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International audience; In the French Alps, dendrochronologists are studying timbers used in mountain (rural buildings, mining structures) for about twenty years. 1730 Larch, Spruce Fir, Scots pine and oaks timbers (cores and sections) were tree ring dated at more than a hundred buildings located between 790 and 2356 m a.s.l. Several felling dates clusters were identified, from the 11th c. to the 20th c. Except during the second half of the 14th century, trees were felled during all times, which testifies to an almost continuous activity of buildings’ maintenance, repairs and transformation. The evolution of felled timbers age and diameter over the last ten centuries reveals the forest resources management by rural societies. We show an increase in the age of the trees felled from the 11th to the beginning of the 14th century, up to ca. 250 years old. From the end of the 14th to the beginning of the 20th century, the trees were felled at a median age of 100 years. Moreover, diameters of the used trees used are more or less constant over time (around 20-25 centimeters), because these dimensions are perfectly suited for the (mostly studied) structural elements of mountain constructions.As diameter has remained constant whereas the age of the felled trees has changed, growth conditions have therefore improved over the ten centuries studied. A climatic explanation is difficult to retain for this medieval-modern period discrepancy. Rather, anthropic explanation, impacting silvicultural practices and favoring growth would be a more relevant hypothesis.

Leaf-inhabiting fungal and bacterial endophytes are at their most diverse in tropical rainforest plant hosts, with some influencing host plant fitness as either symbionts or pathogens. Endophyte activity and community composition is thought to depend on competition amongst co-occurring species for resources. Here, we reveal the strength of competitive interactions between endophytes by combining e-DNA metabarcoding to characterize the community with culturing assays to ascertain their potential activity. The endophyte community associated with the understory palm Astrocaryum sciophilum was determined by extracting eDNA from 120 leaflets of eight plants located in a lowland rainforest in French Guiana. This revealed 516 fungal and 606 bacterial Operational Taxonomic Units (OTUs). Co-occurrence analysis of the most abundant OTUs revealed that direct fungal-fungal interactions were overall more negative than bacterial-bacterial interactions. This was confirmed by C-score calculations for the whole endophyte community, revealing significantly greater levels of species segregation for fungi but not bacteria when compared with simulated random communities. Following the culturing of 131 fungal, and 66 bacterial Astrocaryum endophytes collected from the same leaves, Minimal Inhibitory Concentrations of ethyl acetate culture extracts were evaluated against the fungus Trichophyton rubrum and the bacterium Staphylococcus aureus. Overall, a minority of extracts demonstrated antipathogen activity, with greater antifungal activity expression for both fungi and bacteria when compared with antibacterial activity. In order to explore whether this activity translated into competitive structuring of the community, a BLAST was conducted to match metabarcoding sequences with Sanger derived culture sequences. This demonstrated that cultures displaying antipathogen activity were significantly more likely to co-occur with fungi if they were bacteria, and bacteria if they were fungi. Nevertheless, overall correlation values averaged around zero. These results indicate that for Astrocaryum palms, fungal endophytes are likely to play a greater role in determining colonization success of subsequent endophytes whether these be fungal or bacterial, but that overall endophyte communities do not display strong patterns of community structuring through competition. Endophyte communities are thus likely to reach relative stasis in mature leaves, where the diverse community of fungi and bacteria amongst other factors prevent the subsequent establishment of pathogens.

Rapport scientifique et financier du projet FORETEXIL : Les vieilles FORETs des Maramureș (Carpates orientales) face à l’EXploitation forestière Intensive : plan d'urgence pour une étude globale en vue de leur préservation et gestion durable., Scientific and financial report of FORETEXIL project (OASIC funds).