Dynamics of salt marsh biomes in response to inundation

This thesis aims to increase our understanding of how the tripartite interaction between plant-animal-microbiota responds to an environmental change, i.e., inundation frequency. Particularly, this thesis focuses on the interactions among three community components of the late-successional stage of a salt marsh ecosystem in Western Europe. These key players are the tall grass Elytrigia atherica (Sea couch), the burrowing litter-feeding amphipod Orchestia gammarellus, and microbes, i.e., the plant and amphipod associated microbiota and soil microbiota. The results showed that salt marsh elevation, as a proxy of inundation frequency, was an important driver of soil properties, affecting both macro- and microbiota. However, the impact of the environmental changes associated with elevation varied depending on the organism, affecting their bacterial communities. On the one hand, the bacterial composition from the digestive tract of O. gammarellus was not significantly affected by elevation, which may be related to the low impact of the local environment on host life history and tolerance traits. On the other hand, elevation had a strong effect on E. atherica traits, rhizosphere, and root endosphere bacterial community composition. Furthermore, the interaction of O. gammarellus with E. atherica affected the taxonomic and functional components of soil bacterial communities differently compared to each component separately. Altogether, this thesis highlights the importance of including macroorganisms in soil microbial studies and vice versa since their response to disturbances are intimately linked to each other.