Free-living Bacterial Community, Abundance and Edaphic Factors Response to Soil Depth Gradient under Contrasting Fertilization in Sugarcane Continuous Cropping Field

Abstract Although the effects of fertilization on soil N-fixing bacterial community and abundance have been investigated extensively in the surface soil (0–20 cm), the response of free-living bacterial community and abundance under contrasting fertilizations in a consecutive sugarcane monoculture field and their relationship with edaphic factors in the dipper (20–60 cm) soil layer remain elusive. In the current study, nifH gene amplicon sequencing was used to investigate N2-fixers bacterial community and abundance by leveraging high-throughput sequencing (HTS). Moreover, edaphic factors in three soil depths (0–20, 20–40 and 40–60 cm) under control (CK), organic matter (OM), biochar (BC) and filter mud (FM) amended soils were investigated. Our analysis revealed that β-glucosidase and phosphatase activities, and ammonium (NH4+-N), nitrate (NO3−-N), total carbon (TC), total nitrogen (TN) and available potassium (AK) were considerably higher in 0–20 cm in all treatments. Proteobacteria and Geobacter were dominant in all the samples, while 0–20 cm was overwhelmingly occupied by Anabaena, Enterobacter and Desulfovibrio in BC and FM amended soils, followed by Methylomonas in 20–40 cm under BC treatment. We also noticed that soil depth was the main environmental gradient that influenced soil diazotrophs and edaphic factors rather than fertilization. Together, these results suggest that soil depth had a profound impact on N-fixing bacteria, edaphic factors than fertilization regimes. Moreover, these findings were more pronounced in 0–20 cm soil depth under organic amendments compared with CK.