The refilling of embolized xylem in Pinus sylvestris L.

Authors

  • M. BORGHETTI,

    Corresponding author
    1. Istituto Miglioramento Genetico delle Piante Forestall, Consiglio Nazionale delle Ricerche, via S. Bonaventura 13, 50145 Firenze, Italy
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  • W. R. N. EDWARDS,

    1. Department of Scientific and Industrial Research, Division of Fruit and Trees, Private Bag, Palmerston North, New Zealand
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  • J. GRACE,

    1. Institute of Ecology and Resource Management, University of Edinburgh, The King's Buildings, Mayfield Road, Edinburgh EH9 3JU, Scotland
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  • P. G. JARVIS,

    1. Institute of Ecology and Resource Management, University of Edinburgh, The King's Buildings, Mayfield Road, Edinburgh EH9 3JU, Scotland
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  • A. RASCHI

    1. Istituto di Analisi ambientale e Telerilevamento applicati all'Agricoltura, Consiglio Nazionale delle Ricerche, P. le delle Cascine 18, 50144 Firenze, Italy
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M. Borghetti, Istituto Miglioramento Genetico delle Piante Forestali, Comsiglio Nazionale delle Ricerche, via S. Bonaventura 13. 50145 Firenze, Italy.

Abstract

Abstract. The hypothesis that ray parenchyma cells are actively involved in the refilling of embolized xylem of Pinus sylvestris L. was tested by killing the ray parenchyma and comparing rehydration of killed stems with that of control material. Killing of ray parenchyma was achieved using hot water or sodium azide. In most experiments, the available water for refilling was at negative water potential. Experiments were done on three kinds of plant material: small branch segments, potted seedlings and small potted trees. In all experiments, there was no indication that the azide-killed xylem was slower to refill than the control material and it was concluded that the parenchyma has no role in the refilling process, which therefore must be purely physical or physicochemical. Stems treated with hot water did not refill; we suggest that this may be caused by high temperatures decreasing the water permeability of the tracheid wall. The refilling of small branch segments may be explained by surface tension forces (capillary action), which inside the tracheid lumen may lower the water potential down to -9.7kPa; this may be enough to draw in water from the available water that in experiment one was at -2kPa. In the case of seedlings or saplings, capillary action cannot explain refilling, because the xylem water potentials were always lower than those estimated from tracheid radii. Condensation of water during diurnal cycles of warming and cooling is also unlikely to contribute to refilling significantly. To account for refilling in these cases, it is supposed that the tracheid wall may be chemically active and able to lower the water potential below the value expected by capillarity.

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