Biological nitrogen fixation(BNF)can help replenish available nitrogen(N)in cropland and reduce the use of chemical N fertilizers,with diazotrophs playing an important role.However,the response of diazotroph community...Biological nitrogen fixation(BNF)can help replenish available nitrogen(N)in cropland and reduce the use of chemical N fertilizers,with diazotrophs playing an important role.However,the response of diazotroph community and BNF activity in biochar amendment soil,especially in the deep soil horizon,are poorly understood.In this study,soil samples were collected from topsoil(0-20 cm)and subsoil(20-40 cm)in the field experiment(established in 2013)comprising treatments with no chemical fertilizer(CK),chemical fertilizer(NPK),biochar(BC),and biochar plus chemical fertilizers(BNPK).Here,we investigated the diazotroph community using real-time PCR and high-throughput sequencing of the nifH gene,and assessed the soil N_(2)fixation rate(R_(Nfix))using acetylene reduction assay(ARA).Results showed that in the topsoil,the treatments with biochar significantly increased nifH gene copies and R_(Nfix),which was consistent with the increased soil organic matter(SOM),total carbon-to-nitrogen ratio(C/N),dissolved organic carbon(DOC)and pH.In the subsoil,applying chemical fertilizers(NPK)strongly decreased R_(Nfix),but had no effect on diazotroph abundance;in contrast,biochar application(BC)had no effect on R_(Nfix),but suppressed the growth of bacteria and diazotrophs while increasing the abundance of Rhizobiales order.Diazotroph and bacterial gene copies were significantly and positively correlated in both top-and sub-soil,and they were mainly influenced by SOM and total nitrogen(TN).In addition,soil nitrate nitrogen(NO_(3)^(−)-N)was the major factor in shaping the vertical stratification of diazotroph community structure.Although nifH gene abundance was significantly cor-related with R_(Nfix)in the topsoil,the structure equation modeling(SEM)showed the highest correlation between diazotroph community structure and R_(Nfix).Hence,we suggested that soil carbon and nitrogen sources were the key factors correlated with changes in the vertical pattern of diazotroph abundance.Biochar induced the dominant diazotroph community succes-sion and increased soil carbon content and pH,which contributed to the BNF activity.Changes in the BNF activity were driven by the variation in diazotroph community structure.展开更多
基金the National Natural Science Foundation of China(Grant No.31972511)the National Key R&D Program of China(Grant No.2018YFD0201001)China Agriculture Research System of MOF and MARA(CARS-13).
文摘Biological nitrogen fixation(BNF)can help replenish available nitrogen(N)in cropland and reduce the use of chemical N fertilizers,with diazotrophs playing an important role.However,the response of diazotroph community and BNF activity in biochar amendment soil,especially in the deep soil horizon,are poorly understood.In this study,soil samples were collected from topsoil(0-20 cm)and subsoil(20-40 cm)in the field experiment(established in 2013)comprising treatments with no chemical fertilizer(CK),chemical fertilizer(NPK),biochar(BC),and biochar plus chemical fertilizers(BNPK).Here,we investigated the diazotroph community using real-time PCR and high-throughput sequencing of the nifH gene,and assessed the soil N_(2)fixation rate(R_(Nfix))using acetylene reduction assay(ARA).Results showed that in the topsoil,the treatments with biochar significantly increased nifH gene copies and R_(Nfix),which was consistent with the increased soil organic matter(SOM),total carbon-to-nitrogen ratio(C/N),dissolved organic carbon(DOC)and pH.In the subsoil,applying chemical fertilizers(NPK)strongly decreased R_(Nfix),but had no effect on diazotroph abundance;in contrast,biochar application(BC)had no effect on R_(Nfix),but suppressed the growth of bacteria and diazotrophs while increasing the abundance of Rhizobiales order.Diazotroph and bacterial gene copies were significantly and positively correlated in both top-and sub-soil,and they were mainly influenced by SOM and total nitrogen(TN).In addition,soil nitrate nitrogen(NO_(3)^(−)-N)was the major factor in shaping the vertical stratification of diazotroph community structure.Although nifH gene abundance was significantly cor-related with R_(Nfix)in the topsoil,the structure equation modeling(SEM)showed the highest correlation between diazotroph community structure and R_(Nfix).Hence,we suggested that soil carbon and nitrogen sources were the key factors correlated with changes in the vertical pattern of diazotroph abundance.Biochar induced the dominant diazotroph community succes-sion and increased soil carbon content and pH,which contributed to the BNF activity.Changes in the BNF activity were driven by the variation in diazotroph community structure.
