Soil pH management for mitigating N2O emissions through nosZ (Clade I and II) gene abundance in rice paddy system

Abstract

Soil nitrous oxide (N2O) is produced by abiotic and biotic processes, but it is solely consumed by denitrifying microbes-encoded by nosZ genes. The nosZ gene includes two groups i.e. Clade I and Clade II, which are highly sensitive to pH. Managing pH of acidic soils can substantially influence soil N2O production or consumption through nosZ gene abundance. Nevertheless, the response of nosZ (Clade I and Clade II) to pH management needs elucidation in acidic soils. To clarify this research question, a pot experiment growing rice crop was conducted with three treatments: control (only soil), low dose of dolomite (LDD), and high dose of dolomite (HDD). The soil pH increased from 5.41 to 6.23 in the control, 6.5 in LDD and 6.8 in HDD treatment under flooded condition. The NH4+ and NO3− contents increased and reached the maximum at 30.4 and 21.5 mg kg−1, respectively, in HDD treatment under flooding condition. The contents of dissolved organic carbon and microbial biomass carbon showed a swift rise at midseason aeration and reached maximum at 30.7 and 101 mg kg−1 in the HDD treatment. Clade I, Clade II and 16S rRNA genes abundance increased with the onset of flooding, and occurred maximum in the HDD treatment. A peak in N2O emissions (5.96 μg kg−1 h−1) occurred at midseason events in the control when no dolomite was added. Dolomite application significantly (p ≤ 0.001) suppressed N2O emissions, and HDD treatment was more effective in reducing emissions. Pearson correlation, linear regressions and principal component analysis displayed that increased soil pH and Clade I and Clade II were the main controlling factors for N2O emission mitigation in acidic soil. This research demonstrates that ameliorating soil acidity with dolomite application is a potential option for the mitigation of N2O emissions.