International audienceHow weed communities assemble represents one the key issues of weed science. For a decade, functional approaches have been applied to investigate the processes that govern weed community assembly. In most previous studies, trait values have been generally averaged over multiple populations and habitats. Consequently, conspecifics display similar trait values while neglecting the considerable influence of intraspecific variability to detect changes in functional diversity in response to environmental drivers. However, this influence has been shown to be critical, especially, at local scales. Here, we studied changes in weed functional diversity at the field scale in four crop sequences. We focused on intra- and interspecific variability of four key functional traits involved in response to resource acquisition processes, the latter being modified by climate, management and competition. The relative influence of intra- and interspecific variability among the crop sequence types was highlighted using a diversity partitioning approach. It provides evidence for substantial amount of intraspecific variability in the weed community and underlines its essential role in response to fine-scale environmental drivers. In addition, we investigated the response of the three most abundant species to competition with the crop, the growing season and the crop sequence type. We highlighted that these species showed a wide range of combinations of trait values, suggesting the co-existence of several successful strategies. Based on these results, we emphasise that neglecting intraspecific variability can lead to substantial underestimations of the functional weed response to management and crop-weed competition at the field scale
Grassland management affects ecosystem services such as the conservation of C stocks. The aim of this study was to analyze the relation between vegetation production and soil C stocks for a set of seven temperate grasslands of various productivity levels. We estimated vegetation production directly through measurements of aboveground biomass (>5 cm), stubble and root biomass, and indirectly via plant community functioning. Soil C stocks were measured for bulk soil (organic C, SOC) and hot-water-extractable C (HWC) of topsoil. Plant community functioning was characterized by community-weighted mean (CWM) traits and functional diversity index. Results show a negative relation between biomass production and SOCstock. The tradeoff between productivity and SOCstock could be linked to plant community functioning and particularly Leaf Dry Matter content (LDMCCWM) which appeared to be the most relevant descriptor of plant community functioning. High SOCstock could be associated to low productivity, conservative strategy (high LDMCCWM), low soil labile C content and grassland age. Our results show a strong direct effect of management and grassland age on plant community, which in turn affects plant tissue quality and subsequent organic matter mineralization. Old permanent grasslands appeared less productive but represent an occasion for C storage and thus global change mitigation.
decline thus amounted to 85%. However, there were considerable regional differences: The decline was as high as 98% in the northern and central Alps but only about 50% in France, where strategies of flood mitigation that allowed for wide river beds proved to be favourable to the conservation of Typha minima.
La petite massette (Typha minima Hoppe) est sujette à une raréfaction dans toute l'Europe. Dans ce contexte, la connaissance précise de sa niche écologique apparaît cruciale pour conduire à bien des opérations conservatoires (renforcement et réintroduction de populations, restauration de cours d'eau). Cette étude a pour objectif principal d'identifier les conditions écologiques (pédologie, hydrologie et espèces compagnes) favorables au développement de cette espèce. Elle s'appuie sur l'analyse de dix stations naturelles situées le long de trois rivières des Alpes nord-occidentales (Arc, Arve et Giffre). Les résultats de ces observations font état de la présence de la petite massette au sein de deux associations différentes, au cortège végétal composite, associant des espèces rudé-rales, prairiales et alluviales. Ils confirment que l'humidité et la nature carbonatée et sablo-limoneuse du substrat favorisent l'espèce. Ils identifient par ailleurs la mise en place d'une succession végétale différente sur les stations submontagnarde et planitiaire. Enfin, ils suggèrent de reconsidérer le positionnement synsystématique de l'association à petite massette et prêle panachée (EquisetoTyphetum minimae) au sein d'un syntaxon morainique et alluvial, l'Epilobion fleischeri, et de s'appuyer sur certaines espèces compagnes telles Salix triandra ou Calamagrostis pseudophragmites pour identifier des sites adaptés à d'éventuels projets de réintroduction de cette espèce.Mots clés Phytosociologie Á Typhaceae Á Espèce menace Á É cologie alluviale Á Conservation Characteristic species and syntaxonomic position of plant communities with Typha minima in the Alps: a contribution to the choice of restoration sites for a threatened species Abstract Dwarf bulrush (Typha minima Hoppe) is declining throughout Europe. A precise knowledge of its ecological niche is required for successful conservation measures, such as the re-introduction or enhancement of populations and river restoration projects. The aim of this study was to identify ecological conditions (soil types, hydrology, vegetation composition) favourable to the establishment of this species through the analysis of ten natural sites along three rivers in the north-western Alps. Dwarf Bulrush was present in two different plant community types, which both included a mixture of ruderal, alluvial and meadow species. Successional pathways were found to differ between montane and lowland sites. Soils were moist, carbonate-rich and sandy to loamy. Results suggest reconsidering the syntaxonomic position of the association Equiseto-Typhetum minimae and placing it within the morainic and alluvial alliance Epilobion fleischeri. Furthermore, frequent companion species, such as Responsible editor: Sabine Güsewell.Matériel électronique supplémentaire La version en ligne de cet article (doi:10.1007/s00035-010-0078-9) contient du matériel supplémentaire qui est accessible aux utilisateurs autorisés.
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