Interactions of farming and plant biodiversity in weed control related ecosystem service provision and weed conservation

There is evidence that diverse plant communities in terrestrial ecosystems are either more stable or more productive in terms of food web support and ecosystem service provision. In agro-ecosystems, characterized by high disturbance and external inputs, plant diversity and their services can only be provided by weeds. \nIn the first study, vegetation recordings and farmer surveys were conducted in on-farm experiments in two regions of Southwestern Germany. The aim was to examine the effects of agricultural management on weed community composition, weed biodiversity and occurrence of rare arable weed species in cereal fields. Weed biodiversity was influenced mainly by crop species, herbicide use and farming system as well as nitrogen and light availability. Weed communities were quite similar in both study regions and dominated by Alopecurus myosuroides, Galium aparine, Viola arvensis, Polygonum convolvulus and Veronica persica. A redundancy analysis revealed that the weed community was mainly shaped by crop species, tillage, location in the field and timing of herbicide application. The results highlight the erosion of weed communities due to intensive agricultural practices and emphasize the conservation of weed biodiversity per se and rare arable weed species in particular.\nThe next aim was to examine if this biodiversity is able to support weed control related ecosystem services, like the predation of weed seeds. The objectives of this study were to investigate the connection between weed biodiversity, Carabid beetle diversity and weed seed predation as well to evaluate the role of farming intensity in this sequence. For this purpose, on-farm experiments were performed on the Eastern Swabian Alb. A positive correlation between weed biodiversity and Carabid beetle diversity was identified as well as a pattern of medium Carabid beetle diversity providing the highest weed seed predation. There was no consistent influence of farming intensity on weed seed predation. The revealed connection between weed diversity, Carabid beetle diversity and weed seed predation highlights the role of plants in food web support and subsequent ecosystem service provision. The utilization of these services depends on the promotion of biodiversity by designing appropriate management strategies.\nIn the next step, the general principles underlying ecosystem service provision by biodiversity, were conveyed to a cover cropping system. The aim was to test single sown cover crops and species mixtures in terms of weed suppression efficacy and reliability. For this purpose, cover crop species were sown singly and as mixtures in a field experiment. Lower weed dry matter and weed densities were found predominantly in treatments with favorable establishment and above-average biomass production. Mixtures performed much more homogeneous in regard to the measured parameters compared to single sown cover crops. The results suggest that, although particular single sown cover crops are more effective to control weeds than mixtures, mixtures are more reliable under changing conditions. Altering the species composition of cover crop mixtures according to more complementary traits might further improve their weed control efficacy.\nThe results of this dissertation demonstrate the importance of plant biodiversity in the provision and reliability of weed control related ecosystem services, either by weeds themselves or by specifically designed cover crop mixtures. Furthermore, management factors influencing weed biodiversity were determined, which can aid in the creation of more sustainable management strategies for a diverse agroecosystem and the conservation of rare arable weed species.