Biochar and organic fertilizer changed the ammonia-oxidizing bacteria and archaea community structure of saline-alkali soil in the North China Plain

Purpose The application of a large amount of inorganic nitrogen (N) fertilizer resulted in an increasing N loss. It is an effective practice that biochar and organic fertilizer replace part of inorganic nitrogen fertilizer. Thus, it is necessary to identify and compare the effects of biochar and organic fertilizer on ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) community structure in saline-alkali soil. Materials and methods Three treatments in triplicate were included in the field experiment: (1) CK (no biochar and organic fertilizer), (2) biochar at 10.0 t ha(-1) year(-1) (C), and (3) organic fertilizer at 7.5 t ha(-1) year(-1) (M). The community structures and diversities of AOB and AOA were investigated by Illumina sequencing analysis of gene encoding ammonia monooxygenase subunit A (amoA) and followed by principal component analysis, least discriminant analysis effect size, and redundancy analysis. Results and discussion Biochar and organic fertilizers did not change the diversity of AOA and reduced the relative abundance of Candidatus-Nitrosoarchaeum in maize season, while only biochar increased the relative abundance of Candidatus-Nitrosotenuis in wheat season. The diversity of AOB was significantly reduced in the M treatment, but was not changed in the C treatment in wheat season. Moreover, the relative abundances of Nitrosomonas (CK, 15.1%; C, 6.8%; M, 3.4%) were decreased in the maize season, and the relative abundances of Nitrosovibrio (CK, 9.8%; C, 16.8%; M, 14.5%) were increased in the wheat season in the C and M treatments, which probably related to the changes in soil pH, soil NH4+-N content, and soil salt content (SSC). The lower soil pH, higher NO3--N content, and SSC resulted in Nitrosospira (maize season: CK, 42.2%; C, 40.7%; M, 62.0%; wheat season: CK, 46.6%; C, 50.7%; M, 65.4%) becoming the dominant genus in the M treatment. Conclusions Our results indicated that AOB was more susceptible than AOA to biochar and organic fertilizer. Organic fertilizer has significant effects on the diversities and community structure of AOB than biochar associated with the changing in soil pH, salinity, and mineral N.