Nutrient availability and plant gender influences on the short-term compensatory response of Salix planifolia ssp. planifolia to simulated leaf herbivory

Males and females of dioecious plants often differ in their biochemistry, physiology, morphology, and (or) ecology. For example, growth rates often are higher for males than for females. Because the ability of plants to compensate for herbivory frequently varies with growth rate, we may expect males and females of dioecious plants to differ in their compensatory ability (hypothesis 1). However, environmental factors such as nutrient availability may influence the expression of such a response (hypothesis 2). For example, low nutrient availability may reduce growth rate and thus restrict compensation. To test these hypotheses, I cloned male and female genets of Salix planifolia Pursh ssp. planifolia from a natural population in northeastern Canada. I then submitted the plants of each sex to two levels of simulated leaf herbivory in combination with two levels of nutrient availability. Contrary to the first hypothesis, plant gender had no significant effect on the compensatory response to simulated leaf herbivory. However, nutrient availability modulated the compensatory ability of plants of both sexes, therefore supporting hypothesis 2. Herbivory may thus be more detrimental to the performance of S. planifolia individuals in low-nutrient environments, such as on dunes or rock outcrops.