Soil carbon dynamics shape bacterial communities across grassland and agricultural soils with implications for phosphorus

Introduction Phosphorus (P) is a critical nutrient influencing soil fertility, yet its role in shaping bacterial community structure remains underexplored, particularly in native grasslands versus agricultural systems. This study aimed to evaluate how bioavailable P and other edaphic factors influence soil bacterial communities across contrasting land-use types. Methods Soil bacterial communities were assessed using 16S rRNA gene-based amplicon sequencing at two contrasting sites in northeast Kansas, USA: native tallgrass prairie at Konza Prairie Biological Station (KPBS) and agricultural soils at Hays. In parallel, geochemical profiling was conducted to quantify bioavailable P and other soil physicochemical properties. Results Soil bacterial abundance, diversity, and community composition differed significantly between native grassland and agricultural soils. Bacterial abundance was higher in grassland soils (p < 0.05) and positively correlated with soil organic matter (SOM), K + , and Mg 2+ . In contrast, alpha diversity metrics (ASV richness and Faith’s Phylogenetic Diversity) were greater in agricultural soils and negatively correlated with water-extractable soil organic carbon (WE-SOC, p < 0.05), suggesting that excess labile carbon may reduce diversity or reflect indirect land-use effects. Beta diversity analyses revealed distinct community composition between sites, primarily structured by WE-SOC (r 2 = 0.41), soil moisture (r 2 = 0.52), and pH (r 2 = 0.43), with a smaller contribution from labile P forms (r 2 = 0.21). Although specific taxa responded to P pools, soil P did not emerge as the dominant driver of overall microbial community structure. Discussion These findings indicate that anthropogenic land-use changes, such as agriculture, influence soil microbial communities primarily through broader physicochemical shifts rather than direct phosphorus enrichment. This highlights the indirect role of P within a complex network of soil properties governing microbial ecology.