Seasonal changes in eastern hemlock (Tsuga canadensis) foliar chemistry

Ian G Kinahan,Brenton L Deboef,Chad M Rigsby,Anita Oppong-Quaicoe,Evan L Preisser,Colin M Orians,Andrew S Marsella,Suzanne K Savage,Nick L Houseman

doi:10.1139/cjfr-2019-0408

Abstract

Eastern hemlock (Tsuga canadensis (L.) Carrière) is an eastern North American conifer threatened by the invasive hemlock woolly adelgid (Adelges tsugae Annand). Changes in foliar terpenes and phenolics were evaluated in new (current-year growth) and mature (1-year-old growth) hemlock needles during the growing season and into plant dormancy. From April through September, foliar concentrations of nonvolatile soluble phenolics, condensed tannins, lignin, mono- and sesquiterpenes, α-pinene, camphene, isobornyl acetate, and diterpene resin were quantified. After September, additional analyses of metabolites that continued to differ significantly between new and mature foliage were carried out. Total soluble phenolic and condensed tannin concentrations in new foliage remained low relative to those of mature foliage throughout the growing season and converged in December. Lignin concentration in new foliage converged with that of mature foliage by July. Concentrations of α-pinene, camphene, isobornyl acetate, and diterpene resin in new foliage converged with those of mature foliage within 1 month of budbreak. The convergence of terpene concentrations in new and mature foliage suggests that these metabolites may play a role in herbivore defense during the peak growing season. Conversely, soluble phenolics, including condensed tannins, may defend foliage from herbivory outside of the spring growth period.

Highlights

Phenology is the study of seasonally varying developmental events driven by environmental cues
Total soluble phenolic and condensed tannin concentration was lower in new relative to mature foliage throughout the growing season (May through September)
It took until December for concentrations of total soluble phenolics and condensed tannins in new and mature foliage to converge

Summary

Introduction

Phenology is the study of seasonally varying developmental events driven by environmental cues. Plant phenology is characterized by temporal patterns of growth associated with abiotic factors such as degree day, amount of transmitted light, and precipitation Leaf growth and development occur largely during a specific time of year (Fenner 1998). In temperate forests of the northern hemisphere, for example, plants leaf out rapidly in the spring to take full advantage of the growing season. Rapid leaf expansion/development is associated with substantial physiological changes during tissue maturation (Koricheva and Barton 2012; Wiggins et al 2016). Czerepanovii Ehrhart), for example, leaf toughness increases, amino acid levels decrease, and different phenolic compounds (e.g., proanthocyanidins, gallotannins, flavonoids) show discrete accumulation patterns throughout the growing season (Riipi et al 2002) In mountain birch (Betula pubescens subsp. czerepanovii Ehrhart), for example, leaf toughness increases, amino acid levels decrease, and different phenolic compounds (e.g., proanthocyanidins, gallotannins, flavonoids) show discrete accumulation patterns throughout the growing season (Riipi et al 2002)

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Conclusion