Seasonal variation in effects of herbivory on foliar nitrogen of a threatened conifer. Issue 2 (28th February 2017)

• Record Type: Journal Article
• Authors: Schaeffer, Robert N.; Soltis, Nicole E.; Martin, Jennifer L.; Brown, Aden L.; Gómez, Sara; Preisser, Evan L.; Orians, Colin M.
• Is Part Of: AoB plants. Volume 9:Issue 2(2017)
• Publication Date: 2017-02-28
• Subjects: Adelges tsugae -- nitrogen remobilization -- nitrogen storage -- protein -- Tsuga canadensis; Plants -- Periodicals; Botany -- Periodicals; 580.5
• DOI: 10.1093/aobpla/plx007
• Languages: English
• ISSNs: 2041-2851

Abstract

Abstract : Invasive herbivores can dramatically impact the nitrogen (N) economy of native hosts. In eastern forests of the United States, the foundational conifer eastern hemlock (Tsuga canadensis) is under threat of extirpation by the invasive hemlock woolly adelgid (HWA: Adelges tsugae). Our study suggests that HWA-induced mobilization of N to local feeding sites and its rapid depletion may be a significant contributor to eastern hemlock mortality in U.S. forests. Abstract: Invasive herbivores can dramatically impact the nitrogen (N) economy of native hosts. In deciduous species, most N is stored in stem tissues, while in evergreen conifer species N is stored in needles, making them potentially more vulnerable to herbivory. In eastern forests of the USA, the long-lived, foundational conifer eastern hemlock ( Tsuga canadensis ) is under the threat of extirpation by the invasive hemlock woolly adelgid (HWA: Adelges tsugae ). We assessed the impact of HWA infestation on the patterns of seasonal foliar N availability in hemlock planted in a deciduous forest understory. Over the course of a year, we sampled needles and twigs and measured N, carbon (C), C:N ratio, and total protein concentrations. Tissue sampling events were timed to coincide with key life-history transitions for HWA to determine the association between HWA development and feeding with these foliar nutrients. In uninfested trees, needle and twig N concentrations fluctuated across seasons, indicating the potential importance of N storage and remobilization for the N economy of eastern hemlock. Although N levels in HWA-infested trees also cycled annually, the degree to which N concentrations fluctuated seasonally in tissues was significantly affected by HWA feeding. These fluctuations exceeded N levels observed in control trees and coincided with HWA feeding. HWA feeding generally increased N concentrations but did not affect protein levels, suggesting that changes in N do not occur via adelgid-induced protein breakdown. Herbivore-induced mobilization of N to feeding sites and its rapid depletion may be a significant contributor to eastern hemlock mortality in US forests.