Associations of vegetation, microbial communities, and soil properties with mineral-associated organic carbon in karst soils

Abstract

Mineral-associated organic carbon (MAOC) is an important component of stable soil carbon pools, yet its distribution and controlling factors in karst ecosystems remain unclear due to strong soil heterogeneity. This study investigated the relationships between vegetation type, microbial communities, soil physicochemical properties, and MAOC amount in a karst watershed in Guizhou, China. Surface soils (0–20 cm) were collected from limestone-derived Leptosols under three vegetation types: grassland, arboreal forest, and shrubland. Soil physicochemical properties were analyzed in combination with high-throughput sequencing of bacterial 16S rRNA genes and fungal ITS regions. MAOC content was highest in arboreal forest soils (5.54 g/kg), followed by shrubland (2.83 g/kg) and grassland (1.84 g/kg). Microbial richness and diversity did not differ significantly among vegetation types, although bacterial diversity was consistently higher than that of fungi. Dominant bacterial phyla included Proteobacteria, Acidobacteriota, and Actinobacteriota, while fungal communities were dominated by Ascomycota, with relatively higher abundances of Basidiomycota and Rozellomycota in arboreal forest soils. Soil chemical properties showed no significant differences among vegetation types, whereas soil texture varied significantly. Across the study area, MAOC was positively associated with Actinobacteriota abundance, soil pH, and sand content, and negatively associated with clay and silt contents. These findings indicate that MAOC variation in karst soils is closely associated with vegetation type, soil texture, and microbial community composition. Arboreal forest soils were associated with relatively higher MAOC levels, highlighting the importance of vegetation–soil–microbe interactions in soil carbon stabilization and ecosystem quality in carbonate landscapes.