The roles of litter quality and microbial processing in shaping leachate chemodiversity during early decomposition

Early litter decomposition is a critical juncture in the terrestrial carbon cycle, when plant-derived dissolved organic matter (DOM) is first liberated and transformed prior to entering soil. Although litter quality and environmental conditions are known to influence DOM quantity, the joint roles of abiotic tissue disruption and decomposer community composition in structuring DOM chemodiversity remain largely conceptual. We addressed this gap by varying litter quality, the relative strength of abiotic versus biotic degradation pathways, and decomposer populations across nine chemically distinct forest litter types in five-day incubations. By manipulating microbial activity (± sodium azide) and decomposer source (phyllosphere-only versus soil-inoculated), we tested whether litter quality governed DOM release, whether microbial activity enhanced DOM production and homogenized chemodiversity relative to abiotic degradation, and whether greater decomposer diversity is associated with increased chemodiversity. Across litter types, initial chemical differences strongly influenced the quantity of DOM released (234 – 508 mg C g⁻ 1 litter-C) but weakly predicted molecular chemodiversity. Microbial activity generally reduced net DOM release (−11 – −31 %) in cold and warm water incubations, but enhanced DOM release under freeze–thaw conditions (+20 %). Contrary to expectations, microbial processing did not homogenize bulk DOM chemodiversity, despite shifts in amino acids and phenolics. Soil microbial inoculation consistently altered decomposer community composition and increased evenness but had only modest effects on chemodiversity. Together, these results demonstrate that the initial pulse of DOM into soils is primarily constrained by source litter chemistry, with microbial activity and community origin acting as secondary modifiers.