The influence of soil temperature, methanogens and methanotrophs on methane emissions from cold waterlogged paddy fields.

Paddy fields are major sources of atmospheric methane (CH). However, CH emissions from cold-waterlogged paddy fields, a major type of paddy soil in China, remain unclear. Here we investigated the CH emissions and associated influential factors in cold-waterlogged paddy fields at two sites (Yangxin County and Daye City) in Hubei Province, South China. Normal paddy fields matched with parental material and cropping system were used as the controls. The CH emissions from cold-waterlogged fields were significantly higher than those from normal fields with (3.0-4.4-fold) or without (3.5-8.6-fold) rice. Rice planting increased CH emissions by 59-78% in cold-waterlogged fields and by 85-247% in normal fields. CH instantaneous fluxes were positively correlated with soil temperature and methanogen mcrA (methyl coenzyme M reductase alpha subunit) and methanotroph pmoA (methane monooxygenase) copy numbers at the annual scale. Under rice planting, mcrA copy number was higher in cold-waterlogged fields than in normal fields at both sites, whereas pmoA copy number had the same trend at the Daye site only. Soil temperature and water content influenced mcrA and pmoA copy numbers in the normal paddy fields, whereas soil organic matter content was more influential in the cold-waterlogged paddy fields. These findings suggest that perennial waterlogging is a prerequisite for substantial CH emissions from cold-waterlogged paddy fields, and it promotes the proliferation of methanogens and methanotrophs under rice planting. Therefore, CH production-oxidation processes are more active in cold-waterlogged paddy fields than in normal paddy fields.