Leaf Litter Fuels Methanogenesis Throughout Decomposition in a Forested Peatland

Decomposing leaf litter is a large supply of energy and nutrients for soil microorganisms. How long decaying leaves continue to fuel anaerobic microbial activity in wetland ecosystems is poorly understood. Here, we compare leaf litter from 15 tree species with different growth forms (angiosperms and gymnosperms, deciduous, and longer life span), using litterbags positioned for up to 4 years in a forested peatland in New York State. Periodically, we incubated partially decayed residue per species with fresh soil to assess its ability to fuel microbial methane (CH₄) production and concomitant anaerobic carbon dioxide (CO₂) production. Decay rates varied by leaf type: deciduous angiosperm > evergreen gymnosperm > deciduous gymnosperm. Decay rates were slower in leaf litter with a large concentration of lignin. Soil with residue of leaves decomposed for 338 days had greater rates of CH₄ production (5.8 µmol g^?1 dry mass d^?1) than less decomposed (<0.42 µmol g^?1 dry mass d^?1) or more decomposed (2.1 µmol g^?1 dry mass d^?1) leaf residue. Species-driven differences in their ability to fuel CH₄ production were evident throughout the study, whereas concomitant rates of CO₂ production were more similar among species and declined with degree of decomposition. Methane production rates exhibited a positive correlation with pectin and the rate of pectin decomposition. This link between leaf litter decay rates, biochemical components in leaves, and microorganisms producing greenhouse gases should improve predictions of CH₄ production in wetlands.