| The purpose of this research was to describe the initial, short-term responses of high arctic plant species to experimental conditions simulating predicted climate changes. This work was conducted at Alexandra Fiord on Ellesmere Island, Canada, as part of the International Tundra Experiment (ITEX).; Beginning in 1992, tundra soil was warmed up to 6{dollar}spcirc{dollar}C above control plots using small, open-top greenhouses. For the arctic willow, Salix arctica, catkin and leaf fascicle lengths, stem increments, and specific leaf areas were greater for experimentally warmed plants, and the effect was substantially more pronounced for willows in a dry (vs. wet) community over three seasons. Reproduction and phenology were only slightly affected by warming. There was evidence of a cumulative effect of warming over time on most of the variables examined. Diurnal gas exchange, examined in 1992 and 1993, was highly dependent upon the sex of the plant and the habitat in which it grew. In the dry habitat, warming enhanced net assimilation (NA) in females but depressed it in males; stomatal conductance (g{dollar}sb{lcub}rm s{rcub}){dollar} was unaffected by warming. In the wet habitat, NA in female willows was depressed by warming but enhanced in males; g{dollar}sb{lcub}rm s{rcub}{dollar} was depressed in both sexes. In controlled environments, elevated atmospheric CO{dollar}sb2{dollar} and temperature had a significant, positive effect on NA, g{dollar}sb{lcub}rm s{rcub},{dollar} dark respiration, and water use efficiency in S. arctica grown under well-watered conditions. No downward regulation of NA was observed over time, and leaf age had little effect on photosynthesis. With soil drying, NA increased at high CO{dollar}sb2{dollar} concentrations, but remained unchanged at ambient concentrations. Constant {dollar}rm Csb{lcub}i{rcub}/Csb{lcub}a{rcub}{dollar} ratios indicated stomatal sensitivity to increased carbon demand.; Diurnal gas exchange was examined in three sedge species on hummocks and in hollows in the wet community during 1992 and 1993. Experimental warming significantly depressed NA in the sedge Eriophorum angustifolium triste, but differences between hummock and hollow microsites were minimal. In contrast, experimental warming had little effect on Carex aquatilis stans, but plants growing on hummocks had significantly higher NA than plants in the hollows. |
