Effects of novel nitrogen fertilizers application on the community composition of nitrogen-fixing microorganisms in maize rhizosphere soils
In order to explore the effects of novel nitrogen fertilizers application on the community composition of soil nitrogen-fixing microorganisms,soil samples from long-term maize continuous cropping systems were collected from the rhizosphere of mature maize throughout a long-term localization experiment(starting in 2014).The differences in nitrogen-fixing microbial nifH gene-expressing communities were evaluated in three groups treated with three novel nitrogen fertilizers:controlled-release urea(SU),stable fertilizer(SF),and sulfur-coated urea(SCU);these treatment strategies were compared with conventional urea(CU)and analyzed using no nitrogen fertilizer(N0)as a control.The results demonstrated that the abundance of nifH gene-expressing in the N0 treatment group was higher than that in the treatment groups with nitrogen fertilizers.Overall,nifH gene abundance was significantly lower in the SF treatment group(3.4×106 copies·g-1)than that in the other groups.The pH(relative influence:44.51%)and organic matter(relative influence:35.01%)were the main factors that affected nifH gene abundance.Nitrogen fertilization reduced the richness and diversity of nitrogen-fixing nifH-expressing microorganisms compared to those observed in the N0 treatment group;additionally,the novel nitrogen fertilizers increased the richness index but decreased the diversity index compared to the CU treatment.The dominant nitrogen-fixing nifH-expressing microbial genera were determined to be Desulfovibrio(relative abundance:14.11%-33.39%),Stenotrophomonas(relative abundance:2.66%-17.72%),and Bradyrhizobium(relative abundance:2.68%-6.32%).Nitrogen fertilizer application had a significant impact on the community structure(P=0.001);however,the impact of novel nitrogen fertilizer treatments on community structure was not significantly different to that of conventional urea treatment(P=0.1).The effect of novel nitrogen fertilizer types on nifH gene diversity was higher than that of traditional nitrogen application;however,fewer changes in nifH gene structure were observed in the novel nitrogen fertilizer groups than that in the traditional nitrogen application group.Our results indicate that the application of novel nitrogen fertilizers increases the nifH gene pool in nitrogen-fixing microorganisms,alters community structure,and provides a new theoretical direction for the use of novel nitrogen fertilizers in agricultural ecosystems.
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