Objective   Effects of AMF and organic fertilizer on nitrogen (N) transformation and microbial N-cycling gene in rhizosphere soil at sweet corn field were studied to improve the fertilization practice.

  Method  In a field experiment, sweet corn was planted under various fertilization treatments, and the N-transformation between the plants and the soil monitored. The high-throughput sequencing platform, GeoChip 5.0, was used to determine the microbial community structure and N-cycling genes. Upon the base fertilization of P₂O₅ 150 kg·hm^-2 and K₂O 225 kg·hm^-2, 7 modifications were applied with 3 replicates for the soil treatments: (1) no N addition (CK), (2) optimized fertilization (OF), (3) organic N replacing 10% chemical N (ORF10), (4) organic N replacing 20% chemical N (ORF20), (5) ORF10 inoculated with Glomus versiforme (ORF10+AMF), (6) ORF20 inoculated with G. versiforme (ORF20+AMF), and, (7) CK inoculated with G. versiforme (CK+AMF). The physical and chemical analyses were performed on the plant and soil samples, and GeoChip 5.0 analyzed the community structure and N-cycling genes of the microbes in the rhizosphere soil under different treatments.

  Result  The inoculation of G. versiforme in soil significantly increased the N utilization efficiency by the sweet corn plants as well as the activity of N metabolizing enzymes in the rhizosphere microorganisms. When AMF inoculation combined with organic N fertilization, significant effects were observed on increases of the efficiency of N fertilizer (NAE), partial productivity of N fertilizer (PFP), and absorption and utilization efficiency of N fertilizer (NRE) between the plants and the soil, as well as the activities of nitrate reductase (NR), glutamic acid synthetase (GOGAT), and glutamine synthetase (GS) in the microbes. Among all treatments, ORF20+AMF improved the N utilization by the plants the greatest—NAE, PFP, NRE, and NPE rose by 31.15%, 28.08%, 6.95%, and 10.41%, respectively, over those under OF. The relative signal intensities of NiR, narB, nasA, nirA, nirB, napA, nrfA, nifH, and ureC in ORF10+AMF or ORF20+AMF were significantly higher than those in ORF10 or ORF20. That of hzo in ORF 20+AMF, in contrast, decreased by 20% compared with ORF20, which inviably caused a decreased N release by ways of N₂.

  Conclusion   The presence of AMF in soil enhanced the relative signal intensities of assimilating nitrogen reducing gene NiR, narB, nasA, nirA, and nirB, the N-reducing napA and nrfA , N-fixing nifH , ammonifying ureC, improved the NAE, PFP, and NRE, and increased the microbial N metabolizing enzyme activities. Meanwhile, the declined signal intensities on nitrifying hao, and ammoxidating hzo augmented the N-transformation from soil to plant. The application of AMF and organic fertilizer could, hence, be a promising approach to mitigate the dependency on chemical N fertilizer while promoting the crop yield of sweet corn in the field.