Beech (<i>Fagus sylvatica</i> L.) branches show acclimation of xylem anatomy andhydraulic properties to increased light after thinning

Abstract

Hydraulic acclimation of Fagus sylvatica L. was analysed in response to forest thinning. Several months after thinning, leaf and xylem water potential and stomatal conductance of thinned branches were compared to sun-exposed and shade branches. We characterised vulnerability to cavitation for branches taken from these three treatments. We compared effect of thinning on xylem anatomy (mean vessel diameter, vessel density). Thinned branches exhibited higher stomatal conductance and lower leaf water potential. These results were well correlated with vulnerability to cavitation. Thinned branches were less vulnerable than shade branches and mean vessel diameter and vessel density increased in thinned branches. These differences showed a partial hydraulic acclimation to climate changes. We confirmed that vulnerability to cavitation and xylem anatomy in Fagus sylvatica acclimate to changing light conditions, and we concluded that hydraulic architecture acclimates sufficiently fast after environmental changes to protect xylem from dysfunction while maintaining open stomata. Fagus sylvatica L. / thinning / xylem embolism / xylem anatomy / light acclimation Rsum -Acclimatation anatomique et hydraulique du xylme aprs une claircie chez le htre (Fagus sylvatica L.). Nous avons analys l'acclimatation hydraulique de htre Fagus sylvatica L. suite une claircie forestire. Quelques mois aprs l'claircie, nous avons mesur le potentiel hydrique des feuilles et du xylme et la conductance stomatique de branches claircies et compar ces rsultats des branches de lumire et d'ombre. Nous avons dtermin la vulnrabilit la cavitation de ces branches et caractris leurs diffrences morphologiques et anatomiques. Les branches claircies ont prsent des conductances stomatiques plus fortes et des potentiels hydriques foliaires plus ngatifs que les autres branches. Ces branches prsentaient une vulnrabilit la cavitation plus faible que les branches d'ombre et des vaisseaux plus gros et plus nombreux. Ces rsultats montrent une acclimatation hydraulique partielle mais suffisamment rapide pour protger le xylme de dysfonctionnement et confirment que la vulnrabilit la cavitation chez le htre dpend fortement des conditions lumineuses.