Organic-inorganic composite inoculant promotes carbon stabilization in acidic lateritic red soil by redirecting microbial catabolism toward anabolism.

Acidification, nutrient deficiency, and poor carbon pool stability are key bottlenecks restricting the sustainable development of agriculture in lateritic red soils. In this study, we isolated strains GC05 (Paracoccus communis) and GC07 (Advenella kashmirensis). A composite microbial consortium was constructed and then combined with a biochar-montmorillonite-chicken manure carrier to produce an organic-inorganic composite microbial inoculant. After applying the inoculant to acidic lateritic red soil, we investigated its mechanisms in simultaneously ameliorating acidic lateritic red soil and driving soil organic carbon stabilization. After a 30-day incubation, the inoculant ameliorated the soil environment and enhanced both nutrient availability and carbon stability. Soil pH increased from 4.86 to 5.76, the ratio of recalcitrant carbon to total organic carbon increased from 0.72 to 0.86. The inoculant promoted the enrichment of carbon assimilation-dominant functional microbial taxa. Microbial carbon use efficiency increased from 0.02 to 0.41, and the metabolic focus shifted from enzymatic depolymerization and catabolism to biomass synthesis and anabolism. Structural equation modeling further suggested that microbial biomass exerted a dominant direct effect on the stable soil carbon pool, driving the conversion of labile organic carbon into recalcitrant organic carbon via biomass synthesis and microbial necromass accumulation, which constituted an early-stage microbial carbon pump. This study provides a theoretical foundation and practical strategy for the development of bioaugmented technologies with potential for long‑term carbon sequestration in acidic lateritic red soils.