Format: ORAL

Sara Frasca1, Annamaria Alabiso1, Chiara Conte1, Loredana Manfra2, Alice Rotini2, Marlen I. Vasquez3, Eleni Christoforou3, Gidon Winters4, Moran Kaminer4, Luciana Migliore1,5

1 Department of Biology, University of Rome Tor Vergata, 00133, Rome, Italy 2 Institute for Environmental Protection and Research (ISPRA), 00144, Rome, Italy 3 Department of Environmental Science and Technology, Cyprus University of Technology, 3036, Limassol, Cyprus 4 The Dead Sea and Arava Science Center (ADSSC), 8698000, Mount Masada, Israel 5 eCampus University, 22060, Novedrate (CO), Italy

Posidonia oceanica (L) Delile is a threatened endemic seagrass of the Mediterranean Sea. As a Mediterranean Climax community, Posidonia meadows hold high ecological relevance in primary productivity, food web support and nutrient cycling, also providing multiple ecosystem services as biodiversity hotspot, ecosystem engineering or carbon sink. Despite its recognised importance, Posidonia meadows are declining at an accelerating rate by global or local anthropogenic pressures. Like terrestrial plants, P. oceanica host a diverse community of microorganisms which may influence its ecophysiology and health, even regulating the biogeochemical dynamics of entire meadows. Among microorganisms, very little is known about P. oceanica mycobiome. Fungi in terrestrial ecosystems are known to confer benefits to the plant and could play a crucial role in functioning of the seagrass ecosystem, spanning from mutualism to parasitism. We performed a large-scale sampling at 3 localities in the Mediterranean Sea (France; Crete and Cyprus respectively) and a Next Generation Sequencing (NGS) study based on ITS2 and 5.8S rDNA sequence analyses, in order to investigate how the fungal communities’ structure and composition associated with the P. oceanica environmental matrices (seawater column or sediment) and plant compartment (leaves, roots or rhizome) differ according to environmental variability and biometrics or physiological descriptors. A single species dominated the fungal community, Posidoniomyces atricolor, hitherto unknown from other hosts and supposed to be responsible for the putative dark septate endophyte (DSE) colonization pattern found in P. oceanica. Out of P. atricolor, the less dominant taxa showed a strong plant compartment specificity. The consistent occurrence of the DSE suggested a mutualistic relationship as with mycorrhizal fungi in terrestrial plants, representing an integrated approach for the monitoring of the P. oceanica meadows in an even more changing environmental condition.