Direct effect of elevated CO(2) on nocturnal in situ leaf respiration in nine temperate deciduous tree species is small.

Direct (i.e., short-term) effects of elevated CO(2) on nocturnal in situ leaf respiration rate were measured in nine deciduous tree species (seven genera) in 20 3.5-4.0-h experiments. During the experiments, CO(2) concentration was alternated between 400 and 800 ppm (approximately 40 and 80 Pa of CO(2)). Data analysis accounted for effects on respiration rate of the normal decline in temperature with time after sunset. The median response to a 40-Pa increase in CO(2) was a 1.5% decrease in respiration rate, with responses ranging from a 5.6% inhibition to a 0.4% stimulation. Direct effects of elevated CO(2) on respiration were similar among the species. Thus, the response of nocturnal leaf respiration rate to a short-term CO(2) increase was small, and of little practical importance to the accuracy of measurements of respiration involving similar changes in CO(2) concentration during measurement. These direct respiratory responses of leaves to elevated CO(2) would translate into only slight, if any, effects on the carbon balance of temperate deciduous forests in a future atmosphere containing as much as 80 Pa CO(2).