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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

Authors

  • SANDRA J. BUCCI,

    Corresponding author
    1. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina
    2. Grupo de Estudios Biofísicos y Eco-fisiológicos (GEBEF), Departamento de Biología, Facultad de Ciencias Naturales, Universidad Nacional de la Patagonia San Juan Bosco, Comodoro Rivadavia, Argentina
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  • FABIAN G. SCHOLZ,

    1. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina
    2. Grupo de Estudios Biofísicos y Eco-fisiológicos (GEBEF), Departamento de Biología, Facultad de Ciencias Naturales, Universidad Nacional de la Patagonia San Juan Bosco, Comodoro Rivadavia, Argentina
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  • MARIA LAURA PESCHIUTTA,

    1. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina
    2. Grupo de Estudios Biofísicos y Eco-fisiológicos (GEBEF), Departamento de Biología, Facultad de Ciencias Naturales, Universidad Nacional de la Patagonia San Juan Bosco, Comodoro Rivadavia, Argentina
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  • NADIA S. ARIAS,

    1. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina
    2. Grupo de Estudios Biofísicos y Eco-fisiológicos (GEBEF), Departamento de Biología, Facultad de Ciencias Naturales, Universidad Nacional de la Patagonia San Juan Bosco, Comodoro Rivadavia, Argentina
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  • FREDERICK C. MEINZER,

    1. USDA Forest Service, Forestry Sciences Laboratory, Corvallis, OR, USA
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  • GUILLERMO GOLDSTEIN

    1. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina
    2. Laboratorio de Ecología Funcional (LEF), Departamento de Ecología, Genética y Evolución, FCEyN, Universidad de Buenos Aires, Buenos Aires, Argentina
    3. University of Miami, Department of Biology, Coral Gables, FL, USA
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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% (ΨΨ50), 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.

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