The effect of long-term biochar amendment on N_2O emissions: Experiments with N~(15)-O~(18) isotopes combined with specific inhibition approaches

摘要

Numerous studies reporting a transient decrease in soil nitrous oxide (N_2O) emissions after biochar amendment have mainly used short-term experiments. Thus, long-term field trials are needed to clarify the actual impact of biochar on N_2O emissions and the underlying mechanisms. To address this, both a ~(15)N-~(18)O labeling technique and gene analyses were applied to investigate how N_2O production pathways and microbial mediation were affected by long term biochar amendment in field. Then, 1-octyne and 2-phenyl 1-4,4,5,5-tetramethylimidazoline-l-oxyl 3-oxide (PTIO) were used in combination with potassium chlorate to evaluate the relative contribution of ammonia-oxidizing bacteria (AOB) and archaea (AOA) to potential ammonia oxidation (PAO) and the associated N_2O production. Acidic and alkaline greenhouse vegetable soils that had each received two separate treatments were collected (control, no biochar amendment; biochar, biochar amended in the field after 2 ox 1 years). The results showed that biochar decreased N_2O emissions by 48% in acidic soils and by 22% in alkaline soils compared to those in control. These results were explained by decreases in nitrifier denitrification- (by 74%) and het-erotrophic denitrification-derived N_2O production (by 58%), as further evidenced by a decrease in N_2O~-(by 87%) and the (nirK+nirS+fungal nirK)：(nosZ-Ⅰ + nosZ-Ⅱ) ratio (by 5%) in both greenhouse vegetable soils. However, biochar increased nitrifier nitrification-derived N_2O in both soils because of increases in pH and PAO, which were attributed to an increased abundance of AOB rather than AOA. The contribution of AOB to PAO (or N_2O) exceeded 69% (or 68%) of the total in acidic soil and 88% (or 85%) of the total in alkaline soil after biochar amendment. Our findings demonstrated that the mitigation of N_2O by biochar is linked to specific N_2O production pathways.