and fungal diversitylevels, except for bacterial diversity in the rhizosphere, which was not significantly changed. Moreover, the enzyme activitiesand the bacterial and fungal abundance levels were higher in the rhizospherethan in the bulk soil, suggesting a rhizosphereeffect 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 rhizospherethan in the bulk soil, and the responses of fungal communities were greater than those of bacterial communities. Our findings suggested that rhizosphereeffects 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.