Mesocosm evaluation of the competittive ability of common and segetal weed species against barley

International audienceIn conventional cropping systems, arable weed species have always been considered undesirable because their presence can significantly reduce the yield and quality of the crop. Among the weed community, segetal weeds particularly inhabit winter cereal fields and are generally described as rare species (Jauzein, 1997). Following the observed decline in biodiversity in the field, there is a renewed interest in conserving segetal weeds as they represent an invaluable plant heritage as wild relatives of cultivated plants (Fried, 2020). The origin of the regression of these particular annual species is strongly linked to intensive agricultural practices (herbicides, fertilization) but also probably to a poorer competitive ability with recent selected cereal crops unlike common species (Denelle et al., 2020). To study in detail the competitive ability of these two categories of weeds, a wide range of species (7 segetal and 16 common species) was studied in the presence of a spring barley crop (Hordeum vulgare L.). For that purpose, experiments were carried out using mesocosms (rectangular plastic pot) as experimental units. Each mesocosm was divided into three studied zones: one quarter was dedicated to the growth of barley alone (Zone1), another quarter was dedicated to a weed alone (Zone4) and the remaining half was a mixture of barley and weeds (Zone2&3). For each mesocosm, only one weed species was considered. In total, on the 23 mesocosms, different competitiveness traits were measured during the plant development cycle between March and June 2021: plant height, above-ground biomass and total plant biomass. The calculation of the Relative Competitive Performance index (RCP) with height as a competitive trait revealed different competitive effects caused by weeds and a ranking of the weeds according to their competitive power is proposed and compared to the literature. Under the conditions of our experiment, it does not seem that segetal species showed a lower ability to compete than common specie