Sex- and habitat-specific responses of a high arctic willow, Salix arctica, to experimental climate change

Dioecious plant species and those occupying diverse habitats may present sp ecial analytical problems to researchers examining effects of climate chang e. Here we report the results from two complementary studies designed to de termine the importance of sex and habitat on gas exchange and growth of mal e and female individuals of a dioecious, circumpolar willow, Salix arctica, in the Canadian High Arctic. In field studies, male and female willows fro m dry and wet habitats were subjected to passively enhanced summer temperat ure (similar to 1.3 degrees C) using small open-top chambers over three yea rs. Peak season gas exchange varied significantly by willow sex and habitat . Overall net assimilation was higher in the dry habitat than in the wet, a nd higher in females than in males. In the dry habitat, net assimilation of females was enhanced by experimental warming, but decreased in males. In t he wet habitat, net assimilation of females was substantially depressed by experimental warming, while males showed an inconsistent response. Developm ent and growth of male and female catkins were enhanced by elevated tempera ture more than leaf fascicles, but leaf fascicle development and growth var ied more between the two habitats, particularly in males. In a controlled e nvironment study, male and female willows from these same wet and dry habit ats were grown in a 2x2 factorial experiment including 1 x or 2 x ambient [ CO2] and 5 or 12 degrees C. The sexes responded very differently to the exp erimental treatments, but we found no effect of original habitat. Net assim ilation in males was affected by the interaction of temperature and CO2, bu t in females by CO2 only. Our results demonstrate (a) significant intraspec ific and intersexual differences in arctic willow physiology and growth, (b ) that these differences are affected by environmental conditions expected to accompany global climate change, and (c) that sex- and habitat-specific responses should be explicitly accounted for in studies of dioecious specie s.