Short-Term Effects of CO(2) on Gas Exchange of Leaves of Bigtooth Aspen (Populus grandidentata) in the Field.

The short term effects of increased levels of CO(2) on gas exchange of leaves of bigtooth aspen (Populus grandidentata Michx.) were studied at the University of Michigan Biological Station, Pellston, MI. Leaf gas exchange was measured in situ in the upper half of the canopy, 12 to 14 meters above ground. In 1900 microliters per liter CO(2), maximum CO(2) exchange rate (CER) in saturating light was increased by 151% relative to CER in 320 microliters per liter CO(2). The temperature optimum for CER shifted from 25 degrees C in 320 microliters per liter CO(2) to 37 degrees C in 1900 microliters per liter CO(2). In saturating light, increasing CO(2) level over the range 60 to 1900 microliters per liter increased CER, decreased stomatal conductance, and increased leaf water use efficiency. The initial slope of the CO(2) response curve of CER was not significantly different at 20 and 30 degrees C leaf temperatures, although the slope did decline significantly during leaf senescence. In 1900 microliters per liter CO(2), CER increased with increasing light. The light saturation point and maximum CER were higher in 30 degrees C than in 20 degrees C, although there was little effect of temperature in low light. The experimental results are consistent with patterns seen in laboratory studies of other C(3) species and define the parameters required by some models of aspen CER in the field.