Characterizing the nectar microbiome of the non-native tropical milkweed, Asclepias curassavica, in an urban environment

In increasingly urban landscapes, the loss of native pollen and nectar floral resources is impacting ecologically important pollinators. Increased urbanization has also brought about the rise of urban gardens which introduce new floral resources that may help replace those the pollinators have lost. Recently, studies have shown that the microbial communities of nectar may play an important role in plant-pollinator interactions, but these microbial communities and the floral visitors in urban environments are poorly studied. In this study we characterized the floral visitors and nectar microbial communities of Ascelpias curassavica, a non-native tropical milkweed commonly, in an urban environment. We found that the majority of the floral visitors to A. curassavica were honey bees followed closely by monarch butterflies. We also found that there were several unique visitors to each site, such as ants, wasps, solitary bees, several species of butterflies and moths, Anna’s hummingbird, and the tarantula hawk wasp. Significant differences in the nectar bacterial alpha and beta diversity were found across the urban sites, although we found no significant differences among the fungal communities. We found that the differences in the bacterial communities were more likely due to the environment and floral visitors rather than physiological differences in the plants growing at the gardens. Greater understanding of the impact of urbanization on the nectar microbiome of urban floral resources and consequently their effect on plant-pollinator relationships will help to predict how these relationships will change with urbanization, and how negative impacts can be mitigated through better management of the floral composition in urban gardens.

在日益城市化的景观中，本土花粉与花蜜类花卉资源的流失正严重威胁具有重要生态价值的传粉昆虫。快速推进的城市化同时催生了城市花园的兴起，其引入的新型花卉资源或可弥补传粉昆虫所丧失的本土食物来源。近期研究表明，花蜜微生物群落可能在植物-传粉者互作中发挥关键作用，但目前针对城市环境中的此类微生物群落与花卉访生者的研究仍较为匮乏。本研究针对城市环境中常见的外来热带马利筋（Ascelpias curassavica）的花卉访生者与花蜜微生物群落展开了表征分析。结果显示，到访该马利筋的花卉访生者以蜜蜂占比最高，其次为帝王蝶。此外各采样点均存在独特的访生类群，包括蚂蚁、胡蜂、独居蜂、多种蝶类与蛾类、安娜蜂鸟以及狼蛛鹰蜂。不同城市采样点的花蜜细菌群落α多样性与β多样性均存在显著差异，但真菌群落并未表现出显著的组间差异。进一步分析发现，细菌群落的组间差异更可能源于采样环境与花卉访生者的差异，而非园内植株的生理性状区别。加深对城市化如何影响城市花卉资源的花蜜微生物组，及其进而对植物-传粉者互作关系产生的效应的认知，将有助于预测此类互作关系随城市化进程的变化趋势，并为通过优化城市花园的花卉组成以缓解负面影响提供理论支撑。