THE WATER RELATIONS OF CAREX STANS IN WET SEDGE-MOSS TUNDRA AT A HIGHARCTIC OASIS, DEVON ISLAND, NWT, CANADA

In the eastern Canadian High Arctic, wet sedge-moss tundras, dominated by Carer stans, are usually associated with ''oases'' where ameliorat ed physical conditions allow relatively high plant production. Althoug h Carer stans occurs in water-saturated soils, low transpiration rates , stomatal conductances and leaf water potentials indicated that mild water stress was common in this species. Low transpiration rates under conditions of relatively high solar irradiance and air temperature re sulted in leaf temperatures up to 10 degrees C higher than that of the air. Trends in transpiration rate closely followed those in solar irr adiance, air and leaf temperature and the leaf-to-air vapor pressure d ifference. Transpiration also exhibited significant positive correlati ons with soil temperature and wind speed. The maximum stomatal conduct ance in Carex stans (0.16 mol m(-2) s(-1)) was considerably lower than maxima reported for polar semidesert graminoids; furthermore, the max imum rate in Carer was seldom achieved. Stomatal conductance showed st rongest positive correlations with solar irradiance, leaf temperature, and leaf-to-air temperature and vapor pressure differences, and showe d a strong negative correlation to soil temperature at -10 cm. Carex l eaf water potentials ranged from -0.65 to -2.26 MPa, suggesting a wate r status more characteristic of polar semidesert graminoids than those of wet tundra. Leaf water potential was most highly correlated with a ir temperature and air vapor pressure deficit. Several anomalous relat ionships between stomatal conductance and other variables were observe d. For example, stomatal conductance did not respond to changes in lea f water potential, was insensitive to changes in air vapor pressure de ficit and was positively correlated with the leaf-to-air vapor pressur e difference when a negative correlation was expected. Water stress in Carer stans is hypothesized to result from low soil temperatures and poor soil aeration, characteristics of sedge-moss meadows which result from their waterlogged condition. Several studies have reported that productivity of wet graminoid tundra remains constant from year to yea r despite considerable annual variation in thermal inputs. We propose that in relatively warm summers, high arctic tundras dominated by Care r stans show no increased productivity due to greater instances of wat er stress and stomatal closure.