Induction and persistence of allelochemicals in the foliage of balsam fir seedlings following simulated browsing
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The intensity, pattern, and timing of browsing disturbances influence the mobilization of chemical defenses (allelochemicals) and subsequent growth of conifers such as balsam fir, an important food source for various insect and mammalian herbivores. The objective of this study was to examine the induction and persistence of allelochemicals in foliage of balsam fir seedlings as affected by the pattern and timing of browsing disturbance. We conducted a simulated browsing study in a greenhouse environment using four browsing patterns and three persistence times. Total phenols were induced shortly after simulated browsing and persisted for at least 1 month, whereas condensed tannins exhibited a delayed induction but were more persistent, remaining above background levels 2 months after simulated browsing. The chemistry of non-browsed seedlings revealed that a seasonal pattern was evident for both total phenols and condensed tannins. As the experiment progressed through the growing season, background levels of total phenols decreased while those of condensed tannins increased with the two allelochemicals groups appearing to show a negative relationship. These trends suggest that total phenols, which are assumed to have a lower biosynthetic cost and are more quickly mobilized than condensed tannins, are a first line of herbivory defense followed by condensed tannins which take longer to mobilize but have a longer persistence time or that total phenols act as a primary defense against insect herbivores which disturb plants in the early growing season while condensed tannins are mobilized in the late season to defend against mammalian browsers of balsam fir in winter.
KeywordsAlces alces Abies balsamea Chemical defense Condensed tannins Phenols Simulated browsing
We are grateful to Barry Linehan and the staff of the Wooddale Provincial Tree Nursery, Newfoundland, for providing the balsam fir seedlings used in this study; Corina Irwin, Laura Rossi, Adrian Faure, Robin Schrader, and Gina Malcolm for help with planting and measuring seedlings; Ashley Ryan for training and assistance with chemical analyses; and Cory Barker and Sharon Sergerie-Groulx for help with grinding foliage samples. For their insightful suggestions which significantly improved the manuscript, we are indebted to Marco Festa-Bianchet and two anonymous reviewers. We especially thank Tom Knight, Parks Canada, Rocky Harbour, NL, for his continued support and encouragement.
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