Long-term application of nitrogen, not phosphate or potassium, significantly alters the diazotrophic community compositions and structures in a Mollisol in northeast China

Abstract This study investigated the effects of 35 years of application of inorganic fertilizerscontaining nitrogen (N), phosphate (P), or potassium (K) alone or in combination on the abundance and composition of diazotrophiccommunity in a black soil ( Mollisol) in northeast China. The abundance and composition of diazotrophiccommunity were analyzed using qPCR and Illumina MiSeq sequencing targeting nifH genes. Nitrogen fertilizationdecreased the abundance and Shannon diversity of nifH genes. The diazotrophiccommunity was dominated by Alphaproteobacteria( Bradyrhizobiumat the genus level), with relatively higher abundance in the N fertilizationtreatments than in the non-N fertilizationtreatments. All diazotrophiccommunities were clustered into two groups with and without N fertilizationhistory, and the soil pH, total C, total N, and NO 3 − -N significantly influenced the structure of the whole diazotrophiccommunity. Moreover, random matrixtheory analysis elucidated a clear difference in network structures between the N and non-N fertilizationtreatments, with N fertilizationcausing a less stable network structure. These results highlighted that it was N fertilizer, but not P and K fertilizers, contributed to great changes in the diazotrophiccommunity in this black agricultural soil.