Biogeographic history of a large clade of ectomycorrhizal fungi, the Russulaceae, in the Neotropics and adjacent regions.

The biogeography of neotropical fungi remains poorly understood. Here, we reconstruct the origins and diversification of neotropical lineages in one of the largest clades of ectomycorrhizal fungi in the globally widespread family Russulaceae. We inferred a supertree of 3285 operational taxonomic units, representing worldwide internal transcribed spacer sequences. We reconstructed biogeographic history and diversification and identified lineages in the Neotropics and adjacent Patagonia. The ectomycorrhizal Russulaceae have a tropical African origin. The oldest lineages in tropical South America, most with African sister groups, date to the mid-Eocene, possibly coinciding with a boreotropical migration corridor. There were several transatlantic dispersal events from Africa more recently. Andean and Central American lineages mostly have north-temperate origins and are associated with North Andean uplift and the general north-south biotic interchange across the Panama isthmus, respectively. Patagonian lineages have Australasian affinities. Diversification rates in tropical South America and other tropical areas are lower than in temperate areas. Neotropical Russulaceae have multiple biogeographic origins since the mid-Eocene involving dispersal and co-migration. Discontinuous distributions of host plants may explain low diversification rates of tropical lowland ectomycorrhizal fungi. Deeply diverging neotropical fungal lineages need to be better documented.

Taxonomic, phylogenetic and functional diversity of root-associated fungi in bromeliads: effects of host identity, life forms and nutritional modes.

Bromeliads represent a major component of neotropical forests and encompass a considerable diversity of life forms and nutritional modes. Bromeliads explore highly stressful habitats and root-associated fungi may play a crucial role in this, but the driving factors and variations in root-associated fungi remain largely unknown. We explored root-associated fungal communities in 17 bromeliad species and their variations linked to host identity, life forms and nutritional modes by using ITS1 gene-based high-throughput sequencing and by characterizing fungal functional guilds. We found a dual association of mycorrhizal and nonmycorrhizal fungi. The different species, life forms and nutritional modes among bromeliad hosts had fungal communities that differ in their taxonomic and functional composition. Specifically, roots of epiphytic bromeliads had more endophytic fungi and dark septate endophytes and fewer mycorrhizal fungi than terrestrial bromeliads and lithophytes. Our results contribute to a fundamental knowledge base on different fungal groups in previously undescribed Bromeliaceae. The diverse root-associated fungal communities in bromeliads 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.

Surprising low diversity of the plant pathogen Phytophthora in Amazonian forests.

The genus Phytophthora represents a group of plant pathogens with broad global distribution. The majority of them cause the collar and root-rot of diverse plant species. Little is known about Phytophthora communities in forest ecosystems, especially in the Neotropical forests where natural enemies could maintain the huge plant diversity via negative density dependence. We characterized the diversity of soil-borne Phytophthora communities in the North French Guiana rainforest and investigated how they are structured by host identity and environmental factors. In this little-explored habitat, 250 soil cores were sampled from 10 plots hosting 10 different plant families across three forest environments (Terra Firme, Seasonally Flooded and White Sand). Phytophthora diversity was studied using a baiting approach and metabarcoding (High-Throughput Sequencing) on environmental DNA extracted from both soil samples and baiting-leaves. These three approaches revealed very similar communities, characterized by an unexpected low diversity of Phytophthora species, with the dominance of two cryptic species close to Phytophthora heveae. As expected, the Phytophthora community composition of the French Guiana rainforest was significantly impacted by the host plant family and environment. However, these plant pathogen communities are very small and are dominated by generalist species, questioning their potential roles as drivers of plant diversity in these Amazonian forests.

Fungi of French Guiana gathered in a taxonomic, environmental and molecular dataset.

In Amazonia, the knowledge about Fungi remains patchy and biased towards accessible sites. This is particularly the case in French Guiana where the existing collections have been confined to few coastal localities. Here, we aimed at filling the gaps of knowledge in undersampled areas of this region, particularly focusing on the Basidiomycota. From 2011, we comprehensively collected fruiting-bodies with a stratified and reproducible sampling scheme in 126 plots. Sites of sampling reflected the main forest habitats of French Guiana in terms of soil fertility and topography. The dataset of 5219 specimens gathers 245 genera belonging to 75 families, 642 specimens are barcoded. The dataset is not a checklist as only 27% of the specimens are identified at the species level but 96% are identified at the genus level. We found an extraordinary diversity distributed across forest habitats. The dataset is an unprecedented and original collection of Basidiomycota for the region, making specimens available for taxonomists and ecologists. The database is publicly available in the GBIF repository ( https://doi.org/10.15468/ymvlrp ).

Diversity and Structure of Fungal Communities in Neotropical Rainforest Soils: The Effect of Host Recurrence.

The patterns of the distribution of fungal species and their potential interactions with trees remain understudied in Neotropical rainforests, which harbor more than 16,000 tree species, mostly dominated by endomycorrhizal trees. Our hypothesis was that tree species shape the non-mycorrhizal fungal assemblages in soil and litter and that the diversity of fungal communities in these two compartments is partly dependent on the coverage of trees in the Neotropical rainforest. In French Guiana, a long-term plantation and a natural forest were selected to test this hypothesis. Fungal ITS1 regions were sequenced from soil and litter samples from within the vicinity of tree species. A broad range of fungal taxa was found, with 42 orders and 14 classes. Significant spatial heterogeneity in the fungal communities was found without strong variation in the species richness and evenness among the tree plots. However, tree species shaped the fungal assemblages in the soil and litter, explaining up to 18 % of the variation among the communities in the natural forest. These results demonstrate that vegetation cover has an important effect on the structure of fungal assemblages inhabiting the soil and litter in Amazonian forests, illustrating the relative impact of deterministic processes on fungal community structures in these highly diverse ecosystems.

Contrasting responses to mycorrhizal inoculation and phosphorus availability in seedlings of two tropical rainforest tree species.

• This work aimed at understanding the role of mycorrhizal status in phosphorus efficiency of tree seedlings in the tropical rainforest of French Guyana. • Mycorrhizal colonization, growth, phosphorus content, net photosynthesis and root respiration were determined on three occasions during a 9-month growth period for seedlings of two co-occurring species (Dicorynia guianensis and Eperua falcata) grown at three soil phosphorus concentrations, with or without inoculation with arbuscular mycorrhizas. • Seedlings of both species were unable to absorb phosphorus in the absence of mycorrhizal association. Mycorrhizal seedlings exhibited coils that are specific of Paris-type mycorrhizae. Both species benefited from the mycorrhizal symbiosis in terms of phosphorus acquisition but the growth of E. falcata seedlings was unresponsive to this mycorrhizal improvement of phosphorus status, probably because of the combination of high seed mass and P reserves, with low growth rate. • The two species belong to two different functional groups regarding phosphorus acquisition, D. guianensis being an obligate mycotrophic species.