Microbial Drivers of Litter Decomposition and Soil Carbon Pool Stability in Subtropical Agroforestry Systems Under Climate Change

Abstract:

Litter decomposition is a core ecological process regulating soil carbon (C) cycling in subtropical agroforestry systems (AFSs), and its response to climate change (e.g., warming and altered precipitation) directly affects soil C pool stability and ecosystem C sequestration capacity. Soil microbes (bacteria and fungi) are the primary drivers of litter decomposition, but the specific mechanisms by which microbial communities, functional genes, and enzyme activities regulate litter decomposition and soil C pool stability under climate change remain unclear. Here, we conducted a 4-year field manipulation experiment (warming + reduced precipitation) in three typical subtropical AFSs (poplar-soybean intercropping, citrus-grass intercropping, and Chinese fir-peanut intercropping) to explore the microbial drivers of litter decomposition and soil C pool dynamics. We combined litterbag decomposition experiments, high-throughput sequencing, quantitative real-time PCR (qPCR), and extracellular enzyme activity (EEA) assays to characterize litter decomposition rates, soil C pool components (labile C: DOC, MBC; stable C: SOC, recalcitrant C), microbial community structure, functional gene abundance, and EEA. Results showed that: (1) Warming + reduced precipitation significantly decreased litter decomposition rates by 18.2%-25.7% across all AFSs, with the strongest inhibition in poplar-soybean intercropping (low litter quality) and the weakest in Chinese fir-peanut intercropping (high litter diversity); (2) The reduction in decomposition was closely associated with changes in microbial community composition: fungal/bacterial ratio decreased by 32.1%-45.3%, and the relative abundance of lignin-degrading fungi (e.g., Trichoderma, Phanerochaete) and cellulose-degrading bacteria (e.g., Cellulomonas, Bacillus) significantly declined; (3) Functional gene abundance (ligninase gene: lcc; cellulase gene: cel48) and EEA (lignin peroxidase, cellulase, β-glucosidase) were significantly reduced under climate change, and these indices were positively correlated with litter decomposition rates (r = 0.78-0.86, p < 0.01); (4) Soil labile C pool (DOC, MBC) decreased by 15.6%-22.3%, while stable C pool (SOC, recalcitrant C) increased by 8.9%-13.2% under climate change, and the stability of soil C pool (recalcitrant C/SOC ratio) was negatively correlated with microbial functional potential (sum of lcc and cel48 gene abundance, r = -0.83, p < 0.01); (5) Chinese fir-peanut intercropping with high litter diversity had higher microbial diversity, functional gene abundance, and EEA, which alleviated the negative impact of climate change on litter decomposition and soil C pool stability. Our findings demonstrate that climate change inhibits litter decomposition by altering microbial community structure and reducing microbial functional potential, thereby increasing soil C pool stability in subtropical AFSs, and litter diversity is a key regulating factor. This study provides a new microbial perspective for predicting soil C cycling responses to climate change and optimizing AFS management to enhance C sequestration capacity.