Abstract: Methane (CH₄) is the second important anthropogenic greenhouse gas after carbon dioxide (CO₂). Forest soils are a sink for atmospheric CH₄ and play an important role in modulating global CH₄ budget. Litter is important carbon and nutrient sources for forest soils. Litter decomposition could increase soil carbon and nutrient concentrations and reduce oxygen concentration beneath the soil surface as well as the oxidation and diffusion of soil CH₄. However, it remains unclear whether litter input changes CH₄ uptake in forest soils. In this study, a microcosm experiment was conducted in a subtropical forest, and soil CH₄ flux under the conditions with and without litter input was monitored monthly by chambers in a Chinese fir (Cunninghamia lanceolata) plantation over one year. We found that litter removal significantly increased soil CH₄ uptake in Chinese fir plantation. We further analyzed the changes in soil CH₄ flux after litter removal (leaf and root) and double litter input at six forest sites in other climatic zones. We found that litter removal significantly increased soil CH₄ uptake in broadleaved forests by 16.5%. On the contrary, double litter input decreased soil CH₄ uptake by 11.1% and 20.0% in broadleaved and coniferous forests, respectively, suggesting that the function of CH₄ sink in forest soils decreased with additional litter input. Our results suggest that litter input is an important factor affecting CH₄ flux uptake in forest soils, and that litter layers may reduce atmospheric CH₄ uptake by forest soils through reducing the oxygen concentration beneath soil surface.

Key words: litter addition, litter removal, CH₄ flux, greenhouse gas