Effects of combined biochar and organic fertilizer on nitrous oxide fluxes and the related nitrifier and denitrifier communities in a saline-alkali soil.

This study intended to evaluate the combined effects of both biochar and organic fertilizer on nitrous oxide (N 2 O) fluxes and composition of nitrifier and denitrifier of saline-alkali soil. Therefore, four different treatments such as CK (only chemical fertilizer), B (only biochar), M (only organic fertilizer), BM (B:M = 1:1) were used in this experiment. The results showed that N 2 O emissions were decreased in B and BM treatments compare to the control. In contrast, N 2 O emissions were highest before day 12 but lowest after day 19 in M treatment compare to the control. Application of biochar, organic fertilizer and biochar plus organic fertilizer decreased the nirS and nirK genes copies and enhanced the nosZ gene copies which resulting in the lower N 2 O fluxes. The ammonia-oxidizing bacteria (AOB) amoA and nirK genes copies were significantly increased by organic fertilizer before day 12, leading to high N 2 O emissions. The genera Nitrosospira (AOB) and Nitrososphaera (ammonia-oxidizing archaea, AOA) assumed absolute superiority. Additionally, Nitrosospira (AOB) was also appeared in nirK -type denitrifiers, illustrating denitrification was carried out by nitrifiers. The genera Azospirillum (nirS), Burkholderia (nosZ) and Polymorphum (nosZ) were dominant in CK. There was only one dominant genus, Mesorhizobium (nosZ) in the B treatment. The genera Mesorhizobium (nirK), Azoarcus (nirS), Kocuria (nirS) and Pseudomonas (nosZ) occupied the main status in the M treatment. The relative abundance of Rhodanobacter (nirS) and Azospirillum (nosZ) were higher in the BM treatment compared with other treatments. Soil water content (SWC), pH, NH 4 +-N and NO 3 −-N were the main factors affecting AOB and denitrifiers, which influencing N 2 O emissions. Overall, combined application of biochar and organic fertilizer can reduce the N 2 O emission where AOB and nirK -type denitrifier were the main contributors to the N 2 O emission. Unlabelled Image • Combined application of biochar and organic fertilizer decreased the N 2 O emission. • Biochar plus organic fertilizer decreased the nirS and enhanced the nosZ abundances. • The genus Nitrosospira was the main contributor for N 2 O emission. • SWC, pH, NH 4 +-N and NO 3 −-N were the main factors affecting AOB and denitrifiers, and then influencing N 2 O emissions. [ABSTRACT FROM AUTHOR]