The addition of chemical compounds extracted from leaf litter leachates enhances short term methane uptake by forest soils

Upland forest soils are recognized as the primary biological sink for methane. The influence of litter on soil methane uptake has not been clearly elucidated: litter could reduce methane uptake, have no influence or enhance it. Until now, the role of litter has only been studied for the diffusion of gases. The chemical influence of leachate compounds from litter is a dominant process in forest ecosystems. In this study, we investigated this influence on soil methane fluxes. We extracted leaf litter compounds from four temperate tree species (beech, oak, pine and spruce) and determined their biochemical composition by spectrophotometry. The leachates, or pure water for the control treatment, were added to three different types of sieved forest soil (alocrisol, cambisol and luvisol) to determine their influences on methane fluxes. The methane fluxes were monitored for 48-h. We found that the chemical compounds leached from leaf litter enhanced methane uptake by 8.2 % with no significant effect of the species from which the leachates were extracted. The enhancement depended on the type of soil and was correlated to initial methane uptake. These results indicate that the role played by litter in the methane balance of forest soils, which has so far been thought to affect only the availability of the substrate (methane and dioxygen), is more complex than that.