Tree Physiology Advance Access originally published online on September 10, 2009
Tree Physiology 2009 29(11):1395-1405; doi:10.1093/treephys/tpp067
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Hydraulic properties of naturally regenerated beech saplings respond to canopy opening
1 INRA, UMR 1137 Ecologie et Ecophysiologie Forestières, F-54280 Champenoux, France
2 Nancy Université, Université Henri Poincaré, UMR 1137 Ecologie et Ecophysiologie Forestières, BP239, F-54506 Vandoeuvre lès Nancy, France
3 Corresponding author (daniel.epron{at}scbiol.uhp-nancy.fr)
4 INRA, UMR 1092 Laboratoire d’Etude des Ressources Forêt-Bois, F-54280 Champenoux, France
5 AgroParisTech, UMR 1092 Laboratoire d’Etude des Ressources Forêt-Bois, F-54000 Nancy, France
6 INRA, UMR 547 Physiologie Intégrée de l’Arbre Fruitier et Forestier, F-63039 Clermont-Ferrand, France
7 Université Blaise Pascal, UMR 547 Physiologie Intégrée de l’Arbre Fruitier et Forestier, F-63177 Aubière, France
 |
Abstract |
|---|
Enhanced sapling growth in advance regeneration requires gaps in the canopy, but is often delayed after canopy opening, because acclimation of saplings to the new environment is gradual and may last for several years. Canopy opening is expected to result in an increased transpiration because of a larger climatic demand and a higher stomatal conductance linked to the higher rates of photosynthesis. Therefore, we focused on the changes in water relations and the hydraulic properties of beech (Fagus sylvatica L.) saplings during 2 years after canopy opening. We tested the hypothesis that an increase in leaf-specific hydraulic conductance and a decrease in vulnerability to cavitation occur to sustain an enhanced transpiration. Hydraulic conductance of defoliated shoots, vulnerability to cavitation, size and density of xylem vessels as well as stomatal conductance were recorded on saplings growing in shade (S saplings) or in gaps created by opening the canopy (shade-to-light, SL saplings). Hydraulic conductance per unit cross-sectional area (KAS) did not differ in the shoots of S and SL saplings. But a higher ratio stem cross-sectional area/leaf area resulted in a higher leaf-specific hydraulic conductance of the shoots (KAL) of SL saplings. Contrary to expectations, vulnerability to cavitation increased transitorily in stems during the first year after canopy opening and no difference was observed between the two treatments in light-saturated stomatal conductance. During the second year, vulnerability to cavitation was similar in the S and SL saplings and light-saturated stomatal conductance increased in SL saplings. These results demonstrate a release of the hydraulic constraints after canopy opening with an adjustment of the ratio stem cross-sectional area/leaf area. But the larger vulnerability to cavitation during the first year could limit stomatal opening and therefore the ability of beech saplings to use the available light for photosynthesis and could therefore partly explain why the growth increase was delayed to the second growing season after canopy opening.
Keywords: acclimation, biomass allocation, gap, hydraulic conductance, vulnerability to cavitation
Received April 7, 2009; Accepted August 1, 2009