Abstract

Biological nitrogen fixation (BNF) is strongly affected by the carbon (C) and nitrogen (N) stoichiometry in soil and depends on the input of organic C. Due to the high metabolic costs of nitrogenase activity, however, the response of BNF to organic C input and its impact on microbial turnover remain unclear. To address this knowledge gap, we combined 15N2 tracing with high-throughput sequencing by adding glucose or glucose plus mineral N fertilizer for a 12-day incubation in three cropland soils. Glucose addition alone strongly changed the BNF activity (0.76–2.51 mg N kg−1 d−1), while BNF was completely absent after mineral N fertilization. This switch-on of BNF by glucose addition supported equally high rates of microbial growth and organic C mineralization compared with the direct mineral N assimilation by microorganisms. Glucose-induced BNF was predominantly catalyzed by Azotobacter-affiliated free-living diazotrophs (>50 % of the total nifH genes), which increased with diverse nondiazotrophs such as Nitrososphaera, Bacillus and Pseudoxanthomonas. Structural equation models (SEMs) and random forest (RF) analyses consistently revealed that the soil C:N ratio and Azotobacter-affiliated diazotrophic abundances were the key factors affecting glucose-induced BNF. Our findings emphasize the importance of free-living diazotrophs for microbial turnover of organic C in soil.

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.