The litter layer acts as a moisture-induced bidirectional buffer for atmospheric methane uptake by soil of a subtropical pine plantation

•How litter layer controls atmospheric CH4 diffusion into the mineral soil is unclear.•We studied this issue in a pine forest under a wide range of soil water content.•Litter layer reduced atmospheric CH4 uptake when soil moisture below 15.8 vol%.•Litter layer enhanced atmospheric CH4 uptake when soil moisture above this value.•Litter layer acted as a moisture-induced bidirectional buffer for CH4 uptake by soil.

Forest soils are well known sinks for atmospheric methane (CH4), but how the surface litter layer controls gas diffusion into the mineral soil is still unclear. Seasonal rainfall in the humid climate provides a unique opportunity to examine uptake of atmospheric CH4 under a wide range of soil water content (SWC). We studied this question using a litter removal method in a 20-year-old slash pine (Pinus elliottii) plantation in subtropical China during 2005–2007. Soil-atmosphere CH4 fluxes of the control (FCK) and litter-free (FLF) treatments and their differences (litter-affected CH4 flux, FCK–LF = FCK − FLF) were all significantly influenced by SWC and not by soil temperature. Litter layer reduced atmospheric CH4 uptake by soil when SWC was below 15.8 vol%, and increased atmospheric CH4 consumption by soil when SWC was above this value. We concluded that the litter layer acts as a moisture-induced bidirectional buffer for atmospheric CH4 uptake by soils in a subtropical humid pine plantation. However, the removal of the litter layer had a minimal effect (+0.7%) on annual atmospheric CH4 uptake by soil, through compensating effects during the wet and dry seasons. Therefore, in the context of climate change, future changes in SWC will alter the strength of atmospheric CH4 uptake by soils of subtropical pine plantations.