Methane emissions from rice paddies are regulated by carbon availability and soil pH along a mean annual temperature gradient

Abstract

Abstract Rice paddies are a major anthropogenic source of atmospheric methane (CH₄), yet the spatial pattern and underlying mechanism of CH₄ emissions from rice paddies across climatic gradients remain poorly understood. We collected and incubated 30 flooded paddy soils spanning tropical to temperate regions of China, quantified CH₄ emissions and explored their soil and microbial drivers. We discovered that cumulative CH₄ emissions exhibited pronounced geographical variability, with higher emissions in tropical soils (0.18–10.75 mg kg −1 ) than in temperate soils (0.07–0.17 mg kg −1 ), and were primarily regulated by dissolved organic carbon (DOC), DOC accounted for 36.0% of the variance in cumulative CH₄ emissions. Peak CH₄ emission rates were jointly influenced by DOC and microbial biomass carbon, together they explained 24.4% of the variance in peak CH₄ emission rates. The timing of peak emissions was governed by the slow degradation of particulate organic carbon (POC), POC accounted for 13.8% of the variance in the timing of peak emissions. Structural equation modeling (SEM) further revealed that soil pH and mean annual temperature (MAT) could indirectly regulate cumulative CH₄ emissions through affecting the accumulation of labile carbon and nitrogen pool, the model explained 63% of the spatial variation in cumulative CH₄ emissions in total. The indirect effect of MAT was 0.20, and the indirect effect of soil pH was − 0.26. These results highlight the critical role of climate–soil-microbe interactions in shaping regional patterns of methane emissions from rice paddies and provide mechanistic insights for improving CH₄ emission predictions under future climate change.