Biochar amendment suppresses N2 O emissions but has no impact on 15 N site preference in an anaerobic soil.

Abstract

Biochar amendments often decrease N2 O gas production from soil, but the mechanisms and magnitudes are still not well characterized since N2 O can be produced via several different microbial pathways. We evaluated the influence of biochar amendment on N2 O emissions and N2 O isotopic composition, including 15 N site preference (SP) under anaerobic conditions. An agricultural soil was incubated with differing levels of biochar. Incubations were conducted under anaerobic conditions for 10 days with and without acetylene, which inhibits N2 O reduction to N2 . The N2 O concentrations were measured every 2 days, the SPs were determined after 5 days of incubation, and the inorganic nitrogen concentrations were measured after the incubation. The SP values with acetylene were consistent with N2 O production by bacterial denitrification and those without acetylene were consistent with bacterial denitrification that included N2 O reduction to N2 . There was no effect of biochar on N2 O production in the presence of acetylene between day 3 and day 10. However, in the absence of acetylene, soils incubated with 4% biochar produced less N2 O than soils with no biochar addition. Different amounts of biochar amendment did not change the SP values. Our study used N2 O emission rates and SP values to understand biochar amendment mechanisms and demonstrated that biochar amendment reduces N2 O emissions by stimulating the last step of denitrification. It also suggested a possible shift in N2 O-reducing microbial taxa in 4% biochar samples.