Threshold response of mesophyll CO2conductance to leaf hydraulics in highly transpiring hybrid poplar clones exposed to soil drying

Mesophyll conductance (g m ) has been shown to impose significant limitations to net CO 2 assimilation (A) in various species during water stress. Net CO 2 assimilation is also limited by stomatal conductance to water (g sw ), both having been shown to co-vary with leaf hydraulic conductance (K leaf...

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Bibliographic Details
Published in:Journal of experimental botany 2014-01, Vol.65 (2), p.741-753
Main Authors: Théroux-Rancourt, Guillaume, Éthier, Gilbert, Pepin, Steeve
Format: Article
Language:English
Subjects:
Calibration
Dehydration
Drought
Estimation methods
Hydraulics
Mesophyll
Mesophyll cells
Photosynthesis
Plant cells
RESEARCH PAPER
Vascular plants
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Summary:Mesophyll conductance (g m ) has been shown to impose significant limitations to net CO 2 assimilation (A) in various species during water stress. Net CO 2 assimilation is also limited by stomatal conductance to water (g sw ), both having been shown to co-vary with leaf hydraulic conductance (K leaf ). Lately, several studies have suggested a close functional link between K leaf , g sw , and g m . However, such relationships could only be circumstantial since a recent study has shown that the response of g m to drought could merely be an artefactual consequence of a reduced intercellular CO 2 mole fraction (C i ). Experiments were conducted on 8-week-old hybrid poplar cuttings to determine the relationship between K leaf , g sw , and g m in clones of contrasting drought tolerance. It was hypothesized that changes in g sw and K leaf in response to drought would not impact on g m over most of its range. The results show that K leaf decreased in concert with g sw as drought proceeded, whereas g m measured at a normalized C i remained relatively constant up to a g sw threshold of ∼0.15 mol m -2 s -1 . This delayed gm response prevented a substantial decline in A at the early stage of the drought, thereby enhancing water use efficiency. Reducing the stomatal limitation of droughted plants by diminishing the ambient CO 2 concentration of the air did not modify g m or K leaf . The relationship between gas exchange and leaf hydraulics was similar in both drought-tolerant and drought-sensitive clones despite their contrasting vulnerability to stem cavitation and stomatal response to soil drying. The results support the hypothesis of a partial hydraulic isolation of the mesophyll from the main transpiration pathway.
ISSN:0022-0957
1460-2431