Diurnal and seasonal variation in root xylem embolism in neotropical savanna woody species: impact on stomatal control of plant water status

Authors

  • J-C. DOMEC,

    Corresponding author
    1. Department of Wood Science and Engineering, Oregon State University, Corvallis, OR 97331, USA
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  • F. G. SCHOLZ,

    1. Laboratorio de Ecología Funcional, Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Nuñez, Buenos Aires, Argentina
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  • S. J. BUCCI,

    1. Laboratorio de Ecología Funcional, Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Nuñez, Buenos Aires, Argentina
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  • F. C. MEINZER,

    1. USDA Forest Service, Forestry Sciences Laboratory, 3200 SW Jefferson Way, Corvallis, OR 97331, USA
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  • G. GOLDSTEIN,

    1. Laboratorio de Ecología Funcional, Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Nuñez, Buenos Aires, Argentina
    2. Department of Biology, University of Miami, Coral Gables, FL 33124, USA
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  • R. VILLALOBOS-VEGA

    1. Department of Biology, University of Miami, Coral Gables, FL 33124, USA
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Jean-Christophe Domec. Fax: + 1 541 737 3385; e-mail: jc.domec@oregonstate.edu

ABSTRACT

Vulnerability to water-stress-induced embolism and variation in the degree of native embolism were measured in lateral roots of four co-occurring neotropical savanna tree species. Root embolism varied diurnally and seasonally. Late in the dry season, loss of root xylem conductivity reached 80% in the afternoon when root water potential (Ψroot) was about −2.6 MPa, and recovered to 25–40% loss of conductivity in the morning when Ψroot was about −1.0 MPa. Daily variation in Ψroot decreased, and root xylem vulnerability and capacitance increased with rooting depth. However, all species experienced seasonal minimum Ψroot close to complete hydraulic failure independent of their rooting depth or resistance to embolism. Predawn Ψroot was  lower  than  Ψsoil when  Ψsoil was  relatively  high  (>−0.7 MPa) but became less negative than Ψsoil later in the dry season, consistent with a transition from a disequilibrium between plant and soil Ψ induced by nocturnal transpiration to one induced by hydraulic redistribution of water from deeper soil layers. Shallow longitudinal root incisions external to the xylem prevented reversal of embolism overnight, suggesting that root mechanical integrity was necessary for recovery, consistent with the hypothesis that if embolism is a function of tension, refilling may be a function of internal pressure imbalances. All species shared a common relationship in which maximum daily stomatal conductance declined linearly with increasing afternoon loss of root conductivity over the course of the dry season. Daily embolism and refilling in roots is a common occurrence and thus may be an inherent component of a hydraulic signaling mechanism enabling stomata to maintain the integrity of the hydraulic pipeline in long-lived structures such as stems.

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