Interpretation of seasonal changes of xylem embolism and plant hydraulic resistance in Fagus sylvatica

Authors

  • F. MAGNANI,

    Corresponding author
    1. Istituto Miglioramento Genetico delle Piante Forestali, Consiglio Nazionale delle Ricerche, via A. Vannucci 13, 50134 Firenze, Italy
      and present address: F. Magnani, Institute of Ecology and Resource Management, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh EH93JU, UK.
    Search for more papers by this author
  • M. BORGHETTI

    1. Dipartimento di Produzione Vegetale, Università della Basilicata, via N. Sauro 85, 85100 Potenza, Italy
    Search for more papers by this author

and present address: F. Magnani, Institute of Ecology and Resource Management, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh EH93JU, UK.

ABSTRACT

The annual course of xylem embolism in twigs of adult beech trees was monitored, and compared to concurrent changes of tree water status and hydraulic resistances. Xylem embolism was quantified in 1-year-old apical twigs by the hydraulic conductivity as a percentage of the maximum measured after removal of air emboli. Tree and root hydraulic resistances were estimated from water potential differences and sap flux measurements. The considerable degree of twig embolism found in winter (up to 90% loss of hydraulic conductivity) may be attributed to the effect of freeze-thaw cycles in the xylem. A partial recovery from winter embolism occurred in spring, probably because of the production of new functional xylem. Xylem embolism fluctuated around 50% throughout the summer, without significant changes. Almost complete refilling of apical twigs was observed early in autumn. A significant negative correlation was found between xylem embolism and precipitation; thus, an active role of rainfall in embolism reversion is hypothesized. Tree and root hydraulic resistances were found to change throughout the growing period. A marked decrease of hydraulic resistance preceded the refilling of apical twigs in the autumn. Most of the decrease in total tree resistance was estimated to be located in the root compartment.

Ancillary