Adjacent flower strips provide no additional reproductive benefit over permanent grassy field margins for arable weeds

Arable weeds have declined drastically with agricultural intensification, and their loss is linked with the decline of pollinators. While agri-environment measures like flower strips have shown potential in boosting seed-set in adjacent insect-dependent crops, their effect on the reproductive success of arable weeds is less well understood. We conducted a phytometer experiment in conventionally, intensively managed winter cereal fields in Germany, exposing phytometers of three insect pollinated arable plant species ( Sinapis arvensis L. , Centaurea cyanus L. , Consolida regalis Gray) to the available pollinator communities at increasing distances to flower strips and to permanent grassy field margins as a control. Additionally, we compared field pollination to different types of high pollination conditions as well as pollinator exclusion. We measured phytometer reproductive success (seed number, weight, germination rate) and pollinator visitation rate. Seed production in the field trial was reduced compared to our high-pollination trial, suggesting pollination limitation in arable fields. Sinapis arvensis phytometers showed a distance effect, with reduced seed set further away from the margin habitat. Flower strips, as a pollinator-friendly biodiversity measure, did not increase the seed production of the arable plant species compared to permanent grassy field margins. This may be because a high flower density decreases the relative attractiveness of an individual plant, reducing reproductive success. Our results thus suggest that a network of moderately flowering margin vegetation would promote the reproduction of arable plants in crop fields. Both flower strips and grassy strips can contribute to this network, but whilst flower strips are already supported through current agri-environment schemes, introducing financial incentives to create new, or better manage existing, grassy field margins could be an effective way to provide biodiversity benefits.