Strong N2O uptake capacity of paddy soil under different water conditions

Paddy field is a major global land use form. However, frequent fluctuations in soil water content make paddy fields important N2O emission sources. The contribution of N2O uptake to the reduction in net N2O emission from paddy soil varies with water content. Nevertheless, little is known about the impact of physicochemical factors, microbial regulatory mechanisms, and water content on N2O uptake in paddy soil. We designed and conducted a microcosm experiment controlled for gravimetric water content and applied exogenous N2O to three paddy soils differing in texture and parent material. During the incubation period, we monitored the headspace N2O content, measured the ammonia-N, nitrate-N, and dissolved organic carbon content, and analyzed the number of nosZ-containing microorganisms. For all three paddy soils, the total N2O uptake was > 50.71% at 20% gravimetric water content. The total N2O uptake increased exponentially (R2 ≥ 0.96) with water content throughout the incubation period. The highest N2O uptake range (73.94–78.44%) was detected at 70% gravimetric water content. Hence, paddy soil can absorb and consume abundant N2O at different water content, and prolonging the flooding period in the field could enhance the total N2O uptake. Furthermore, N2O uptake was strongly positively correlated with dissolved organic carbon consumption and increase in nosZ gene abundance (P < 0.001). Under various water content, the average N2O uptake in silty clay loam soil was 385.20 μg•kg−1 which was significantly higher than those for loam and sandy loam soils (351.98 μg•kg−1, P < 0.05). Moreover, nosZ gene abundance was substantially higher in SCL than the other soils. Future research should endeavor to determine the mechanisms by which NH4+-N content, pH, and organic carbon content affect N2O uptake in different types of paddy soil.