Hydraulic limits on maximum plant transpiration and the emergence of the safety-efficiency trade-off.
Soil and plant hydraulics constrain ecosystem productivity by setting physical limits to water transport and hence carbon uptake by leaves. While more negative xylem water potentials provide a larger driving force for water transport, they also cause cavitation that limits hydraulic conductivity. An optimum balance between driving force and cavitation occurs at intermediate water potentials, thus defining the maximum transpiration rate the xylem can sustain (denoted as E(max)). The presence of this maximum raises the question as to whether plants regulate transpiration through stomata to function near E(max). To address this question, we calculated E(max) across plant functional types and climates using a hydraulic model and a global database of plant hydraulic traits. The predicted E(max) compared well with measured peak transpiration across plant sizes and growth conditions (R = 0.86, P < 0.001) and was relatively conserved among plant types (for a given plant size), while increasing across climates following the atmospheric evaporative demand. The fact that E(max) was roughly conserved across plant types and scales with the product of xylem saturated conductivity and water potential at 50% cavitation was used here to explain the safety-efficiency trade-off in plant xylem. Stomatal conductance allows maximum transpiration rates despite partial cavitation in the xylem thereby suggesting coordination between stomatal regulation and xylem hydraulic characteristics.
Department of Civil and Environmental Engineering, Duke University, Box 90287, Durham, NC, 27708-0287, USA.|Nicholas School of the Environment, Duke University, Box 90328, Durham, NC, 27708, USA.
Stefano
S
Manzoni
Department of Crop Production Ecology, Swedish University of Agricultural Sciences, Box 7043, SE-750 07, Uppsala, Sweden.
Giulia
G
Vico
Department of Civil and Environmental Engineering, Duke University, Box 90287, Durham, NC, 27708-0287, USA.|Nicholas School of the Environment, Duke University, Box 90328, Durham, NC, 27708, USA.
Gabriel
G
Katul
Nicholas School of the Environment, Duke University, Box 90328, Durham, NC, 27708, USA.|Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83, Umeå, Sweden.
Sari
S
Palmroth
Nicholas School of the Environment, Duke University, Box 90328, Durham, NC, 27708, USA.|Department of Biology, Duke University, Box 90338, Durham, NC, 27708, USA.
Robert B
RB
Jackson
Department of Civil and Environmental Engineering, Duke University, Box 90287, Durham, NC, 27708-0287, USA.|Nicholas School of the Environment, Duke University, Box 90328, Durham, NC, 27708, USA.
Amilcare
A
Porporato
D002980:Climate; D008954:Models, Biological; D018526:Plant Transpiration / Q000502:physiology*; D014867:Water / Q000502:physiology*; D052584:Xylem / Q000502:physiology
D014867:Water