Microbial Communities in Tree Exudates and Their Role in Saproxylic Hoverfly Conservation

A total of 105 sap-run samples were collected from 35 sites and analyzed through 16S rDNA metabarcoding using Oxford Nanopore sequencing. Samples were processed using standardized DNA extraction, amplification and sequencing protocols for microbiome analysis. Alpha diversity indices (Observed, Shannon, Simpson) revealed significant differences among host tree species, with Populus sp. and Ulmus sp. showing higher richness and evenness compared to Acer negundo and Quercus rubra, suggesting that sap physicochemical properties influence microbial diversity. Beta diversity analyses showed significant differences in community composition across all tested factors. Tree species shaped microbial assemblages, while hoverfly colonization and environmental context were associated with partial but significant compositional shifts. Key taxa driving these patterns included fermentative and polysaccharide-degrading bacteria such as Cereibacter azotoformans and Dysgonomonas alginatilytica, as well as insect-associated taxa like Collinsella intestinalis and Erysipelothrix larvae. These findings indicate that sap-run microbial communities are structured by multiple interacting factors, where plant traits primarily influence diversity, while insects and environmental conditions drive compositional turnover. Overall, sap-runs emerge as dynamic microhabitats shaped by multitrophic interactions, with implications for the ecology and conservation of saproxylic hoverflies.