Biotic versus abiotic factors shaping culturable root endosymbionts of the saltmarsh halophyte, Batis maritima and implications for plant stress tolerance

Coastal marshes face increasing pressures from climate-related environmental stressors, adversely affecting their biota like plants and microbes. Understanding how marsh communities are influenced by their environment is critical in determining their ability to respond to environmental stressors. Plants harbor microbes that colonize and inhabit their tissues without causing apparent harm (‘endosymbionts’). These endosymbionts provide benefits to host plants including mediation of salinity stress response, thus it is important to understand the factors influencing the diversity of endosymbiont communities. We examined the relative influences of biotic (host-related) and abiotic (local environment) factors on the endosymbiont communities associated with the dominant saltmarsh halophyte, Batis maritima. Using culture-based and genetic approaches, we characterized both fungal and bacterial endosymbionts from B. maritima roots in Oso Bay, Texas, along the Gulf of Mexico. Isolation frequency of endosymbionts significantly differed between fungi and bacteria, and the overall diversity was low. Belowground plant biomass and salinity correlated with decreased diversity in fungi, while shifts in fungal composition varied according to light availability. Overall, these findings highlight the relative influences of both biotic and abiotic factors in shaping the root endosymbionts and might differ between fungi and bacteria. Understanding these processes is fundamental to determining the resilience of both endosymbionts and host plants, with implications for ecosystem functions amidst environmental pressures. As anthropogenic-driven environmental changes continue to rise, insights gained from these results can inform future coastal restoration and management especially of at-risk coastal ecosystems.