title: Increasing leaf hydraulic conductance with transpiration rate minimizes the water potential drawdown from stem to leaf.
abstract: 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.
authors.affiliation: Department of Biology, San Francisco State University, San Francisco, CA 94132, USA simonin@sfsu.edu.
authors.forename: Kevin A
authors.initials: KA
authors.lastname: Simonin
authors.affiliation: Save The Redwoods League, 111 Sutter Street, 11th Floor, San Francisco, CA 94104, USA.
authors.forename: Emily
authors.initials: E
authors.lastname: Burns
authors.affiliation: University of Western Sydney, Hawkesbury Institute for the Environment, Locked Bag 1797, Penrith 2751, NSW, Australia.
authors.forename: Brendan
authors.initials: B
authors.lastname: Choat
authors.affiliation: Faculty of Agriculture and Environment, University of Sydney, NSW 2006, Australia.
authors.forename: Margaret M
authors.initials: MM
authors.lastname: Barbour
authors.affiliation: Department of Integrative Biology, University of California-Berkeley, Berkeley, CA 94720, USA.
authors.forename: Todd E
authors.initials: TE
authors.lastname: Dawson
authors.affiliation: Faculty of Agriculture and Environment, University of Sydney, NSW 2006, Australia.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Franks
mesh_terms: D001692:Biological Transport; D006368:Helianthus / Q000737:chemistry / Q000502:physiology*; D007700:Kinetics; D018515:Plant Leaves / Q000737:chemistry / Q000502:physiology*; D018547:Plant Stems / Q000737:chemistry / Q000502:physiology*; D018526:Plant Transpiration; D014867:Water / Q000737:chemistry / Q000378:metabolism*
chemical_list: D014867:Water
keywords: Leaf hydraulic conductance; leaf water potential; stem water potential; stomatal conductance; transpiration; water relations.