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

International audienceIn 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 indersampled 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)

Do mycorrhizas improve tropical tree seedling performance under water stress and low light conditions ? A case study with dicorynia guianensis (Caesalpiniaceae)

We tested the response of seedlings of Dicorynia guianensis, a major timber tree species of French Guiana, to mycorrhizal symbiosis and water limitation in a semi-controlled experiment under natural light conditions. Under well-watered conditions, mycorrhizal colonization resulted in an increase of net photosynthesis, growth and phosphorus uptake. When submitted to water stress, no growth reduction of mycorrhizal seedlings was observed. Mycorrhizal seedlings were more sensitive to drought than non-mycorrhizal ones in terms of carbon assimilation, but not with regard to stomatal closure. In contrast to previous studies on temperate tree seedlings, this result precludes a mycorrhizal effect on the hydraulic properties of this species. Furthermore, our results suggest that below a specific threshold of soil moisture, carbon assimilation of D. guianensis seedlings was decreased by the mycorrhizal symbiosis. This is probably related to the competition between the plant and its host fungus for carbon allocation under low light intensity, even though it did not seem to have a significant effect on mortality in our experiment

Arbuscular mycorrhizas in dicorynia guianensis and eperua falcata trees from primary tropical rain forest of French Guiana

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How significant are endophytic fungi in bromeliad seeds and seedlings?: Effects on germination, survival and performance of two epiphytic plant species

International audienceIn bromeliads, nothing is known about the associations fungi form with seeds and seedling roots. We investigated whether fungal associations occur in the seeds and seedling roots of two epiphytic Aechmea species, and we explored whether substrate and fungal associations contribute to seed germination, and seedling survival and performance after the first month of growth. We found a total of 21 genera and 77 species of endophytic fungi in the seeds and seedlings for both Aechmea species by Illumina MiSeq sequencing. The fungal associations in seeds were found in the majority of corresponding seedlings, suggesting that fungi are transmitted vertically. Substrate quality modulated the germination and growth of seedlings, and beneficial endophytic fungi were not particularly crucial for germination but contributed positively to survival and growth. Overall, this study provides the first evidence of an endophytic fungal community in both the seeds and seedlings of two epiphytic bromeliads species that subsequently benefit plant growth

Mycorrhizal symbiosis and inorganic nutrition

En Guyane française où les sols sont généralement acides et pauvres en éléments minéraux, la forêt est caractérisée par sa plurispécificité. Une approche de type écologique a montré, dans les racines des principales espèces forestières, la dominance d'endomycorhizes à structure intracellulaire particulière : des hyphes de type Paris, spiralé. Leur rôle dans l'acquisition du phosphore a été étudié expérimentalement chez deux Césalpiniacées. Les semis d'Angélique, Dicorynia guianensis Amshoff, sont très dépendants, pour leur croissance et leur teneur en phosphore, des mycorhizes à mycélium spiralé ; ce type de mycélium représente plus de 90 % de la colonisation fongique. Par contre, les semis de Wapa (Eperua falcata Aublet) forment également des mycorhizes mais ces dernières améliorent le statut phosphaté et sont sans effet sur la croissance de cette espèce. Ces résultats contribuent à la compréhension du rôle des symbioses endomycorhiziennes dans le processus de régénération naturelle et ouvrent des perspectives de recherche quant à leur intervention éventuelle dans le maintien de la diversité forestière

Effects of endomycorrhizal development and light regimes on the growth of Dicorynia guianensis Amshoff seedlings (experimental approach)

Effet des mycorhizes et de la lumière sur la croissance des semis de Dicorynia guianensis Amshoff, une césalpiniacée de la forêt tropicale humide de Guyane française. Des semis de D. guianensis ont été cultivés en pots sur un sol désinfecté, inoculé ou non avec du sol forestier, dans des serres tunnels sous trois régimes lumineux (1 %, 14 %, 50 % du plein découvert). Des paramètres de croissance des plants et la colonisation endomycorhizienne des racines ont été mesurés au bout de 50 semaines. Les semis soumis à 1 % d'éclairement et croissant sur les deux types de sol ne présentaient aucune différence significative pour aucun des caractères mesurés, bien qu'un taux élevé de mycorhization aie été noté chez les plants sur sol inoculé. En éclairement partiel, 14 et 50 %, les performances de croissance des semis étaient positivement reliées au taux d'infection mycorhizienne. L'optimum de croissance était obtenu pour l'intensité lumineuse moyenne (14 %), montrant ainsi une meilleure efficacité des mycorhizes.The influence of mycorrhizal infection rate and light environment on growth traits was examined for 50-week-old Dicorynia guianensis Amshoff tree seedlings. The seedlings were grown on two soil substrates (control and inoculated) in shade tunnels under three relative light levels (50%, 14% and 1% of full sunshine). For seedlings growing under 1% of full sunlight no significant differences between control and inoculated plants were observed in plant traits though a high rate of endomycorrhizal infection was recorded. In partial shaded sunlight, 14% and 50%, the rate of mycorrhizal infection was positively related to the growth performances of seedlings. The optimal growth was obtained under 14% of full sunlight, showing a greater efficiency of the mycorrhizas

Biotic drivers of root-associated fungal community in neotropical bromeliads

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