Age-related shifts in leaf chemistry of clonal aspen (Populus tremuloides).

Developmental changes in plant structure and function can influence both mammalian and arthropod feeding preferences for many woody plant species. This study documents age-related changes that occur in the leaf chemistry of trembling aspen (Populus tremuloides Michx., Salicaceae) and discusses implications for the herbivore community and ecosystem processes. We collected leaves from replicate ramets from six age classes (1-25+ yr) in each of seven aspen clones growing in south central Wisconsin, USA. Chemical analyses were conducted to determine concentrations of condensed tannins, phenolic glycosides (salicortin and tremulacin), nitrogen, starch, and soluble sugars. Each variable differed significantly among clones and among age classes. On average, condensed tannin concentrations doubled in the first five years and then remained fairly constant among older age classes. Combined phenolic glycoside (salicortin + tremulacin) concentrations were high in the youngest ramets (ca. 19%) and decreased sharply with age. Developmental changes in tannin, salicortin, and tremulacin concentrations exceeded those of nitrogen and carbohydrates. Developmental shifts of this magnitude, and the age-related tradeoff that occurs between condensed tannins and phenolic glycosides, are likely to have significant influence on the herbivore community of aspen and may influence leaf litter decomposition and nutrient cycling.