Historical contingencies linked to past drought-wetting cycles as a driver of bacterial–not fungal–community assembly processes in an arid desert

Abstract

Abstract Soil microbial communities are complex and dynamic, and their composition is jointly driven by niche and neutral processes. Otherwise, the assembly processes of these communities are known to be influenced by both biotic and abiotic factors, yet the extent to which past events could explain their contemporary composition remains unclear, particularly in natural desert environments. We used a phylogenetic framework to quantify the deterministic and stochastic community assembly processes of bacteria and fungi facing historical contingencies linked to past short- and long-term drought-wetting cycles. We found that deterministic and stochastic processes underpinned bacterial community assembly, while fungal communities were mainly assembled via stochastic processes. Abundant bacterial species were at the origin of the differences in phylodiversity noted between natural sites and those facing historical contingencies, while rare fungal species were at the origin of these differences. Furthermore, we showed that historical contingencies increased selection while decreasing dispersal limitation and homogeneous dispersal of bacterial communities. Yet fungal communities were found to be unaffected by past events and their assembly was constantly supported by stochastic processes. These results shed light on the differential impacts of historical contingencies on both bacteria and fungi. They also provide crucial information that could contribute to enhancing desert ecosystem resilience and conservation, and improving our comprehension of soil microbial community assembly in desert ecosystems.