Pollinators mediate floral microbial diversity and network under agrochemical disturbance

How pollinators mediate microbiome assembly in the anthosphere is a major
unresolved question of theoretical and applied importance in the face of
anthropogenic disturbance. We addressed this question by linking
visitation of diverse pollinator functional groups (bees, wasps, flies,
butterflies, beetles, true bugs and other taxa) to the key properties of
floral microbiome (microbial α- and β-diversity and microbial network)
under agrochemical disturbance, using a field experiment of bactericide
and fungicide treatments on cultivated strawberries that differ in flower
abundance. Structural equation modeling was used to link agrochemical
disturbance and flower abundance to pollinator visitation to floral
microbiome properties. Our results revealed that (1) pollinator visitation
influenced the α- and β-diversity and network centrality of floral
microbiome, with different pollinator functional groups affecting
different microbiome properties; (2) flower abundance influenced floral
microbiome both directly by governing the source pool of microbes and
indirectly by enhancing pollinator visitation; and (3) agrochemical
disturbance affected floral microbiome primarily directly by fungicide,
and less so indirectly via pollinator visitation. These findings improve
the mechanistic understanding of floral microbiome assembly, and may be
generalizable to many other plants that are visited by diverse insect
pollinators in natural and managed ecosystems.