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A microwave‐based process to control invasive species (seeds and adult stages) in the field prior to plant community restoration is currently under development. We investigated the effect of four microwave treatment pairings of Power × Duration (2kW4min, 4kW2min, 2kW8min, and 4kW4min) on seedling emergence of (1) an abandoned field seed bank used as a model for various plant species and (2) seeds of three species invasive in Europe: Datura stramonium (Jimson weed), Reynoutria × bohemica (Bohemian knotweed), and Solidago gigantea (Giant goldenrod). In addition, we assessed whether nontreated seeds of these three invasive species could germinate on microwave‐treated soils. As microwave soil heating usually leads to nonhomogeneous temperatures within a sample, we also assessed whether the position of seeds in the soil during microwave treatment (center vs. edges) impacted seedling emergence. Results show that the most intensive microwave treatments (2kW8min and 4kW4min), enabling the soil to reach 85°C, are highly effective in inhibiting seedling emergence of invasive species and the seed bank. The 2kW8min treatment, combining lowest power and longest exposure, is the most effective, reducing seed bank seedling emergence by 98% compared to control. The results also reveal a species‐specific response to heat, and lower microwave effectiveness on seeds located at the soil surface, which may explain the incomplete effectiveness of intensive treatments. Our results also suggest that prior microwave soil treatment does not prevent a considerable proportion of newly arrived invasive species seeds from germinating, suggesting that this method should be followed by restoration of native plant cover.

Questions The effect of dewatering on aquatic plant communities may vary with sediment properties, such as particle size and organic matter content, as both control water retention in the sediment during dewatering. No study has tested how sediment type affects the short-term response of plant communities to dewatering. We hypothesized that for the same dewatering event: (1) organic, silt and coarse sediments rank along a gradient of water deficit, with which community resistance and resilience decrease; (2) species survival during the event depend on their known ecological affinity for water; and (3) a peak in species richness associated with an intermediate water deficit occurs in silty habitats. Location Riverine wetlands in the floodplain of the Ain River, France. Methods Eighteen sampling units were defined, set over three sediment types: gravel-dominated coarse sediment, silt and organic matter-dominated sediment. For each sediment type, three sampling units were permanently aquatic, and three sampling units underwent summer dewatering. A survey of species cover was conducted in each sampling unit at four times: before summer dewatering, at the beginning of the event, at the end of the event and 2 months after rewetting. Community resistance and resilience were assessed, as were changes over time in the proportions of species according their water affinity (hydrophytes, amphiphytes and helophytes, documented from the floras), and the effect of dewatering on species renewal and richness. Results The sediment type affected aquatic plant community resistance and resilience, with increasing disturbance intensity for silty, followed by coarse compared with organic sediment. Organic sediment retained water efficiently during dewatering, supporting high community resistance, with the maintenance of amphiphytes and more tolerant hydrophytes. On silty sediment, disturbance was sufficiently high to cause the disappearance of hydrophyte vegetative parts, but propagules rapidly sprouted after rewetting, suggesting their preservation in the sediment and enabling good community resilience. On coarse sediment, a decrease in resident amphiphyte abundance, together with helophyte colonization and maintenance after rewetting were observed. Coarse sediment is not favourable to propagule survival, explaining the low community resilience. Contrary to our hypothesis, a linear positive relationship between disturbance intensity and species richness was observed after dewatering. Conclusion The present study demonstrates that a simple description of sediment type allows prediction of dewatering impact on aquatic plant communities: organic, silt and coarse sediments were ranked along a gradient of water deficit, along which resistance and resilience decreased.

Intermittent rivers and ephemeral streams (IRES) support highly biodiverse primary producers, including algae, cyanobacteria, and aquatic and riparian plants. All these groups share common traits to cope with a harsh environment whose water table varies and where desiccation is common. Traits include morphological characteristics, life cycle adaptations, and physiological mechanisms to contend with hydric stress and increased water temperatures. Despite these environmental challenges, primary producers play ubiquitous roles in the fluxes of energy and material in IRES. They are the basis for ecosystem metabolism, expressed as episodic pulses of production that occur immediately following rewetting, when their abundant output of high-quality organic matter is critical for supporting consumers both in-stream and in the neighboring terrestrial system.

International audience; Slash-and-burn cultivation is a major cause of deforestation in Madagascar, and abandonment leads to the secondary vegetation dynamics, i.e. colonization by herbaceous vegetation, shrubs and trees. The study was conducted in south-eastern Madagascar in a steep transition zone along an altitudinal and a sharp precipitation gradient between a high altitude rainforest and a lowland dry tropical forest. The restoration of gaps created by abandoned fields in this narrow, winding corridor could be essential to maintain connectivity between two areas (areas 1 and 2) of Andohahela National Park. Prior to imple- menting restoration, baseline ecological information is needed on the reference ecosystem and vegetation resilience must be studied to identify restoration needs. This study aims to (1) assess whether cultiva- tion practices (irrigated rice vs. cassava, maize and sweet potato) influence vegetation dynamics after abandonment; (2) study vegetation dynamics and soils over time since abandonment, and (3) compare secondary forest vegetation and soils with those of mature forest patches. Surveys of vegetation and soil were conducted in 26 secondary forest patches abandoned from 3 to >25 years (synchronic approach) and in 19 adjacent mature forest patches (controls). No relationship between age of abandonment and vege- tation species richness, composition or structure was found, but clear differences were detected between secondary and mature forest patches. Secondary forests are not colonized by species from mature forests, but instead their vegetation dynamics appear to lead to the establishment of thorny thickets dominated by Mimosa delicatula, which is absent from the mature forest.

International audience; Due to global change, many wetlands experience water level decreases and changes in their hydrological func- tioning, modifying their physico-chemical characteristics. Riverine wetlands are particularly complex within this frame- work because they are supplied by different water sources. This study assessed how long-term water level decreases in riverine wetlands relate to changes in their physico-chemical characteristics (temperature, oxygen, pH, conductivity and nutrient contents: nitrate, ammonium and phosphate). We hy- pothesized that 1) water level decreases have no effect on water nutrient contents because of the high water renewal by groundwater supplies, which may leach nutrients released from the sediment after the dewatering phase, and 2) the physico-chemical characteristics of the water would become increasingly similar to those of hillslope groundwater due to the increase in their water supplies in wetlands. We compared the surface water physico-chemical characteristics of nine riv- erine wetlands with contrasting water level decreases between 1993 and 2011. No increase in water nutrient contents oc- curred. However, depending on the wetland considered, the physico-chemical changes suggested either 1) increased con- nectivity with hillslope groundwater, 2) a lower rate of water renewal in wetlands or 3) increased river water supplies, po- tentially related to river lateral migration toward wetlands.

International audience; Genetic variability is a key component of biodiversity. Therefore, the health of populations that colonise restored ecosystems depends on maintaining a level of genetic diversity similar to what is found in unre- stored and healthy populations. Wetland restoration occurs frequently, but genetic monitoring rarely considers the genetic variability of species that grow spontaneously in restored ecosystems as a marker of overall ecological restoration success. In this study, the temporal dynamics of genetic variability in an aquatic pioneer plant species, Berula erecta (Hudson) Coville (Apiaceae), were assessed based on an anal- ysis of 12 different microsatellite markers. We hypothesised that vegetative propagation was enhanced by restoration and consequently tended to decrease clonal richness and to stabilise genetic diversity. Several genetic and genotypic indices were surveyed over five years in three restored and two reference sites. An assessment of the breeding system in this population suggested that B. erecta was an ISR (initial seedling recruitment) species; for this type of species, disturbances caused by dewatering permitted an increase in the level of genetic diversity. The results suggested that there were no temporal changes in genetic diversity at any of the studied sites over the time scale of the study, despite strong changes in population sizes that were induced by restoration processes. Clonal richness tended to decrease over time, although not significantly. This study demonstrated that restored populations of clonal species maintained their genetic variability over time and that they might even display greater diversity than unrestored populations. This study also underscored the importance of monitoring the genetic diversity of species in restoration projects to maintain biodiversity.

International audience; Temporary dewatering constitutes a drastic change in conditions for aquatic vegetation. Species’ sustained performance under these conditions relies partly on their ability to produce a terrestrial phenotype. Such adaptations may include the development of self-supporting aboveground organs with higher dry matter content enabling plants to withstand gravity and smaller leaves with thicker cuticle to reduce evapotranspiration, leading to lower specific leaf area, higher leaf-construction costs and consequently higher leaf life span. The ability of aquatic plant species to produce a terrestrial-adapted phe- notype may differ according to growth form and evolutionary history. The objectives of this study were to (1) measure the effects of dewatering on aquatic plant performance, (2) determine how growth form and phylogenetic position affect performance, and (3) relate plant performance to plasticity. To meet these objectives, we experimentally studied aquatic plant responses to dewatering by measuring survival, growth, and a set of traits describing the morphology and leaf-resource economy of eight aquatic plant species with contrasting phylogeny and growth forms. The ability of aquatic plants to withstand dewatering differed according to phylogeny but not to growth form. The eudicots presented high survival and similar growth rates under terrestrial compared to aquatic conditions, while monocots generally did not survive dewatering. These species produced phenotypic adjustments, such as denser aboveground organs and leaf plasticity, which can explain the maintenance of similar growth rates under terrestrial conditions. The relatively strong plasticity and performance of eudicots in terrestrial habitats suggests that their optimal niche is the interface between aquatic and terrestrial ecosystems.