Hydrological regime and niche partitioning drive fungal community structure and function in arid wetlands sediments of South Africa

Arid wetlands are ecologically significant yet understudied ecosystems shaped by extreme conditions and hydrological variability. However, the structure and ecological functional of fungal communities in these habitats remain poorly understood, especially in southern Africa. This study integrated shotgun metagenomics, FUNGuild functional profiling, and multivariate analyses to examine fungal diversity, functional composition, and environmental drivers in seasonal and permanent arid wetlands of South Africa. Distinct fungal assemblages emerged, primarily shaped by hydrological regimes and ionic stress. Seasonal wetlands were dominated by Mucoromycota (79%), particularly arbuscular mycorrhizal (AM) fungus (Rhizophagus, 62%), while permanent wetlands had higher Ascomycota (54%), with Aspergillus (50%) prevalent in oxygen-limited sediments. Although alpha diversity showed no significant difference, beta diversity confirmed significant mycobiome differentiation. Total dissolved solids (TDS), electrical conductivity (EC), and salinity were key predictors of fungal composition, with TDS the strongest determinant (p < 0.01). Functional guild analysis highlighted niche differentiation, with saprotrophs dominating permanent wetlands (59.7% vs. 21.5%; p < 0.05), while symbiotrophs, particularly AM fungi, were enriched in seasonal wetlands (69.3% vs. 36.1%; p < 0.001). Indicator taxa identified via LefSe (LDA > 3, p < 0.05) and random forest modeling included Rhizophagus, Trichoderma, Fusarium, and Entomophthora in seasonal wetlands, and Aspergillus in permanent wetlands. This study provides the first integrative insight into fungal ecology in South Africa's arid wetlands, demonstrating that hydrological regime shapes fungal structure and function through environmental filtering and niche specialization, with implications for guiding conservation and adaptive management of these fragile ecosystems.