© 1998 Heron Publishing—Victoria, Canada
Stomatal conductance, growth and root signaling in Betula pendula seedlings subjected to partial soil drying
C. Fort (1), F. Muller (1, 2), P. Label (2), A. Granier (1) and E. Dreyer (1, 3)
1. Équipe Bioclimatologie et Ecophysiologie, Unité d'Ecophysiologie Forestière, INRA Nancy, F-54280 Champenoux, France / 2. Unité Physiologie du Développement, Laboratoire d'Amélioration des Arbres Forestiers, INRA Orléans, F-45160 Olivet, France / 3. Author to whom correspondence should be addressed (Dreyer@nancy.inra.fr) / Received January 7, 1998
Summary
Seedlings of Betula pendula Roth were grown with their root systems separated between two soil compartments. Four treatments were imposed: (i) adequate
irrigation in both compartments (WW, controls); (ii) adequate irrigation in one compartment and drought in the other compartment
(WD); (iii) drought in both compartments (DD); and (iv) half of the root system severed and the remainder kept well-watered
(root excision, RE). Predawn leaf water potential, stomatal conductance, soil-to-leaf specific hydraulic conductance, and
root and leaf growth decreased in DD-treated seedlings, which also displayed severe leaf shedding (30% loss in leaf area).
The DD treatment also resulted in increased concentrations of abscisic acid (ABA) and its glucose ester in the xylem sap of
roots and shoots compared to concentrations in control seedlings (about 200 versus 20 nM). Despite the difference in xylem
sap concentrations, total ABA flux to the shoots was similar in the two treatments (1–2 pmol ABA m–2 leaf area s–1) as a result of reduced transpiration in the DD-treated seedlings. Compared with root growth in control plants, root growth
increased in the RE-treated plants and decreased in the drying compartment of the WD treatment; however, the RE and WD treatments
only slightly reduced leaf expansion, and had no detectable effects on shoot water relations or ABA concentrations of the
root and shoot xylem sap. We conclude that short-term soil water depletion affecting only 50% of the root system does not
cause a measurable stress response in birch shoots, despite root growth cessation in the fraction of drying soil.
Keywords:
abscisic acid, birch, water stress, xylem sap.
