Monica Tynan

Project Title: Getting to the root of the problem: The effects of invasive insects on eastern hemlock root structure

Mentor: Evan Preisser

Abstract: The hemlock wooly adelgid (Adelges tsugae; HWA) and the elongate hemlock scale (Fiorinia externa; EHS) are invasive insects from Japan that attack and damage eastern hemlocks (Tsuga canadensis) in the eastern United States. Few studies address the impact of sap-sucking herbivores on belowground processes, yet belowground processes are essential in water and nutrient acquisition in nearly all plants. The effects of these two insects on hemlock belowground biomass, root nitrogen concentrations, specific root length (SRL), and ectomycorrhizal fungi colonization of root tips were analyzed in order to determine correlation between insect infestation and root structure. In May 2015, 88 six-year old hemlock saplings were harvested from the field site at URI East Farm. There were uninfested control (C) trees; trees infested with HWA for either two or four years (HWA2, HWA4); and trees infested with EHS for either two or four years (EHS2, EHS4). Priority and combination treatments were also studied, but this analysis focuses on single-insect trees (N=54). ANOVAs did not reveal a significant difference in the mean percent belowground biomass, the mean percentage of nitrogen found in the roots, or the first and second order SRLs across treatments (all P > 0.05). However, there was a significant difference in the mean proportion of root tips colonized by ectomycorrhizae across treatments (P < 0.001). HWA-infested hemlocks had less roots tips colonized by ectomycorrhizae. This supports evidence that maintaining a resource costly relationship while under attack by insects is taxing on a plant. These results indicate the importance of considering multidimensional interactions within community dynamics. An organism is almost always affected by more than one factor at any given time, and it is crucial to consider these implications within ecosystems.