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(-2)). 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(-2). 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,Actinobacteria, Acidobacteria, Chloroflexi, Bacteroidetes, Gemmatimonadetes, and Patescibacteria. Among these,ProteobacteriaandGemmatimonadeteswere found to be unaffected by the nitrogen fertilizer and soil environmental factors (pH, C/N ratio, and NO(3)(-)concentration), whereasAcidobacteriaandActinobacteriashowed significant positive and negative correlations, respectively, with soil pH. The richness ofActinobacteriasignificantly increased in the N(180)treatment.PatescibacteriaandBacteroidetesshowed significant positive correlations with soil NO(3)(-)and wheat yield, and the average relative richness of these two phyla was high under long-term application of the N(180)treatment. These findings indicate that the relative richness ofPatescibacteriaandBacteroidetescan 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 speciesviachanging the soil pH. The richness ofActinobacteriacan serve as an indicator of a decreased soil pH caused by long-term N fertilization.