Increasing leaf hydraulic conductance with transpiration rate minimizes the water potential drawdown from stem to leaf.
Leaf hydraulic conductance (k leaf) is a central element in the regulation of leaf water balance but the properties of k leaf remain uncertain. Here, the evidence for the following two models for k leaf in well-hydrated plants is evaluated: (i) k leaf is constant or (ii) k leaf increases as transpiration rate (E) increases. The difference between stem and leaf water potential (ΔΨstem-leaf), stomatal conductance (g s), k leaf, and E over a diurnal cycle for three angiosperm and gymnosperm tree species growing in a common garden, and for Helianthus annuus plants grown under sub-ambient, ambient, and elevated atmospheric CO₂ concentration were evaluated. Results show that for well-watered plants k leaf is positively dependent on E. Here, this property is termed the dynamic conductance, k leaf(E), which incorporates the inherent k leaf at zero E, which is distinguished as the static conductance, k leaf(0). Growth under different CO₂ concentrations maintained the same relationship between k leaf and E, resulting in similar k leaf(0), while operating along different regions of the curve owing to the influence of CO₂ on g s. The positive relationship between k leaf and E minimized variation in ΔΨstem-leaf. This enables leaves to minimize variation in Ψleaf and maximize g s and CO₂ assimilation rate over the diurnal course of evaporative demand.
['Simonin|Kevin A|KA|', 'Burns|Emily|E|', 'Choat|Brendan|B|', 'Barbour|Margaret M|MM|', 'Dawson|Todd E|TE|', 'Franks|Peter J|PJ|']
D001692:Biological Transport D006368:Helianthus D007700:Kinetics D018515:Plant Leaves D018547:Plant Stems D018526:Plant Transpiration D014867:Water
Leaf hydraulic conductance transpiration leaf water potential stomatal conductance stem water potential water relations.