Abstract
Litter decomposition is an important process of nutrient cycling and is primarily driven by microbes. However, whether the microorganisms in decomposing litter come from the phyllosphere or soil is still unclear. In this study, we collected litter of two dominant species in a temperate forest, Fraxinus mandshurica and Pinus koraiensis (newly shed, and decomposing litter in the early-stage and late-stage) and surrounding soil to approach this question. Our results suggested that in the early-stage of decomposition, phyllosphere bacteria utilized readily available substances, preempting the niche of soil bacteria, while soil fungi were able to invade the litter through hyphae and spores. These activities further modified the ecological niche in the decomposing litter, facilitating the subsequent entry of soil bacteria and fungi. The timing of soil microbial invasion was influenced by litter quality. In the low-quality litter, the resource limitation hindered the entry of soil microorganisms and consequently slowed down the decomposition process. These findings offer crucial insights for better understanding of the litter decomposition process during which substantial carbon is lost from the ecosystem.