Variation in leaf lifespan, relative growth rate, and underlying structural leaf traits in wetland plants originating along a latitudinal gradient of growing season length in Ontario

We investigated the growth strategies of 12 graminoid plant species by assessing intraspecific variation in both leaf lifespans and 3 structural leaf traits (specific leaf area, leaf dry matter content, and leaf lamina thickness) in response to a latitudinal gradient of growing season length. Variation in the relative growth rate of above-ground biomass production was also examined far 3 of the species. Plants were collected during the summer of 2002 from 5 regions along a study gradient (range in growing season length = 190 to 154 days) and transplanted into individual pots within a common garden in Sudbury, ON. Intraspecific trends indicated both the establishment of ecotypes along the gradient and the selection of leaf characteristics associated with a rapid growth strategy. Lifespans of leaves emerging late in the season (August) were found to be significantly shorter in plants originating from more northern regions. Leaf dry matter content was found to relate positively and lamina thickness negatively with the gradient of growing season length. Significant intraspecific differences showed plants from more northern regions to possess higher rates of relative growth compared with their southern counterparts. Ecotypic trends may indicate that the shortness of the growing season (disturbance) is a more important selective agent than the harshness of the environment (stress) when shaping competitive, resource-acquiring growth strategies in herbaceous plant life forms.