Questions: Giving a time advance to restored native plant species has recently been considered a promising way to improve their persistence and reduce invasion success (i.e. through priority effects). However, little is known about the influence of the elapsed time between seeding and invasion and its interaction with other characteristics such as species composition and density, despite the fact that it could substantially help developing effective management strategies.Methods: In a pot experiment, we simulated invasion by three major invasive species (Ambrosia artemisiifolia, Bothriochloa barbinodis, and Cortaderia selloana) in soil covered with recipient communities differing in species composition (one, three or nine species), density (700 or 2,778 seeds/m 2 ), and time advance (established one or five months previously). We assessed early invasion success by measuring seedling emergence and survival over six months.Results: Early invasion success was mainly explained by recipient community's time advance and composition (or their interaction), while density had limited influence. Polycultures (three or nine species) showed generally greater invasion resistance, most likely due to high aboveground biomass essentially produced by two species. Species composition interacted with time advance in two ways: (1) Bothriochloa barbinodis seedling emergence was impacted by composition only in communities having five months of advance, suggesting that the contribution of species composition to invasion resistance varies according to the age of the community, and (2) Ambrosia artemisiifolia and Cortaderia selloana survival was affected by time advance in polycultures only, which produced much more biomass than monocultures, implying that a greater head start provides a competitive advantage only if it allows a sufficient increase in biomass production. Conclusions:Implementing revegetation as soon as site clearance work is over, as well as establishing productive native species may help reduce invasion success. How much of an advantage recipient community time advance represents depends on biomass production.

Mediterranean wetlands are critical strongholds for biodiversity and the provision of ecosystem functions and services; yet, they are being severely degraded by a number of socio-economic drivers and pressures, including climate change. Moreover, we still lack comprehensive understanding of the extent to which biodiversity loss in Mediterranean wetlands will accelerate change in ecosystem processes. Here, we evaluate how changes in biodiversity can alter the ecosystem of the Camargue (southern France). We collected data on species presence/absence, trends and abundance over a 40-year period by combining observations from the scholarly literature with insights derived from expert knowledge. In total, we gathered more than 1500 estimates of presence/absence, over 1400 estimates of species abundance, and about 1400 estimates of species trends for eight taxonomic groups, i.e. amphibians, reptiles, breeding birds, fish, mammals, dragonflies (odonates), orthopterans and vascular plants. Furthermore, we used information on recently arrived species and invasive species to identify compositional changes across multiple taxa. Complementing targeted literature searches with expert knowledge allowed filling important gaps regarding the status and trends of biodiversity in the Camargue. Species trend data revealed sharp population declines in amphibians, odonates and orthopterans, while birds and plants experienced an average increase in abundance between the 1970s and the 2010s. The general increasing trends of novel and invasive species is suggested as an explanation for the changing abundance of birds and plants. While the observed declines in certain taxa reflect the relative failure of the protection measures established in the Camargue, the increasing exposure to novel and invasive species reveal major changes in the community structure of the different taxonomic groups. This study is the first attempt to assess changes in biodiversity in the Camargue using an expert knowledge approach, and can help manage the uncertainties and complexities associated with rapid social-ecological change in other Mediterranean wetlands.

Nanoviruses are multi-component plant-infecting single-stranded DNA viruses. Using a viral metagenomics-informed approach, a new nanovirus and two associated alphasatellite molecules have been identified in an uncultivated asymptomatic Vicia cracca plant in the Rhône region of France. This novel nanovirus genome includes eight genomic components (named DNA-R, DNA-S, DNA-M, DNA-C, DNA-N, DNA-U1, DNA-U2 and DNA-U4) and, across all components, shares < 66% pairwise sequence identity with other nanovirus genomes. The two associated alphasatellites share 62% identity with each other and < 81% identity will all other nanovirus-associated alphasatellites.

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