Microbial Dynamics and Competition in the Rhizosheath-Root Niche of Desert Plants

In arid desert ecosystems, xerophytic speargrasses have evolved unique adaptations, such as rhizosheath root systems, to optimise water and nutrient uptake. These systems create mini-oases with enriched resources that attract diverse edaphic microorganisms. However, according to the Darwinian ‘Survival of the Fittest’ theory, intense competition may occur among edaphic microorganisms to colonise such a favourable niche: only microorganisms equipped to sustain their own survival and favour the host fitness can succeed. Indeed, while the microbial communities in non - vegetated soils predominantly exhibit an autotrophic lifestyle, those associated with rhizosheath are primarily composed of heterotrophic beneficial bacteria enriched in antibiotic resistance genes and CRISPR-Cas motifs. These results support the hypothesis that the colonization of the rhizosheath triggers an intense microbial ‘Arms Race’ able to control the microbial biomass and promote the selection of beneficial microorganisms that mediate host resilience in a win-win interaction. Leveraging Darwin’s evolutionary theory, we further postulate that these dense and competitive niches serve as evolutionary hotspots that can drive the emergence of novel adaptive microbial strategies crucial for holobiont homeostasis in extremely harsh and inconsistent environmental conditions of deserts, including those arising from climate change scenarios.