Effects of Continuous Nitrogen Fertilizer Application on the Diversity and Composition of Rhizosphere Soil Bacteria.

Little has been reported on the effects of long-term fertilization on rhizosphere soil microbial diversity. Here, we investigated the effects of long-term continuous nitrogen (N) fertilization on the diversity and composition of soil bacteria using data from a 10-year field experiment with five N application rates (0, 120, 180, 240, and 360 kg N hm). The results revealed varying degrees of reduction in the numbers of bacterial operational taxonomic units (OTUs) in response to the different N application rates. The highest wheat yield and number of proprietary bacterial OTUs were found in the N input of 180 kg N hm. In terms of average relative richness, the top seven phyla of soil bacteria in the rhizosphere of wheat after long-term nitrogen application were Proteobacteria, . Among these, and were found to be unaffected by the nitrogen fertilizer and soil environmental factors (pH, C/N ratio, and NO concentration), whereas and showed significant positive and negative correlations, respectively, with soil pH. The richness of significantly increased in the N treatment. and showed significant positive correlations with soil NO and wheat yield, and the average relative richness of these two phyla was high under long-term application of the N treatment. These findings indicate that the relative richness of and can affect wheat yield. In conclusion, the results of our 10-year field experiments clearly show that long-term N fertilization can significantly affect most of the dominant soil bacterial species changing the soil pH. The richness of can serve as an indicator of a decreased soil pH caused by long-term N fertilization.