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Forced depression of leaf hydraulic conductance in situ : effects on the leaf gas exchange of forest trees


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Brodribb, TJ 2007 , 'Forced depression of leaf hydraulic conductance in situ : effects on the leaf gas exchange of forest trees' , Functional Ecology, vol. 21, no. 4 , pp. 705-712 , doi: 10.1111/j.1365-2435.2007.01271.x.

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1. Recent work on the hydraulic conductance of leaves suggests that maximum photosynthetic performance of a leaf is defined largely by its plumbing. Pursuing this idea, we tested how the diurnal course of gas exchange of trees in a dry tropical forest was affected by artificially depressing the hydraulic conductance of leaves (Kleaf).

2. Individual leaves from four tropical tree species were exposed to a brief episode of forced evaporation by blowing warm air over leaves in situ. Despite humid soil and atmospheric conditions, this caused leaf water potential (Ψleaf) to fall sufficiently to induce a 50–74% drop in Kleaf.

3. Two of the species sampled proved highly sensitive to artificially depressed Kleaf, leading to a marked and sustained decline in the instantaneous rate of CO2 uptake, stomatal conductance and transpiration. Leaves of these species showed a depression of hydraulic and photosynthetic capacity in response to the ‘blow-dry’ treatment similar to that observed when major veins in the leaf were severed.

4. By contrast, the other two species sampled were relatively insensitive to Kleaf manipulation; photosynthetic rates were indistinguishable from control (untreated) leaves 4 h after treatment. These insensitive species demonstrate a linear decline of Kleaf with Ψleaf, while Kleaf in the two sensitive species falls precipitously at a critical water deficit.

5. We propose that a sigmoidal Kleaf vulnerability enables a high diurnal yield of CO2 at the cost of exposing leaves to the possibility of xylem cavitation. Linear Kleaf vulnerability leads to a relatively lower CO2 yield, while providing better protection against cavitation.

Item Type: Article
Authors/Creators:Brodribb, TJ
Keywords: dry tropics, leaf hydraulics, photosynthetic depression, cavitation, diurnal, assimilation
Journal or Publication Title: Functional Ecology
ISSN: 0269-8463
DOI / ID Number: 10.1111/j.1365-2435.2007.01271.x
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