Nitrogen transformation and microbial community structure varied in apple rhizosphere and rhizoplane soils under biochar amendment

Biochar amendment is commonly applied to ameliorate soil environment and alleviate nitrous oxide (N2O) emissions, while our understanding of biochar effects on microbial community and nitrogen transformation traits of orchard root region soil is limited. We observed the composition and diversity of bacterial, fungal, and archaeal communities in apple root region (non-rhizosphere, rhizosphere, and rhizoplane) soils amended with apple wood biochar using the Illumina sequencing methods. We used quantitative PCR to quantify the abundance of nitrogen-transforming functional marker genes involved in microbial nitrogen fixation (nifH), nitrification (archaeal amoA and bacterial amoA), and denitrification (nirK, nirS, and nosZ). Biochar amendment altered bacterial, fungal, and archaeal community compositions in apple root region soil. When compared to control, biochar additions dramatically increased the α-diversity of bacteria in the rhizoplane soil, whereas amendment significantly decreased the α-diversity of fungi and archaea in the rhizosphere soil. Moreover, the driving factors varied in non-rhizosphere, rhizosphere, and rhizoplane soils. The abundance of nitrogen-fixing microorganisms and microbial N2O reduction were enhanced by biochar amendment in rhizosphere and rhizoplane soils, which was associated with an observed reduction in N2O concentrations by 13.7 and 35.1% in the 15- and 20-cm soil layer. However, wood biochar amendment had insignificant effect on nifH and amoA gene abundances in non-rhizosphere soil. Network analysis revealed that nitrogen-transforming functional genes had an intensive potential link to multiple microbial phyla. The soil microbial community was altered in biochar-amended soil by changing soil properties, thereby regulating nitrogen transformation processes and N2O concentrations in apple root region soil.