VARIATION IN LEAF DISSECTION AND LEAF ENERGY BUDGETS AMONG POPULATIONS OF ACHILLEA FROM AN ALTITUDINAL GRADIENT

The degree of leaf dissection differs dramatically among populations of the Achillea millefolium complex along an altitudinal gradient in the Sierra Nevada. The purpose of this study was to determine whether there was a genetic basis to differences in leaf shape among populations, and also to determine the importance of genetic variability within populations, plastic responses of leaf shape to the growth environment, and genetic differences among populations in plastic response to the environment. A second major goal of the research was to investigate the effects of differences in leaf dissection on the capacity for leaf temperatures to become uncoupled from air temperatures. Greenhouse experiments using clonal replicates of plants collected at different altitudes revealed that there were genetic differences among populations in the degree of dissection, and that other sources of phenotypic variation, such as plasticity, were also significant. Leaves from the highest altitude population had the most compact shape under all conditions, while those from lower altitude populations were always more open and highly dissected. In both simulations and actual measurements the dissected leaves of low altitude plants remained close to air temperatures, while the compact leaves of high altitude plants had the capacity to warm up substantially above air temperatures.