Abstract: Soil microorganisms are central to litter decomposition, yet the functional role of phyllosphere microorganisms—the initial colonizers of senescing leaves—and their interaction with soil biota remain poorly understood. To disentangle their respective and combined contribution, we conducted a 12-month decomposition experiment with Pinus massoniana needle litter under three microbial treatments: NS (non-sterilized needles + non-sterilized soil), NSS (non-sterilized needles + sterilized soil), and SNS (sterilized needles + non-sterilized soil). The combined microbial community (NS) exhibited the highest decomposition rates, resulting in greater mass loss (~36%) and lignin loss (~33%) after 12 months than treatments containing either microbial source alone (NSS: ~26% mass loss, ~24% lignin loss; SNS: ~19% mass loss, ~17% lignin loss). This enhancement was attributable to functional complementarity between phyllopshere and soil microbial communities, expressed through stage-specific shifts in community composition and lignin degradation capacity. Co-occurrence network analysis further revealed treatment-specific microbial interaction patterns and highlighted key decomposer taxa, including Oidiodendron, Mycena, and Acidothermus. Microbial succession occurred throughout decomposition, while dominant decomposer-related phyla remained broadly consistent, with fungi largely dominated by Ascomycota (~84%) and bacteria mainly represented by Proteobacteria (~47%), Acidobacteria (~17%), Actinobacteria (~15%), and Firmicutes (~13%). Importantly, these shared taxonomic groups exhibited distinct temporal dynamics and interaction patterns across treatments. Overall, our results demonstrate that phyllosphere microorganisms actively contribute to litter decomposition and, through functional complementarity with soil biota, enhance decay process. These phyllosphere-soil microbiome interactions provide new mechanistic insights into microbial regulation of litter decomposition and nutrient cycling in forest ecosystems.

Key words: Pinus massoniana, phyllosphere, soil microbiome, litter decomposition, microbial succession