Data from: 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 feeding had no observable effects on root functional traits (e.g., specific root length) or on resource allocation to roots. HWA feeding did significantly reduce EMF colonisation of hemlock fine roots, though surprisingly, EMF diversity and that of other fungal associates were unaffected. In contrast to HWA, EHS (alone or in conjunction with HWA) feeding had no observable effect on belowground traits or EMF colonisation alone; however, its presence mediated HWA effects when trees were co-infested. Simultaneous infestation within the same year yielded significant reductions in EMF colonisation, while prior EHS attack weakened HWA effects. Our results collectively suggest that prior EHS attack dampens the impact of HWA on belowground functional traits. This highlights how the timing and sequence of herbivore arrival can alter plant-mediated interactions between herbivores and their effects on above-belowground linkages and associated tree health.

森林害虫通过破坏与养分获取、生长及繁殖相关的功能性状，导致树木死亡。单一或多种地上植食性昆虫的取食对树木健康至关重要的根系功能性状的影响，却鲜有研究关注，这一点在外来植食性昆虫——这类常栖息于受干扰森林中的生物——身上体现得尤为明显。我们挖掘了完整根系，样本来自经人工接种铁杉球蚜（hemlock woolly adelgid, HWA: Adelges tsugae）、长形铁杉介壳虫（elongate hemlock scale, EHS: Fiorina externa）单独或复合侵染的东部铁杉（Tsuga canadensis）植株，接种时长分别为2年和4年。我们测定了地下根系生物量、功能性状与储藏养分，以评估植食作用的影响。同时量化了细根的外生菌根真菌（ectomycorrhizal fungal, EMF）定殖率，并采用非培养法探究EMF的多样性。接种铁杉球蚜的植株根质量分数（根总生物量比）更高，但其取食对根系功能性状（如比根长）或根系的资源分配无显著影响。铁杉球蚜取食虽显著降低了铁杉细根的外生菌根真菌定殖率，但令人意外的是，EMF多样性及其他真菌共生体的多样性并未受到影响。与铁杉球蚜不同，长形铁杉介壳虫（单独或与铁杉球蚜复合侵染）的取食对地下性状或单独的EMF定殖率无明显影响；但当植株被复合侵染时，其存在会调控铁杉球蚜的作用效果。同年份同时侵染会导致EMF定殖率显著降低，而预先受到长形铁杉介壳虫侵染则会削弱铁杉球蚜的影响。我们的研究结果整体表明，预先受到长形铁杉介壳虫侵染会缓解铁杉球蚜对地下功能性状的影响。这凸显了植食性昆虫的到达时间与顺序，如何改变植食性昆虫之间的植物介导互作，及其对地上-地下联系与相关树木健康的影响。