Modeling Belowground Complexity: Integrative Multivariate and Structural Analyses of Soil Nematode Communities Across the Climatic Gradient in Limpopo Grasslands

Soil nematode communities are valuable indicators of ecosystem functioning and soil food web structure. This study assessed the diversity, trophic composition, and ecological organization of nematode assemblages across four grassland sites in Limpopo Province, South Africa (Dalmada, Haenertsburg-top, Haenertsburg-down, and Sovenga Hills). A total of 31 nematode genera were identified, representing herbivores, fungivores, bacterivores, omnivores, and predators. Herbivores were the most diverse group, with Meloidogyne exhibiting the greatest individual biomass (86.99 µg), whereas bacterivores dominated numerically (43–63% of total abundance). The c–p spectrum ranged from colonizer–persister class 1 to 5. Higher structural maturity, indicated by greater representation of c–p 4–5 taxa, characterized Dalmada and Sovenga Hills, while Haenertsburg sites were dominated by opportunistic c–p 2 forms (88–100%). Ecological indices varied significantly among sites (p < 0.001). The Maturity Index was highest in Dalmada (2.08 ± 0.38) and Haenertsburg-top (2.35 ± 0.01), while Shannon diversity peaked in Dalmada (3.14 ± 0.01) and Sovenga Hills (2.85 ± 0.04). Food web analysis indicated enriched but structurally constrained systems, with high Enrichment Index values in Sovenga Hills (68.46 ± 18.63) and Dalmada (61.26 ± 20.26), contrasted with a low Structure Index in Haenertsburg-down (0). nMDS and RDA ordinations showed clear site-specific clustering associated with soil texture, pH, organic matter, and electrical conductivity. Structural equation modeling identified bacteria as a key driver, positively influencing omnivore–predators (β = 0.766) and negatively impacting herbivores (β = − 0.134). In conclusion, the grassland soils support moderately enriched but functionally differentiated nematode communities governed by local edaphic conditions.