Green roofs can support pollinator communities in cities. However, little is known about the influence of green roof characteristics such as substrate and vegetation type on the abundance and diversity of attracted pollinators. Here we aimed to assess how green roof design impacts their attractiveness to pollinators. Using mesocosms on a rooftop in Paris (France), we studied the impact of two substrate types, two substrate depths (10 and 30 cm) and either monocultures or mixtures of 5 plant species on plant pollinator interactions. In the case of mixtures, we also tested the effect of substrate type (natural soil vs. artificial substrate). We counted the number of floral units and recorded the visits by pollinators once a week from mid-June to mid-August. The pollinator assemblage visiting plant communities included 4 functional groups of pollinators: domesticated honey bees, bumble bees, solitary bees and syrphid flies. Effects of treatments on pollinator community composition were variable and plant species dependent. Deep monoculture treatments resulted in the highest number of floral units and visits. Although plants grown on natural soil had less floral units than on artificial substrate, both treatments resulted in a similar number of visits. This paper provides evidence that plant-pollinator interactions on green roofs are modulated by substrate type, substrate depth and plant community. We suggest that combining plant species with diverse flowering morphologies and phenologies can enhance pollinator diversity. When possible, increasing substrate depth can result in higher levels of attractiveness.

绿化屋顶可以支撑城市中的传粉媒介社区。但是，关于屋顶绿化特征（如基质和植被类型）对吸引的传粉媒介的丰度和多样性的影响知之甚少。在这里，我们旨在评估绿色屋顶设计如何影响其对传粉媒介的吸引力。我们在法国巴黎的屋顶上使用中观空间，研究了两种基质类型，两种基质深度（10和30 cm）以及单一栽培或5种植物混合物对传粉媒介相互作用的影响。对于混合物，我们还测试了底物类型的影响（天然土壤与人工基材）。我们计算了花卉单位的数量，并记录了授粉媒介从6月中旬到8月中旬每周进行的造访。授粉媒介组合到访植物群落包括四个功能性的授粉媒介群：驯养的蜜蜂，大黄蜂，孤蜂和蓝蝇。处理对传粉媒介群落组成的影响是可变的，并且取决于植物种类。深层单培养处理导致最多的花卉单位和造访次数。尽管在天然土壤上生长的植物比在人工基质上生长的植物具有更少的花单位，但两种处理均导致相似的造访次数。本文提供的证据表明，绿色屋顶上的植物-授粉媒介相互作用受基质类型，基质深度和植物群落的调节。我们建议将具有不同开花形态和物候特征的植物物种结合起来可以增强授粉媒介的多样性。可能的话，增加基材深度可导致更高水平的吸引力。