Effects of biochar addition on denitrification product ratio N2O/(N2O+N2) under different soil moisture: A 15N tracing experiment

Denitrification product ratio N 2 O/(N 2 O+N 2 ) is an important indicator reflecting the degree of N 2 O production and consumption, yet the mechanism of biochar application on denitrification products under different moisture in vegetable fields remains unclear. To clarify this issue, a 21-day 15 N-labeled experiment that incubated cinnamon soil was conducted to explore the effects of corn straw biochar addition on N 2 O/(N 2 O+N 2 ) at different water filled pore space (WFPS) levels, with 6 treatments: W 1 (65% WFPS+K 15 NO 3 ); W 1 B (W 1 +biochar); W 2 (80% WFPS+K 15 NO 3 ); W 2 B (W 2 +biochar); W 3 (95% WFPS+K 15 NO 3 ); W 3 B (W 3 +biochar). The results showed that compared with W 2 and W 3 treatments, 15 N 2 O emissions in W 2 B and W 3 B treatments reduced by 14.5% and 23.1%, 15 N 2 emissions increased by 16.9% and 24.4%, and N 2 O/(N 2 O+N 2 ) decreased by 20.9% and 33.4%, respectively. As moisture increased, compared to W 1 B treatment, 15 N 2 emissions of W 2 B and W 3 B treatments increased by 23.9% and 51.7%, respectively. Compared with W 1 B and W 2 B treatments, N 2 O/(N 2 O+N 2 ) in W 3 B treatment reduced by 19.0% and 24.9%, respectively. Biochar addition and the increased moisture improved denitrification rate by 8.4%~35%. Under 95% WFPS, biochar addition reduced nirK gene abundance by 16.7% and increased nosZ gene abundance by 25.3%. The mantel test implied that soil pH, NO 3 - content and dissolved organic carbon (DOC)/NO 3 - ratio were the factors influencing N 2 O/(N 2 O+N 2 ), and NO 3 - content and soil water content (SWC) were the factors influencing denitrifying microorganism. Overall, biochar addition under 95% WFPS caused the greatest decrease in N 2 O/(N 2 O+N 2 ). Our study provided new theoretical support for water management and N 2 O reduction in vegetable fields.