The Water Relations of Carex stans in Wet Sedge-Moss Tundra at a High Arctic Oasis, Devon Island, N.W.T., Canada

Abstract

In the eastern Canadian High Arctic, wet sedge-moss tundras, dominated by Carex stans, are usually associated with oases where ameliorated physical conditions allow relatively high plant production. Although Carex 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 resulted in leaf temperatures up to 10'C higher than that of the air. Trends in transpiration rate closely followed those in solar irradiance, air and leaf temperature and the leaf-to-air vapor pressure difference. Transpiration also exhibited significant positive correlations with soil temperature and wind speed. The maximum stomatal conductance in Carex stans (0.16 mol m-2 S-1) was considerably lower than maxima reported for polar semidesert graminoids; furthermore, the maximum rate in Carex was seldom achieved. Stomatal conductance showed strongest positive correlations with solar irradiance, leaf temperature, and leaf-toair temperature and vapor pressure differences, and showed a strong negative correlation to soil temperature at -10 cm. Carex leaf water potentials ranged from -0.65 to -2.26 MPa, suggesting a water status more characteristic of polar semidesert graminoids than those of wet tundra. Leaf water potential was most highly correlated with air temperature and air vapor pressure deficit. Several anomalous relationships between stomatal conductance and other variables were observed. For example, stomatal conductance did not respond to changes in leaf water potential, was insensitive to changes in air vapor pressure deficit and was positively correlated with the leaf-to-air vapor pressure difference when a negative correlation was expected. Water stress in Carex 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 year despite considerable annual variation in thermal inputs. We propose that in relatively warm summers, high arctic tundras dominated by Carex stans show no increased productivity due to greater instances of water stress and stomatal closure.