Aridity level and hillslope aspect shape soil fungal diversity, functioning, and network organization in drylands

We examined soil fungal communities in southern Israel, and investigated the effects of aridity level (semi-arid, arid, and hyper-arid regions), hillslope aspect (north-vs. south-facing) and microhabitat (shrubs, inter-patch spaces, and livestock trampling routes). Our results revealed that aridity level and hillslope aspect influenced fungal community. Fungal species richness declined from 631 operational taxonomic units (OTUs) in the semi-arid site to 49 in the hyper-arid site. Aridity was the main factor structuring fungal community, whereas hillslope aspect had a smaller effect. Network analysis showed that fungal connectivity decreased with increasing aridity. However, this decline was not linear. The semi-arid system – particularly on south-facing hillslopes – showed stronger connectivity and more cohesive network structure, suggesting enhanced biotic interactions under moderate stressors. In contrast, the hyper-arid site maintained high numbers of nodes and edges but exhibited reduced clustering and weak connectivity, indicating diffuse and poorly structured interactions. Across all sites, high modularity indicated persistent niche partitioning, while the identity of highly connected taxa varied markedly, reflecting strong environmental filtering and functional turnover along the gradient. The findings indicate that increasing aridity shifts fungal communities from interaction-driven systems to stress-driven and stochastic assemblages, highlighting the vulnerability of soil microbiomes to climate change.