Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

There is general agreement that in many regions additional precipitation with climate change will not be able to balance the increased evaporation rate induced by higher air temperatures, causing periods of intense drought. Although seedlings of Abies balsamea growing in the boreal forest are known for their resistance to harsh environmental conditions, the impact of water stress on their growth still remains largely unexamined. The aim of this study was to investigate growth responses of this species during and after a dry period by monitoring cambial and apical meristem activity at short time scale. Meristem growth was studied from May to October 2005 on seedlings of A. balsamea submitted to a 20-day-long dry period in June-July. Lower rates of shoot lengthening were observed in non-irrigated seedlings only in the first part of the growing season. Irrigated and non-irrigated trees showed the same trend of xylem formation and timings of cell differentiation. Cell production during cambial activity was estimated at about one xylem cell per day thus achieving in 100 days 108 tracheids in the tree ring and a width of 2 mm, with thinner tree rings observed in non-irrigated plants. A reduction of up to 50% in lumen area and cell diameter was observed for the cells produced during the dry period. Response of A. balsamea seedlings to a 20-day-long dry period consisted of good resistance of the cambial meristems during and after water stress, high sensitivity and rapid recovery of cell sizes during water depletion and slow but effective recovery of shoot growth after treatment.