Uncovering leaf and root microbiomes of mangrove trees in French Guiana

Microorganisms are now widely acknowledged as essential contributors to the health and resilience of coastal environments. Yet, mangrove ecosystems, despite offering numerous ecological and economic services, remain relatively overlooked in microbial research. In this study, we examined the bacteriome of the rhizosphere and the phyllosphere of two mangrove tree species: Avicennia germinans and Rhizophora mangle. Both species were sampled along the banks of the Sinnamary estuary in French Guiana. Our results revealed notable differences in microbiome composition between the two organs and between the two tree species. On average, only 0.3% of ASVs were shared between the leaves and roots and 2.2% between A. germinans and R. mangle. The taxonomic differences were characterized mainly by the significant presence of Rhodothermia and Bacteroidia in the leaves and Cyanobacteria and Planctomycetia in the roots. Furthermore, our results showed that the root microbiome of both species was only weakly influenced by the surrounding water and sediment, with an average of less than 0.7% of ASVs shared. Finally, our study indicates a strong specificity in the bacterial communities of both the phyllosphere and rhizosphere and also raises questions regarding the near absence of Gammaproteobacteria in both the leaves and roots, which remain to be elucidated.