Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 12, 2000
Publication Date: N/A
Interpretive Summary: The rising concentration of carbon dioxide in the atmosphere reduces the aperture of stomatal pores on leaves, which control the rate of water loss from plants. A reduction in the rate of water loss from plant leaves would have an important effect on climate, by reducing evaporative cooling. To accurately predict future climates, it is important to quantify the reduction in aperture of stomatal pores which would result from increased atmospheric carbon dioxide. Two different causes of reduced pore aperture at elevated carbon dioxide are known to occur, but have not been separately quantified for crops plants grown in the field. The two causes are a direct effect of elevated carbon dioxide on stomatal aperture and an effect of long-term exposure to elevated carbon dioxide, termed acclimation. In this research, we have separated the direct and acclimatory responses for four species of crop plants. While prior work has assumed that the main effect of rising atmospheric carbon dioxide on stomatal aperture would be the direct effect, these results indicated that this was true for only one of the four species studied. For the other three species, the acclimatory effect was more important. In two of the species, the acclimation of stomatal aperture was related to adjustments in the photosynthetic system caused by long-term growth at elevated carbon dioxide, but in the third species there was no change in photosynthetic characteristics. This work will aid climate modelers forecasting the effects on climate of rising atmospheric carbon dioxide.
In order to separate the net effect of growth at elevated carbon dioxide on stomatal conductance into direct and acclimatory responses, we measured midday values of stomatal conductance for plants grown in field plots in open topped chambers at 350 and 700 ppm carbon dioxide for winter wheat, winter barley, potato, and sorghum. The acclimatory response was determined by comparing stomatal conductances measured at 700 ppm for plants grown at both concentations. The direct effect of increasing carbon dioxide from 350 to 700 ppm was determined for plants grown at the lower concentation. For all species the effect of growth carbon dioxide was significant for stomatal conductances measured at 700 ppm, with lower conductance for plants grown at the elevated carbon dioxide. The magnitude of stomatal acclimation was larger for all species on days with low leaf to oair water vapor pressure difference. For barley, there was no other evidence for stomatal acclimation, despite consistent down-regulation of assimilation rate in plants grown at elevated carbon dioxide. In wheat and potato, the magnitude of stomatal acclimation varied in proportion to the magnitude of down-regulation of assimilation rate through the season. In sorghum, stomatal conductance consistently exhibited acclimation beyond the vapor pressure difference effect, but there was no down-regulation of assimilation rate. In none of the species, except barley, was the direct effect the larger component of the net reduction in stomatal conductance.