Despite the importance of flowers for plant fitness, very little is known about the microbial communities of flowers, the factors affecting the assembly of such communities and their impacts on the plant fitness. We have some evidence that neutral processes and priority effects are important drivers of nectar-associated microbial communities. However, pollinators do not interact in the same way with every part of a flower and—from the perspective of microbes—flowers are highly heterogeneous environments. The relative importance of different dispersal mechanisms and selection due to heterogeneity in floral organs remains unknown. In this work, we characterize some of the spatial determinants of community assembly in the yellow monkeyflower (Erythranthe guttata) through sampling of microbial communities at different spatial scales (from parts of the flower to flowers kilometers apart) at the McLaughlin Nature Reserve in Northern California. We sampled petals, anthers, and styles from flowers from different locations along five different serpentine seeps and obtained 16s amplicon data from each of these organs. At each of this locations, we excluded pollinators from half of our flowers. In addition, we recorded visitation and flower abundances at each location.
Results/Conclusions
Consistent with strong micro-environment selection at the organ level we observed significant differences in community composition across flower organs and only a small effect of seep. In contrast, pollinator treatment was not significant and we did not observe a relationship between microbial diversity and pollinator visitation. Similarly, we observed a relationship between distance and beta-diversity but there was no effect of pollination treatment in this relationship. This study provides evidence of the importance of floral microenvironment in shaping microbial composition and might have important consequences for the ways in which flowers and microbes interact.