Manure combined with biochar reduces rhizosphere nitrification potential and amoA gene abundance of ammonia-oxidizing microorganisms in acid purple soil

Fertilization and soil environmental factors determine the niche differentiation of ammonia-oxidizing microorganisms, thereby affecting the ammonia-oxidation process. However, the characteristics of rhizosphere potential nitrification rate (PNR), ammonia-oxidizing archaea (AOA), and ammonia-oxidizing bacteria (AOB) population under manure combined biochar are unclear. In this study, a pot experiment growing lemon was conducted, setting up six treatments, namely no fertilization (CK), chemical fertilizer (CF), manure (M), chemical fertilizer combined with biochar (CFBC), manure combined with biochar (MBC), fresh manure combined with biochar (FMBC). We investigated the effects of manure, chemical fertilizer and manure combined with biochar on soil physical-chemical properties, PNR, and the amoA gene abundance, diversity and structure of AOA and AOB in the rhizosphere. Our results showed that compared with CK treatment, CF and CFBC increases PNR by 19.3–34.7 % in the rhizosphere, M, MBC and FMBC decrease PNR about 60.0 %; CF and CFBC increased AOA amoA gene copies by 40.2–101.7 %, while M, MBC and FMBC treatments decreased it by 66.5–81.9 %, five fertilization treatments decreased the AOB amoA gene copy by 33.1–81.9 %. The redundancy analysis showed that chemical fertilizer and manure combined with biochar affects the population structure of AOA and AOB by pH, available phosphorus (AP), ratio of carbon to nitrogen (C/N), soil moisture content (SMC), nitrate nitrogen (NO3−-N) and ammonium nitrogen (NH4+-N) in the rhizosphere. The results of partial least squares indicated that pH, total nitrogen (TN), AOA amoA gene copy and AOA Shannon index were main factors affecting nitrification potential in the rhizosphere. Therefore, AOA dominates the ammonia oxidation process in the acid purple soil under the condition of chemical fertilizer and pig manure combined with rice husk biochar. Meanwhile, fertilization affected ammonia oxidation process by regulating soil pH and TN in lemon rhizosphere soil.