Reintroduction of a rare arable weed: Competition effects on weed fitness and crop yield

Arable weeds have severely declined due to intensification of farming during the past decades, and some of them are close to extinction in large parts of western and central Europe. Recent conservation strategies suggest reintroduction of rare arable weeds to suitable types of land use, for example organic fields. To test the feasibility of this conservation option we investigated the effects of spring wheat and a common weed (Stellaria media) on growth and reproduction of a rare weed (Legousia speculum-veneris) in a semi-open glasshouse experiment. Additionally, the impact of the weeds on crop yield was assessed. Aboveground biomass and seed production of L. speculum-veneris were significantly reduced under competition with the crop and the common arable weed. With increasing competition L. speculum-veneris allocated disproportionally more resources to seeds. Wheat yield was not affected by the arable weeds. We conclude that L. speculum-veneris is a subordinate species that is negatively affected by more competitive plants. In the presence of wheat the addition of other weeds does not further harm the species. Enhanced allocation to reproduction might be a specific strategy of the species to maintain populations under competition. Reduced crop densities would help reintroducing the species, while yield losses due to reintroduction of that rare arable weed are unlikely.