Seven years of wetter and delayed wet season enhanced soil methane uptake during the dry season in a tropical monsoon forest

Tropical monsoon forest soils have the potential to mitigate global warming by removing methane (CH4) from the atmosphere, yet whether this function would be altered under future precipitation regimes remains unclear. In this study, we conducted two rainfall manipulation treatments, including the delayed wet season (DW) and wetter wet season (WW), since 2012 in a tropical monsoon forest in southern China to investigate the impact of changing precipitation patterns on soil CH4 uptake over two measurement years between 2018 and 2019. We found that DW significantly increased the annual average soil CH4 uptake by 164%, mainly due to a significant increase during the dry season via enhancing soil moisture and soil enzyme activities. Although WW exerted a limited impact on the annual average soil CH4 uptake, it remarkably increased CH4 uptake during the dry season due to the alteration of soil temperature, nutrient conditions, and enzyme activities. Furthermore, we found that methanotrophic abundance increased and decreased with soil moisture during the dry and wet seasons, respectively. The optimum air-filled soil porosity for CH4 uptake was 0.45 m(3) m(-3). Our results suggested that the role of tropical monsoon forests as CH4 sinks would be enhanced under delayed wet season, which should not be overlooked for determining the global CH4 uptake capacity of forest soils in the future.