Annals of Botany 85: 317-323, 2000
© 2000 Annals of Botany Company
Growth Responses of Common Ash Seedlings (Fraxinus excelsior L.) to Total and Partial Defoliation
Laboratoire de Biologie et Ecophysiologie, Institut des Sciences et des Techniques de l'Environnement, Université de Franche-Comté, Place Leclerc, F-25030, Besançon cedex, France Laboratoire de Biologie et Ecophysiologie, Institut des Sciences et des Techniques de l'Environnement, Université de Franche-Comté, Pôle Universitaire, BP 71427, F-25211, Montbéliard cedex, France
Received: 12 July 1999 ; Returned for revision: 2 September 1999 . Accepted: 5 November 1999
Common ash seedlings, grown in controlled conditions, were completely defoliated 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 d after the completion of stem elongation. Complete defoliation up to 80 d after the completion of stem elongation caused renewed growth of terminal buds. The buds had changed from a reversible state to an irreversible state by 80 d after the cessation of stem elongation, as shown by the lack of response to defoliation. When leaves were removed before the cessation of stem elongation, rather than after, a similar enhancement of stem growth was observed. Partial defoliation experiments indicated that the degree and location of defoliation play important roles in the plant response. Complete defoliation or complete removal of leaflets was necessary to obtain 100% budburst. Apical dominance was altered by partial defoliation treatments such that the basal axillary buds began to grow out. Partial defoliation, especially before the cessation of stem elongation, was prejudicial to stem elongation. These results suggest that the induction of compensatory growth mechanisms in ash seedlings require a threshold level of defoliation. Copyright 2000 Annals of Botany Company
Fraxinus excelsior L., common ash, defoliation, growth, paradormancy