Response of Eriophorum Vaginatum to Elevated CO_2 and Temperature in the Alaskan Tussock Tundra

Abstract

Small greenhouses were used in the arctic to maintain Erioporum vaginatum—dominated tussock tundra for 10 wk at ambient CO₂ (340 μL/L), elevated CO₂ (510 or 680 μL/L), or elevated CO₂ and 4°C above ambient temperature (680 μL/L, ambient + 4°). These treatments represent present levels of atmospheric CO₂ and temperature, and those predicted for the next century. Within 3 wk, plants maintained at elevated CO₂ exhibited a physiological adjustment of their photosynthetic rate so that plants grown at ambient and elevated CO₂ levels had similar photosynthetic rates at their respective growth CO₂ concentrations. The reduction in photosynthetic capacity for plants grown at elevated CO₂ levels did not appear to be due to stomatal closure or end—product inhibition. Other possible mechanisms were not explored. Transpiration rates and water use efficiency did not differ among treatments in the generally wet environment of tussock tundra. Relative leaf growth rate and the seasonal pattern of growth were also unaltered, suggesting that the growth of mature tillers is not, under normal ambient conditions, limited by temperature or carbohydrate. However, new tiller production was significantly increased at elevated CO₂, suggesting that the long—term effect of CO₂ enhancement in this sedge may be the production of a greater number of new tillers rather than an increase in the size or productivity of existing tillers. Our results are consistent with the notion that growth of Eriophorum vaginatum in the field is more limited by nutrient supply than by photosynthesis. We further suggest that photosynthetic rates reflect the sink activity. It is therefore very difficult to assign cause and effect between growth rates and photosynthetic rates.