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

Abstract

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 ¹⁵N-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.