Alaska州Barrowの湛水ツンドラにおける2000年度植物生育期間のCO₂フラックスの季節変化とCO₂収支

抄録

The CO₂ flux of a wet sedge tundra ecosystem in the Arctic, at Barrow, Alaska, was measured applying an eddy correlation method. The seasonal change of CO₂ uptake by the vegetation and the net CO₂ budget through the growing period were examined for the 2000 growing season. Tundra CO₂ budget analysis model(TCBM) was applied to examine the vegetation responses to the environmental variables. Photosynthesis of the vegetation was well parameterized as functions of measured solar radiation, R_sd and air temperature, T_a, and ecosystem respiration was determined as a function of soil temperature at 0.01 m depth, T_s. Estimated CO₂ flux by TCBM with measured R_sd and T_a was verified by comparison with observed CO₂ flux, and then was used for gap-filling of data missing or eliminated data during the quality control. Parameters of TCBM functions were in accordance with previous studies; temperature dependence of the ecosystem respiration Q₁₀ was 2.6, peak levels of photosynthesis-light response curve ranged 0.12-2.43gCO₂m^-2h^-1 with optimum air temperature of 0.5-14.0°C, with high levels in late July, and the initial slope of the curve ranged 0.002-0.067 gCO₂ W^-1h^-1. Daily CO₂ flux was almost 0gCO₂ m^-2d^-1 while the snow covered the ground. Then that changed to a source of up to 1.6gCO₂m^-2d^-1 for about a week after snowmelt. After mid June, CO₂ flux was a sink until mid September; those levels showed clear seasonal trends with a maximum of −17.8gCO₂ m^-2d^-1 occurring on August 2. The Tundra ecosystem at Barrow accumulated −335gCO₂ m^-2 during 122 days of growing season in 2000. Photosynthesis and ecosystem respiration calculated by TCBM were −490gCO₂ m^-2 and 156 gCO₂m^-2, respectively. The larger photosynthesis and lower respiration were brought about because of the high water level condition, with standing water completely submerging the base of the wet sedge tundra. These conditions provided high photosynthetic activity and less gases-exchange between rhizosphere and atmosphere.