East Tennessee State University Johnson City, Tennessee, United States
Abstract: Up to 96% of angiosperms are dependent on animal pollinators for successful reproduction thus providing a key ecosystem service. Recent studies however, have indicated that micro-organisms inhabiting floral nectar can influence interactions between plants and their pollinators with consequences for plant fitness. Specifically, floral nectar provides suitable habitat for fungal and bacterial species i.e., the nectar microbiome (NMB), which can alter the amount and quality of nectar, floral volatile composition and impact pollinator preference and plant reproductive success. While the extent and consequences of these interactions are well understood for one or few plant species, community-level studies on the structure, drivers and fitness consequences of interactions between plants and nectar inhabiting microorganism are scarce. Community-level of studies of the drivers and consequences of interactions between plants and nectar microorganisms can help advance our understanding of the mechanisms that mediate the structure of plant-pollinator networks and mediate plant community assembly. In this study, we describe the structure of a plant-nectar microbiome network in a serpentine plant community in Northern California. We further evaluate how the structural properties of such network are mediated by the abundance and diversity of floral visitors and its effects on plant reproductive success. Nectar samples were collected from 15 plant species and cultured on agar plates until isolated. Fungal ITS and bacterial 16s DNA sequences were used for identification by Sanger sequencing. We further explored the effects pollinator visitation on of plant-microbiome network properties and the effects of the latter on pollen deposition and pollen tube production.
Plant-nectar microbiome network was composed of 52 fungal and 27 bacterial morphospecies (79 total cultured CFU). Filamentous fungi (i.e. molds) comprise 80% of all fungal colonies. Network analysis also revealed network connectance and specialization were lower (0.07 and 0.39 respectively) than reported for plant-pollinator networks in the same community. On average, individual plants have 2.32 links with modularity and nestedness values of 0.36 and 0.32, respectively, which are comparable to plant-pollinator network values. An increase in diversity of insect visitors species significantly increased NMB richness. Furthermore, increased NMB species richness seemed to have a marginal positive effect on conspecific pollen deposition but nor on pollen tube production. Our results suggest that community-level patterns of NMB composition can be determined by the diversity and abundance of the pollinator community, with potential consequences for plant reproductive success.
