Heterotrophic nitrification and denitrification are the main sources of nitrous oxide in two paddy soils

Aims Paddy soil is one of the main sources of global nitrous oxide (N2O) emissions via multiple pathways regulated by different microbes. However, the relative contributions of N2O production pathways with the addition of organic carbon (C) in different paddy soils are poorly understood. Methods N-15-stable isotope and acetylene (C2H2) inhibition were used to differentiate the relative contributions of autotrophic and heterotrophic nitrification (ANF and HNF) and denitrification (DNF) to N2O emissions in two paddy soils (acid vs. neutral soil) with glucose addition. Results HNF and DNF were the main N2O pathways which contributed between 85% to 100% of the total N2O production at 70% water filled pore space. Low soil pH inhibited soil nitrification and the activity of ammonia oxidizers compared with neutral paddy soil. Glucose reduced nitrification rate and stimulated N2O production significantly, mainly via DNF in the two paddy soils. Moreover, glucose increased the relative contribution of DNF to total N2O production in the first 7 days and total N2O amounts from HNF over the 14-day incubation. Conclusions HNF and DNF rather than ANF dominated the N2O emissions regardless of soil pH. Glucose had a positive effect on N2O emissions by influencing HNF and DNF.