Temperature-dependent inhibition of methane oxidation by ammonium in paddy soils

Abstract

Rice paddy soils are major sources of atmospheric methane emissions, contributing significantly to global warming. Methane oxidation by microbes regulates methane release from soils, but the process is influenced by temperature and nitrogen status. However, the interactive effects of temperature and ammonium on methane oxidation remain poorly understood, particularly across different climatic contexts. This study examined the effects of ammonium addition on methane oxidation and microbial dynamics during aerobic incubation at 15, 25, and 35 °C using paddy soils from three climatic zones. Increasing incubation temperature from 15 °C to 25 °C or 35 °C accelerated the initiation of methane oxidation, shortening the lag phase by 37–72%. In contrast, maximum methane oxidation rates varied only slightly across the tested temperature range (25–35 °C), but showed a positive relationship with the mean annual temperature of each climatic zone. The degree to which ammonium inhibited methane oxidation was strongly temperature dependent: the effect was only significant at 25 °C and 35 °C. This coincided with reductions in pmoA gene abundance and shifts in methanotrophic community composition, including a reduction in type II methanotrophs and an enrichment of type I methanotroph subgroups. Notably, the responses of type I subgroups to ammonium varied among soils, with type Ib and type Ia enrichment in tropical and temperate soils, respectively. Overall, these results indicate that temperature regulates the onset of methane oxidation and its sensitivity to ammonium, suggesting that warming may enhance the suppressive effects of nitrogen fertilisation on methane mitigation in rice paddies.