Abstract
In frequently disturbed environments, plant community assembly mainly results from spatial dispersal and temporal dispersal through seed bank. Here, we propose to quantify the relative contributions of temporal and spatial dispersal on weed species assembly in farmlands. Weeds are mostly annual plants that rely exclusively on seeds for perpetuation, the latter presenting various level of longevity and dispersal capacity according to the species. In farmland, arable fields surrounded by landscape with high proportion of grasslands harbor high level of weed diversity revealing important dispersal flux. Similarly, the presence of grasslands in the past history (i.e crop succession) of the field promotes actual weed community diversity thanks to temporal dispersion through the seed bank. Therefore, grasslands favor weed diversity both by being present in the surrounding landscape and in the crop succession. However whether the effect of grasslands is higher in space or time remains unknown mainly because their presence in space and time are generally correlated. We tested the effect of the presence of grasslands (percentage and distance in space vs time) by analyzing weed diversity in winter wheat fields in the LTER ‘Zone Atelier Plaine et Val de Sèvre’ (France; www.za.plainevalsevre.cnrs.fr). We selected fields so that the presence of grasslands were not correlated in space and time. We then calculated weed taxonomic and functional diversity using Hill’s numbers. Selected traits for functional analysis were seed mass, seed form, seed lipid content, plant height and dormancy levels since they are known to be involved in plant spatio-temporal dispersal. Preliminary results suggest a higher impact of grassland in time than in space on weed diversity. Weed seeds traits diversity may give interesting insights about weed species assembly processes.