Drivers of cultivated and wild plant pollination in urban agroecosystems

Pollination is a vital ecosystem service in urban agriculture. Yet the environmental drivers of both crop and wild plant pollination in urban agroecosystems are still not well understood. Pollination experiments involve the manipulation of pollen transfer between plants, for instance, to study the effects of pollinators on fruit and seed production (pollination service). In this study, we conducted a pollination exclusion experiment using four experimental plants: two cultivated plant species, strawberry (Fragaria x ananassa) and chili pepper (Capsicum frutescens), and two wild plant species, buttercup (Ranunculus acris) and clover (Trifolium pratense). We placed experimental plants for over 20 days in 13 urban community gardens in Munich, Germany. We compared fruit and seed mass between “open” and “bagged” flowers and tested the effect of biotic factors (floral resources and pollinator diversity) and abiotic factors (urbanization, microclimate) on pollination service (fruit and seed mass) on the experimental plant species. For the two cultivated plants (F. ananassa and C. frutescens), we found that fruit and seed mass were both positively correlated with temperature and pollinator diversity. For the two wild plants (R. acris and T. pretense), we found that floral abundance was negatively related to R. acris seed mass but was positively related to T. pratense seed mass. In summary, we found that biotic and abiotic parameters affected the plant species studied here in different ways, suggesting that there may be synergies and trade-offs in what factors promote the overall pollination of urban plant communities. Our results suggest that gardeners can potentially increase the pollination services on certain garden plants by providing floral resources for pollinating insects.