What happens with bacteria in the roots affects what happens with fungi in the leaves

The impact of plant-bacteria symbioses in roots on plant-fungus interactions in distant tissues, such as leaves, remains a significant knowledge gap, particularly for tropical ecosystems. We employed amplicon metabarcoding of ITS2 sequences to analyze the endophytic fungal communities of eight tropical Fabaceae tree species to determine variations according to the hosts root nodulation capacity and the hosts subfamily affiliation. Nitrogen-fixing bacteria in root nodules significantly impacted the diversity and composition of fungal endophytes, while subfamily affiliation had a less pronounced effect. In non-nodulating plants, leaves harbored a much larger diversity of fungi, with 25 fungal classes and 72 orders compared to 17 classes and 45 orders in nodulating plants. Notably, 40% of the orders were unique to non-nodulating plants, whereas only 5% were exclusive to nodulating species. This pattern was further reflected in the number of fungal ASVs, with non-nodulating plants averaging 130.5 compared to 42.7 in nodulating plants. Similarly, Shannon diversity was significantly higher in non-nodulating plants. This study demonstrates that interactions between Fabaceae plants and nitrogen-fixing root bacteria significantly influence the richness and diversity of the fungal community present in leaves. Our findings contribute valuable insights into the complex interplay between plants and microorganisms, particularly in the context of tropical Fabaceae tree species and their endophytic fungi.