Résumé
Interactions between fungi and plant roots have played a key role in the diversification and adaptation of plants to many environmental conditions and are of primary importance given the sessile lifestyle of plants. Root-associated fungi may be crucial for epiphytic (i.e. plants that grow on the surface of another plant) and lithophytic plants (i.e. plants that grow on rocks) to cope with highly stressful habitats (e.g. wide temperature ranges, limited water and nutrient availability). Besides abiotic factors, biotic factors such as host phylogeny or the interactions between co-existing species were suggested to affect the distribution patterns of root-associated fungi. In bromeliads, most of the root-associated fungal endophytes remain undescribed as well as the drivers that affect their interactions with the plants. We explored root-associated fungal communities in bromeliad species and their variations linked to plant ecology, ontogeny, and ant-plant interactions, by using ITS1 gene-based high-throughput sequencing and by characterizing fungal functional guilds. Overall, we found a dual association of mycorrhizal and non-mycorrhizal fungi. The ecology of the plant (epiphytic, lithophytic and terrestrial forms) among bromeliad species shaped both the taxonomic and the functional composition of fungal communities. Specifically, roots of epiphytic bromeliads had more endophytic fungi and dark septate endophytes and fewer mycorrhizal fungi than terrestrial and lithophytic bromeliads. In addition, we underlined changes in root-associated fungal communities linked to the ontogenic stage of bromeliads, with a prominence of mycorrhizal and lower dark septate endophyte fungi in the adults, as compared to juveniles. Finally, we evidenced that root-fungal community composition can be mediated by cross-kingdom interactions. Indeed, we found that the identity of the mutualistic ant species in ant-bromeliad interactions had a significant influence on the root-associated fungal diversity and community composition. Our results contribute to a fundamental knowledge base on different fungal groups in previously undescribed bromeliad plants. We evidenced that multiple biotic drivers had strong effects on root-associated fungal community that may enhance plant fitness in both stressful and nutrient-poor environments and may give more flexibility to the plants to adapt to changing environmental conditions.