Soil Microbial Assembly Mirrors a Savanna Mosaic Amid Plant Invasion and Soil Disturbance

Savannas, spanning 20% of the Earth's surface, are characterized by a continuous grass matrix interspersed with woody patches, supporting high biodiversity and providing ecological and economic services. Although climatic and edaphic controls on savanna structure are well studied, the contribution of soil microbial communities in maintaining spatial heterogeneity and coexistence remains poorly understood. We investigated whether savanna heterogeneity is mirrored belowground and how disturbance and invasion by Megathyrsus maximus can modify these relationships. We used a factorial field sampling design in a mesquite savanna to compare woody patches and adjacent grasslands with and without mechanical disturbance and invasion. We quantified soil physicochemical properties, plant community composition, and bacterial and fungal communities to evaluate linkages among vegetation and soils. Grasslands and woody patches supported distinct soil and microbial assemblages, consistent with differences in vegetation inputs and nutrient regimes. Grassland microbial communities exhibited relatively simple assembly patterns, with plant diversity and soil chemistry serving as the primary correlates of community composition and stronger associations observed for fungi than bacteria. In woody patches, soil physicochemical properties were the primary correlates of microbial community composition, with plant diversity exhibiting weaker associations than in grasslands. In grasslands, invasion by M. maximus was associated with higher soil nutrient availability and shifts in microbial community composition, and mechanical disturbance correlated with similar but weaker effects. These shifts aligned with reduced grassland microbial distinctiveness and may disrupt linkages between vegetation, soils, and microbes. Aboveground patch structure in savannas aligned with belowground microbial communities and nutrient dynamics. By demonstrating that invasion and disturbance weaken these spatial patterns, this study indicates that soil microbial communities may contribute to savanna coexistence and resilience, revealing a possible association between belowground community assembly and landscape-scale heterogeneity and its destabilization under multiple stressors.