[Effects of nitrogen and water addition on soil bacterial diversity and community structure in temperate grasslands in northern China].

In this study, we measured the responses of soil bacterial diversity and community structure to nitrogen (N) and water addition in the typical temperate grassland in northern China. Results showed that N addition significantly reduced microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) under regular precipitation treatment. Similar declined trends of MBC and MBN caused by N addition were also found under increased precipitation condition. Nevertheless, water addition alleviated the inhibition by N addition. N addition exerted no significant effects. on bacterial α-diversity indices, including richness, Shannon diversity and evenness index under regular precipitation condition. Precipitation increment tended to increase bacterial α-diversity, and the diversity indices of each N gradient under regular precipitation were much lower than that of the corresponding N addition rate under increased precipitation. Correlation analysis showed that soil moisture, nitrate (NO3(-)-N) and ammonium (NH4+-N) were significantly negatively correlated with bacterial evenness index, and MBC and MBN had a significant positive correlation with bacterial richness and evenness. Non-metric multidimensional scaling (NMDS) ordination illustrated that the bacterial communities were significantly separated by N addition rates, under both water ambient and water addition treatments. Redundancy analysis (RDA) revealed that soil MBC, MBN, pH and NH4+-N were the key environmental factors for shaping bacterial communities.