title: The stem xylem of Patagonian shrubs operates far from the point of catastrophic dysfunction and is additionally protected from drought-induced embolism by leaves and roots.
abstract: Hydraulic architecture was studied in shrub species differing in rooting depth in a cold desert in Southern Argentina. All species exhibited strong hydraulic segmentation between leaves, stems and roots with leaves being the most vulnerable part of the hydraulic pathway. Two types of safety margins describing the degree of conservation of the hydraulic integrity were used: the difference between minimum stem or leaf water potential (Ψ) and the Ψ at which stem or leaf hydraulic function was reduced by 50% (Ψ - Ψ50), and the difference between leaf and stem Ψ50. Leaf Ψ50 - stem Ψ50 increased with decreasing rooting depth. Large diurnal decreases in root-specific hydraulic conductivity suggested high root vulnerability to embolism across all species. Although stem Ψ50 became more negative with decreasing species-specific Ψsoil and minimum stem Ψ, leaf Ψ50 was independent of Ψ and minimum leaf Ψ. Species with embolism-resistant stems also had higher maximum stem hydraulic conductivity. Safety margins for stems were >2.1 MPa, whereas those for leaves were negative or only slightly positive. Leaves acted as safety valves to protect the integrity of the upstream hydraulic pathway, whereas embolism in lateral roots may help to decouple portions of the plant from the impact of drier soil layers.
authors: Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), 1917, Buenos Aires, Argentina; Grupo de Estudios Biofísicos y Eco-fisiológicos (GEBEF), Departamento de Biología, Facultad de Ciencias Naturales, Universidad Nacional de la Patagonia San Juan Bosco, 9000, Comodoro Rivadavia, Argentina.
authors: Sandra J
authors: SJ
authors: Bucci
authors: Fabian G
authors: FG
authors: Scholz
authors: Maria Laura
authors: ML
authors: Peschiutta
authors: Nadia S
authors: NS
authors: Arias
authors: Frederick C
authors: FC
authors: Meinzer
authors: Guillermo
authors: G
authors: Goldstein
mesh_terms: D001118:Argentina; D002940:Circadian Rhythm / Q000502:physiology; D055864:Droughts; D018515:Plant Leaves / Q000502:physiology*; D018521:Plant Physiological Phenomena; D018517:Plant Roots / Q000502:physiology*; D018547:Plant Stems / Q000502:physiology*; D014867:Water; D052584:Xylem / Q000502:physiology*
chemical_list: D014867:Water
keywords: hydraulic conductivity; hydraulic segmentation; leaf water potential; safety margin