Individual and non-additive effects of exotic sap-feeders on root functional and mycorrhizal traits of a shared conifer host

Forest pests drive tree mortality through disruption of functional traits linked to nutrient acquisition, growth, and reproduction. The impacts of attack by individual or multiple aboveground herbivores on root functional traits critical to tree health have received little attention. This is especially true for exotic herbivores, organisms often found in disturbed forests.
We excavated whole-root systems from eastern hemlock (Tsuga canadensis) individuals experimentally infested with hemlock woolly adelgid (HWA: Adelges tsugae) and elongate hemlock scale (EHS: Fiorina externa) individually, or in combination, for periods of two and four years. Belowground root biomass, functional traits, and storage nutrients were measured to assess impacts of herbivory. We also quantified ectomycorrhizal fungal (EMF) colonisation of fine roots and used culture-independent methods to examine EMF diversity.
Trees infested with HWA had a greater root mass fraction (root to total biomass ratio), although...