The influence of host-plant connectivity on fungal assemblages in the root microbiota of Brachypodium pinnatum

Dispersal limitation may drive the structure of fungal microbiota of plant roots at small spatial scales. Fungal root microorganisms disperse through the plant rooting systems from hosts to hosts. Due to a pronounced host-preference effect, the composition of endophytic root microbiota may follow plant distribution. A given plant community may hence include a matrix of host-plant species that represent various habitat permeabilities to fungal dispersal in the floristic landscape. We experimentally tested the effect of host-plant isolation on endophytic fungal assemblages (Ascomycota, Basidiomycota, Glomeromycotina) inhabiting Brachypodium pinnatum roots. We calculated host-plant isolation using Euclidean distance (distance-based dispersal limitation) and resistance distance (functional-based dispersal limitation), based on host presences. All fungal groups were more influenced by the resistance distance between B. pinnatum than by the Euclidean distance. Fungal dispersal was hence strongly related to the spatial distribution of the host plants. The fungal groups displayed however different responses (in richness, abundance, and composition) to host isolation. Additionally, fungal assemblages were more strongly controlled by the degree of connectivity between host plants during the prior year than by current connectivity. This discrepancy may be due to changes in plant species coverage in a year and/or to the delay of dispersal response of fungi. This study it the first to demonstrate how small-scale host-plant distributions mediate connectivity in microorganisms. The consequences of plant distributions for the permeability of the floristic landscape to fungi dispersal appear to control fungal assemblages, but with possibly different mechanisms for the different fungal groups.