RESPONSES OF DRYAS-OCTOPETALA TO ITEX ENVIRONMENTAL MANIPULATIONS - ASYNTHESIS WITH CIRCUMPOLAR COMPARISONS

We have examined organismic responses of Dryas octopetala to simulated changes in the summer climate at four tundra sites as part of the Int ernational Tundra Experiment (ITEX). Our study sites are located in th e High Arctic, on Svalbard, Norway in the Low Arctic at Abisko, Sweden , and at Toolik Lake, Alaska, USA and our temperate alpine site is at Niwot Ridge, Colorado, USA. These sites represent a range of tundra te mperature and precipitation regimes, being generally cold and dry in t he High Arctic and warmer and wetter at Toolik Lake and Niwot Ridge. R esults from our studies indicate organismic attributes such as floweri ng shoot length varies by 30% between low and high arctic populations and that experimental warming results in significant increases in shoo t height at three of four sites. We find that phenological development of Dryas is accelerated under experimentally warmed conditions which corresponds with a lengthening of the growing season in autumn, greate r degrees of seed set and a higher likelihood of colonization of bare ground. We also observe that Dryas dominated ecosystems which are expo sed to experimental manipulations are capable of exhibiting net carbon sequestration in late autumn, and that Dryas photosynthesis and green leaf biomass is significantly greater under warmer as opposed to ambi ent temperature conditions. Dryas leaf nitrogen is also significantly lowered under warmer conditions resulting in senescent leaves having a higher C:N ratio than those under ambient conditions. Together these findings indicate that Dryas phenology and carbon flux may be altered to the greatest degree in spring and again in autumn by higher summer temperatures and that simultaneously both positive and negative feedba ck effects may result from changes in plant and ecosystem performance.