The Seasonal Course of Aboveground Production and Chlorophyll Distribution in a Wet Arctic Tundra at Barrow, Alaska

Tieszen, L

The seasonal changes in dry weight and chlorophyll content of each species were documented in a tundra community at Barrow, Alaska. Aboveground production of 102 g m2 dry matter was attained 55 days subsequent to growth initiation and was accounted for mainly by three monocotyledons, Dupontia fischeri, Carex aquatilis, and Eriophorum angustifolium. Maximum chlorophyll standing crops and concentrations were observed earlier than maximum dry weight suggesting that senescence was initiated before peak production was attained. There was no relationship between maximum chlorophyll concentration and dry matter production although the species revealed different patterns in chlorophyll production and loss. Dicotyledons generally possessed higher early season chlorophyll concentrations. Evidence is presented which suggests a greater turnover of photosynthetic structures in some monocotyledons than in dicotyledons. Dicotyledons generally possessed more horizontal leaves and were positioned in the lower part of the canopy whereas the dominant grasses and sedges formed the upper parts of the canopy. Nearly all species possessed significant amounts of chlorophyll in nonblade structures. The interpretations of the pigment and production data suggest that photosynthesis with positive net CO2 uptake should be initiated very soon after snowmelt, especially in most monocotyledons. Leaf photosynthetic efficiency should be greatest during or shortly after the time of leaf expansion and near the summer solstice, whereas whole community photosynthesis might be greatest around July 25 which is near the period of peak standing crop of chlorophyll. It is suggested that substantial CO2 uptake may occur in August and early September even though there is no net increase in aboveground dry matter. The potential adaptive significance of different seasonal and growth patterns are discussed.

The Seasonal Course of Aboveground Production and Chlorophyll Distribution in a Wet Arctic Tundra at Barrow, Alaska

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