AUTHOR=Ren Ning , Wang Yang , Ye Youliang , Zhao Yanan , Huang Yufang , Fu Wen , Chu Xv 

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

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.01948

DOI=10.3389/fmicb.2020.01948

ISSN=1664-302X

ABSTRACT=<p>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<sup>–2</sup>). 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<sup>–2</sup>. 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, <italic>Actinobacteria, Acidobacteria, Chloroflexi, Bacteroidetes, Gemmatimonadetes, and Patescibacteria</italic>. Among these, <italic>Proteobacteria</italic> and <italic>Gemmatimonadetes</italic> were found to be unaffected by the nitrogen fertilizer and soil environmental factors (pH, C/N ratio, and NO<sub>3</sub><sup>–</sup> concentration), whereas <italic>Acidobacteria</italic> and <italic>Actinobacteria</italic> showed significant positive and negative correlations, respectively, with soil pH. The richness of <italic>Actinobacteria</italic> significantly increased in the N<sub>180</sub> treatment. <italic>Patescibacteria</italic> and <italic>Bacteroidetes</italic> showed significant positive correlations with soil NO<sub>3</sub><sup>–</sup> and wheat yield, and the average relative richness of these two phyla was high under long-term application of the N<sub>180</sub> treatment. These findings indicate that the relative richness of <italic>Patescibacteria</italic> and <italic>Bacteroidetes</italic> 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 <italic>via</italic> changing the soil pH. The richness of <italic>Actinobacteria</italic> can serve as an indicator of a decreased soil pH caused by long-term N fertilization.</p>