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Title: How do leaf hydraulics limit stomatal conductance at high water vapour pressure deficits?

item Bunce, James

Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/2006
Publication Date: 6/2/2006
Citation: Bunce, J.A. 2006. How do leaf hydraulics limit stomatal conductance at high water vapour pressure deficits? Plant Cell and Environment. 29:1644-1650.

Interpretive Summary: Global warming may result in hotter and drier conditions for growing plants on which we depend for food. We carried out this study to learn more about why plants do not grow as well under hot, dry conditions. We found that growth is reduced because plants leaves become overly sensitive to carbon dioxide in the air, and don't let as much carbon dioxide into the leaf where it can be converted to sugars that eventually become food. This information may help scientists develop plants that can still grow well even when it is hot and dry, by making them less sensitive to carbon dioxide.

Technical Abstract: A reduction in leaf stomatal conductance with increasing leaf to air difference in water vapor pressure (D) is nearly ubiquitous. Ecological comparisons of sensitivity have led to the hypothesis that the reduction in stomatal conductance with increasing D serves to limit transpiration and maintains leaf water potentials above those which would cause cavitation of xylem and loss of hydraulic conductance. Further, reduction in leaf water potential is commonly hypothesized to be the proximate signal which limits stomatal conductance at high D. Both hypotheses were tested by exposing Abutilon theophrasti, Glycine max, Gossypium hirsutum, and Xanthium strumarium to D high enough to reduce stomatal conductance and then decreasing the ambient carbon dioxide concentration, and observing the resulting changes in stomatal conductance, transpiration rate and leaf water potential, and their reversibility. Regardless of whether the treatments were applied to leaves or whole shoots, reducing the carbon dioxide concentration at high D increased stomatal conductance and transpiration rate and lowered leaf water potential. Maintaining the high transpiration rates for as long as an hour did not result in reductions in hydraulic conductance or stomatal conductance. The results indicate that low leaf water potential did not limit stomatal conductance at high D and that even lower leaf water potentials did not cause a reduction in hydraulic conductance. Reduced stomatal conductance at high D in these species resulted at least partly from increased stomatal sensitivity to carbon dioxide concentration at high D.