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Posidonia oceanica retains a large amount of carbon within its belowground recalcitrant structure, the 'matte,' which is characterized by low oxygen availability and biodegradation. Fungi may play a pivotal role in carbon sequestration within the matte, even if little/no information is available. To fill this gap, we profiled fungal communities from the upper and lower layers of alive and dead matte, by using an ITS2-5.8S rDNA metabarcoding approach. The study was conducted in a shallow coastal stretch of the Aegean Sea (Crete). Then, 184 operational taxonomic units were identified, predominantly belonging to Ascomycota, in alive and dead matte. Nevertheless, their composition significantly differed: the host-specific Posidoniomyces atricolor was dominant in alive but not in dead matte, while fast-growing saprotrophs, potentially accelerating the decomposition rate, increased in dead matte. These findings lay the groundwork for future investigations on the possible increase of biodegradation under the changing environmental conditions. [ABSTRACT FROM AUTHOR]

The anchoring and mooring of boats mechanically damage Posidonia oceanica plants; however, no information is available on the effect of this kind of damage on the plant holobiont, i.e., on the associated bacterial and fungal communities. Indeed, bacterial communities are known to change under different plant stress conditions but the dynamics of seagrass-associated fungi remain largely unexplored. We used DNA metabarcoding to profile the bacterial and fungal colonizers of two nearby P. oceanica patches in the Villefranche-sur-Mer bay (France) differing by the amount of exposure to mechanical stress due to boat transit and anchoring. Bacterial communities showed a significant reduction in diversity with an increase in Vibrio sp. in the rhizome and root samples from the impacted site, where the accumulation of dead organic material favors opportunistic heterotrophs. Conversely, fungal communities showed increased diversity in the leaf samples from the impacted site, where a reduction in the dominant P. oceanica host-specific mutualistic endosymbiont, Posidoniomyces atricolor, was found. This change was probably due to the opening up of new colonizable niches for several fungal species. Although this study represents a preliminary assessment of the effect of mechanical stresses on P. oceanica-associated microbial communities, it further supports their putative use as a seagrass descriptor. [ABSTRACT FROM AUTHOR]

Abstract Background The endemic seagrass Posidonia oceanica (L.) Delile colonizes soft bottoms producing highly productive meadows that play a crucial role in coastal ecosystems dynamics. Human activities and natural events are responsible for a widespread meadows regression; to date the identification of "diagnostic" tools to monitor conservation status is a critical issue. In this study the feasibility of a novel tool to evaluate ecological impacts on Posidonia meadows has been tested. Quantification of a putative stress indicator, i.e. phenols content, has been coupled to 2-D electrophoretic protein analysis of rhizome samples. Results The overall expression pattern from Posidonia rhizome was determined using a preliminary proteomic approach, 437 protein spots were characterized by pI and molecular weight. We found that protein expression differs in samples belonging to sites with high or low phenols: 22 unique protein spots are peculiar of "low phenols" and 27 other spots characterize "high phenols" samples. Conclusion Posidonia showed phenols variations within the meadow, that probably reflect the heterogeneity of environmental pressures. In addition, comparison of the 2-D electrophoresis patterns allowed to highlight qualitative protein expression differences in response to these pressures. These differences may account for changes in metabolic/physiological pathways as adaptation to stress. A combined approach, based on phenols content determination and 2-D electrophoresis protein pattern, seems a promising tool to monitor Posidonia meadows health state.