Mixed Litter Decomposition Drives Functional Gene Rearrangement in the Microbial Carbon Cycle

Abstract

Understanding how mixed‐species litter decomposition regulates microbial communities and carbon cycling is vital for guiding ecosystem restoration and climate change mitigation, as it is a key process for nutrient cycling and carbon sequestration. A 15‐month field experiment compared single‐species ( Pinus sylvestris var. mongolica [Ps], Populus × canadensis[Pc]) and mixed (PcPs) litters using metagenomics to analyze microbial communities and carbon cycle genes (KO01200). Metagenomic sequencing revealed significant differences in microbial community composition and carbon cycle‐related functions. Carbon metabolism genes accounted for 12.93% of the total sequenced genes, with Bacteria dominating these genes (97.23%–99.76%). In contrast, Archaea, Eukaryota, and Viruses showed lower relative abundances in carbon metabolism. Microbial diversity increased (e.g., Simpson and Shannon indices), but richness decreased (ACE and Chao1 indices). Beta diversity analysis showed significant differences among treatments, with principal coordinates analysis (PCoA) explaining 72.4% of variation in community structure and 80.9% in functional classification. A total of 352 microbial species exhibited significant differential abundance, including 20 species with LDA scores > 4. Specifically, the relative abundance of Proteobacteria increased in mixed litter (PcPs) compared to single species, with a significant difference between Pc and PcPs ( p  < 0.05). Functional analysis revealed 20 carbon cycle units with altered abundance: Photosystems I/II (psa/psb) peaked in mixed litter, while fermentation dominated in Ps. Mixed litter restructuring enhanced photosynthetic genes and reduced fermentation, shifting metabolism toward carbon sequestration via increased diversity and Proteobacteria dominance. Findings inform soil carbon management in degraded forests.