title: Invasive insect effects on nitrogen cycling and host physiology are not tightly linked.
abstract: Invasive insects may dramatically alter resource cycling and productivity in forest ecosystems. Yet, although responses of individual trees should both reflect and affect ecosystem-scale responses, relationships between physiological- and ecosystem-scale responses to invasive insects have not been extensively studied. To address this issue, we examined changes in soil nitrogen (N) cycling, N uptake and allocation, and needle biochemistry and physiology in eastern hemlock (Tsuga canadensis (L) Carr) saplings, associated with infestation by the hemlock woolly adelgid (HWA) (Adelges tsugae Annand), an invasive insect causing widespread decline of eastern hemlock in the eastern USA. Compared with uninfested saplings, infested saplings had soils that exhibited faster nitrification rates, and more needle (15)N uptake, N and total protein concentrations. However, these variables did not clearly covary. Further, within infested saplings, needle N concentration did not vary with HWA density. Light-saturated net photosynthetic rates (Asat) declined by 42% as HWA density increased from 0 to 3 adelgids per needle, but did not vary with needle N concentration. Rather, Asat varied with stomatal conductance, which was highest at the lowest HWA density and accounted for 79% of the variation in Asat. Photosynthetic light response did not differ among HWA densities. Our results suggest that the effects of HWA infestation on soil N pools and fluxes, (15)N uptake, needle N and protein concentrations, and needle physiology may not be tightly coupled under at least some conditions. This pattern may reflect direct effects of the HWA on N uptake by host trees, as well as effects of other scale-dependent factors, such as tree hydrology, affected by HWA activity.
authors.affiliation: Louis Calder Center, Department of Biological Sciences, Center for Urban Ecology, Fordham University, Armonk, NY 10504, USA.
authors.forename: Lucy
authors.initials: L
authors.lastname: Rubino
authors.affiliation: Department of Biology, St Francis College, Brooklyn, NY 11201, USA.
authors.forename: Sherley
authors.initials: S
authors.lastname: Charles
authors.affiliation: Louis Calder Center, Department of Biological Sciences, Center for Urban Ecology, Fordham University, Armonk, NY 10504, USA.
authors.forename: Abby G
authors.initials: AG
authors.lastname: Sirulnik
authors.affiliation: Louis Calder Center, Department of Biological Sciences, Center for Urban Ecology, Fordham University, Armonk, NY 10504, USA.
authors.forename: Amy R
authors.initials: AR
authors.lastname: Tuininga
authors.affiliation: Louis Calder Center, Department of Biological Sciences, Center for Urban Ecology, Fordham University, Armonk, NY 10504, USA University of Western Sydney, Hawkesbury Institute for the Environment, Richmond, NSW 2753, Australia jdlewis@fordham.edu.
authors.forename: James D
authors.initials: JD
authors.lastname: Lewis
mesh_terms: D000818:Animals; D017753:Ecosystem; D060434:Herbivory; D007313:Insecta; D009584:Nitrogen / Q000378:metabolism*; D058458:Nitrogen Cycle; D009587:Nitrogen Isotopes / Q000378:metabolism; D010788:Photosynthesis; D010935:Plant Diseases; D018515:Plant Leaves / Q000378:metabolism* / Q000502:physiology; D010940:Plant Proteins / Q000378:metabolism; D012987:Soil / Q000737:chemistry; D013312:Stress, Physiological; D028225:Tsuga / Q000378:metabolism* / Q000502:physiology
chemical_list: D009587:Nitrogen Isotopes; D010940:Plant Proteins; D012987:Soil; D009584:Nitrogen
keywords: Adelges tsugae; N allocation; N cycling; Tsuga canadensis; eastern hemlock; hemlock woolly adelgid; invasive species; photosynthesis