In this study,we investigated the potential nitrification and community structure of soil-based a mmonia-oxidizing bacteria(AOB)in apple orchard soil during different growth periods and explored the effects of environmental factors on nitrification activity and AOB community composition in the soil of a Hanfu apple orchard,using a culture-dependent technique and denaturing gradient gel electrophoresis(DGGE).We observed that nitrification activity and AOB abundance were the highest in November,lower in May,and the lowest in July.The results of statistical analysis indicated that total nitrogen(N)content,NH4+-N content,NO3--N content,and pH showed significant correlations with AOB abundance and nitrification activity in soil.The Shannon-Winner diversity,as well as species richness and evenness indices(determined by PCR-DGGE banding patterns)in soil samples were the highest in September,but the lowest in July,when compared to additional sampled dates.The DGGE fingerprints of soil-based 16S rRNA genes in November were apparently distinct from those observed in May,July,and September,possessing the lowest species richness indices and the highest dominance indices among all four growth periods.Fourteen DGGE bands were excised for sequencing.The resulting analysis indicated that all AOB communities belonged to theβ-Proteobacteria phylum,with the dominant AOB showing high similarity to the Nitrosospira genus.Therefore,soil-based environmental factors,such as pH variation and content of NH4+-N and NO3--N,can substantially infl uence the abundance of AOB communities in soil,and play a critical role in soil-based nitrification kinetics. In this study, we investigated the potential nitrification and community structure of soil-based a mmonia-oxidizing bacteria (AOB) in apple orchard soil during different growth periods and explored the effects of environmental factors on nitrification activity and AOB community composition in the soil of a Hanfu apple orchard, using a culture-dependent technique and denaturing gradient gel electrophoresis (DGGE) .We observed that nitrification activity and AOB abundance were the highest in November, lower in May, and the lowest in July. The results of statistical analysis showed that total nitrogen (N) content, NH4 + -N content, NO3 - N content, and pH showed showed correlations with AOB abundance and nitrification activity in soil. Shannon-Winner diversity, as well as species richness and evenness indices (determined by PCR-DGGE banding patterns) in soil samples were the highest in September, but the lowest in July, when compared to additional sampled dates. DGGE fingerprints of soil-based 16 S rRNA genes in November were apparently distinct from those observed in May, July, and September, possessing the lowest species richness indices and the highest dominance indices among all four growth periods. Courteen DGGE bands were excised for sequencing. The results analysis indicated that all AOB communities belonged to the β-Proteobacteria phylum, with the dominant AOB showing high similarity to the Nitrosospira genus. Herefore, soil-based environmental factors, such as pH variation and content of NH4 + -N and NO3- N, can substantially infl uence the abundance of AOB communities in soil, and play a critical role in soil-based nitrification kinetics.