CE02 - Terre vivante

Epiphytism as a Fungal Ecosystem conquered by Vascular Plants – EPIFUN

EPIFUN

Epiphytism as a fungal ecosystem conquered by vascular plants

Mycorrhizal symbioses revisited in tropical epiphytic environments

EPIFUN investigates the diversity and structure of fungal communities (Fungi) in tropical epiphytic environments, and the symbioses that are formed with the roots of epiphytic plants (orchids, ferns, lycophytes, etc.). We seek to understand the spatial structure of different functional groups of fungi on the bark, near or far from the roots of epiphytic plants; the horizontal distribution of mycorrhizal fungal communities among different host tree species on which epiphytic plants establish; whether the distribution of symbiotic fungi constrains that of epiphytic plants to certain hosts (host preference); the vertical stratification of total and mycorrhizal fungal communities on the tree, from soil to canopy; whether segregation or sharing of symbiotic fungi prevails in epiphytic plant communities that coexist on branches or trunks; whether some epiphytic plants, adult or juvenile, acquire organic carbon from photosynthesis from other epiphytes, or from the host tree itself, via the network of symbiotic associations.

EPIFUN develops and uses high-throughput sequencing techniques for total fungal communities and mycorrhizal communities more specifically. These techniques are based on metabarcoding of the ITS-2 region in Asco- and Basidiomycetes, or of an 18S variable region in endomycorrhizal fungi (Glomeromycotina). We have a wide range of oligonucleotide primers to more or less specifically amplify certain fungal taxa, and to process them in multiplex. In addition to sequencing techniques, we collect the roots of tropical plants in order to observe and describe these new identified fungal symbioses. Finally, experimental studies on the symbiotic germination of epiphytic plants on trees, or on the transfer of labeled elements via the common mycorrhizal network, complete our research.

During the first 18 months of the project, we were able to sample and analyze the fungal communities on several host tree species in the Mare-longue forest in Réunion, in order to study the mycorrhizal networks in these habitats, and the role of mycorrhizal fungal communities in the host preference of some epiphytic orchids. We are also collaborating with national and international researchers to study the ecology of vascular epiphytes, and their interactions with microbial communities on the tree, in other tropical regions of the world. We recently demonstrated the spatial structure of the different functional groups of fungi (symbiotics, pathogens, etc.) found on the bark, and the rhizosphere effect in certain epiphytic orchids of the Brazilian Atlantic forest.

When we have analysed the data on the mycorrhizal networks formed between plants and epiphytic fungi in rain forest, we will carry out isotopic labelling experiments in order to test whether organic carbon transfers operate between epiphytic plants via the common mycorrhizal network, in particular in the case of orchids that develop a fungal symbiosis as soon as the seeds germinate.

Petrolli, Remi, Conrado Augusto Vieira, Marcin Jakalski, Melissa F. Bocayuva, Clement Valle, Everaldo da Silva Cruz, Marc-André Selosse, Florent Martos, and Maria Catarina M. Kasuya. «A fine-scale spatial analysis of fungal communities on tropical tree bark unveils the epiphytic rhizosphere in orchids.« New Phytologist (2021). doi.org/10.1111/nph.17459

The high abundance and diversity of plants living as epiphytes, on the nutrient-poor surface of other plants, such as e.g. many orchids and other members of the pineapple family (Bromeliaceae), have long fascinated tropical ecologists. Yet, the reasons explaining the success of this lifestyle and the high diversity of epiphyte species, even on a single tree, remain poorly understood. One possible explanation potentially lies in the facilitating role of the plants microbiota, whether that of epiphytic plants or of their living support, in the germination, growth and coexistence of epiphytic plants. The project EPIFUN tackles this question by focusing on the fungi colonizing the roots of vascular epiphytes, including the mutualistic mycorrhizal fungi.
More specifically, EPIFUN addresses five main scientific objectives: (i) to determine whether the fine-scale spatial distribution of fungal communities on bark surface co-varies with the presence of epiphytes; (ii) to assess whether root-associated fungi are specific to their epiphytic host or whether they exhibit a “horizontal structure”, i.e. depend on the identity of the supporting trees, or a “vertical structure”, caused by local environmental gradients from the roots to the top of tree crowns; (iii) to experimentally test to which extent fungi constrain the distribution of epiphytes on certain phorophytes, particularly when a specific fungal symbiont is required for germination and growth of the epiphytic plant; (iv) to assess if segregation or sharing of root endophytic fungi drives the coexistence of epiphytic species on trees, and if this pattern is consistent along a gradient of stress for epiphytes; (v) to determine to which extent epiphytes gain carbon by fungal pathway, from neighboring epiphytes and from the supporting tree itself.
EPIFUN is intended to promote the development of a new research team in its host institution, i.e., Institut de Systématique Evolution Biodiversité (UMR7205), working on the new promising topic of plant-microbiota interactions in tropical ecosystems, and approaching the supports for epiphytic plants as living communities rather than mere physical supports. For this purpose, the project brings together young and mid-career scientists, including experts on: (i) taxonomy, systematics and ecology of tropical epiphytes, especially orchids, lycophytes and ferns, to carry out field studies in the tropical areas covered by EPIFUN, i.e. La Réunion and French Guiana; (ii) environmental genomics and fungal metabarcoding precisely, to achieve the identification of fungal communities from the roots and from the epiphytic substrata directly; (iii) bioinformatics, biostatistics, and community ecology to analyse the data; (iv) experimental approach (including isotopic labelling) to assess functional aspects of the plant-fungal interactions.
As a multidisciplinary project in an overlooked field of research, EPIFUN is expected to have an impact among the scientific audience covering environmental genomics, tropical ecology, fungal ecology, plant ecology and physiology, and plant and fungal systematics. This project is not only committed to research but also to education and dissemination of scientific knowledge. First, it is meant to be attractive for new PhD students and post-doctoral researchers. Last but not least, it is meant to be attractive for the general public by tacking advantage of the attendance levels of its host institution, the Muséum national d’Histoire naturelle (MNHN), and by organizing outreach in the French regions where sampling and experiments will take place.

Project coordination

Florent Martos (Institut de Systématique, Evolution, Biodiversité)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

2AD Acquisition et Analyse de Données pour l'histoire naturelle
IBENS Institut de Biologie de l'Ecole Normale Supérieure
ISYEB Institut de Systématique, Evolution, Biodiversité

Help of the ANR 288,144 euros
Beginning and duration of the scientific project: December 2019 - 48 Months

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