Reduction in branch sapwood hydraulic permeability as a factor limiting survival of lower branches of lodgepole pine

Abstract

Branch sapwood hydraulic permeability, tracheid size, and earlywood to latewood ratio of annual rings were examined in lower and upper branches of closed-canopy and open-grown lodgepole pine (Pinus contorta Dougl. ex Loud.) trees. Hydraulic permeability, expressed on either a leaf area or sapwood area basis, was lower in lower branches (0.16 × 10 -5 and 5.82 × 10 -5 m 2 , respectively) than upper branches (0.26 × 10 -5 and 10.47 × 10 -5 m 2 , respectively) and was related to narrower tracheids in the sapwood of lower branches. Earlywood/latewood ratio declined in the lower branches of shaded trees. The hydraulic conductivity of upper and lower branches in closed canopy trees was reduced by drilling small holes radially through the stem. Stomatal conductance was lower, and after a growing season there was greater foliage mortality in drilled lower crown branches than in similarly treated upper branches, suggesting that the hydraulic conductivity of lower branches was closer to the lower limit required to maintain foliage than in upper branches. These data suggest that high foliage mortality and eventual death of lower branches does not occur solely because of low light but also from reduced stomatal conductance and photosynthesis resulting from shade-initiated reductions in earlywood, tracheid diameter, and branch hydraulic conductivity.Résumé : La perméabilité hydraulique du bois d'aubier dans les branches, la dimension des trachéïdes et le rapport du bois de printemps sur le bois d'été dans les cernes annuels ont été examinés dans les branches du bas et du haut de pins lodgepole (Pinus contorta Dougl. ex Loud.) croissant à découvert ou dans un couvert fermé. La perméabilité hydraulique, exprimée sur la base de la surface foliaire ou de la superficie d'aubier, était plus faible dans les branches du bas (respectivement 0,16 × 10 -5 et 5,82 × 10 -5 m 2 ) que dans les branches du haut (respectivement 0,26 × 10 -5 et 10,47 × 10 -5 m 2 ) et était reliée aux trachéïdes plus étroites dans le bois d'aubier des branches du bas. Le ratio bois de printemps / bois d'été diminuait dans les branches basses des arbres ombragés. La conductivité hydraulique des branches du bas et du haut des arbres dans le couvert fermé était réduite par de petits trous percés dans le sens radial à travers le tronc. La conductance stomatale était plus faible et il y avait une plus forte mortalité du feuillage après une saison de croissance dans les branches percées de la partie inférieure de la cime que dans les branches du haut traitées de la même façon, ce qui suggère que la conductivité hydraulique des branches du bas est plus près de la limite requise pour maintenir le feuillage que les branches du haut. Ces données suggèrent que la mortalité élevée du feuillage et la mort éventuelle des branches du bas ne surviennent pas seulement à cause de la faible luminosité, mais aussi à cause de la diminution de la conductance stomatale et de la photosynthèse qui résulte de la réduction du bois de printemps, du diamètre des trachéïdes et de la conducti...

Within-crown variation in leaf conductance of Norway spruce: effects of irradiance, vapour pressure deficit, leaf water status and plant hydraulic constraints

“…ex Loud. published by Protz et al [32] seems to support our hypothesis. Of course, further experimental studies on the co-ordination of liquid and gaseous phase conductances in large forest trees should be encouraged at different scales to verify the hypothesis.…”

“…However, there may be a remarkable systematic variation in xylem hydraulic capacity between the branches [15,17,32], and trees growing under low-light conditions produce sapwood with poor water conducting capacity [39,45]. Recently, both the specific and leaf-specific hydraulic conductivity (LSC) have been found to increase with branch insertion height [5,17,32], while in Eucalyptus grandis LSC declined as the branch grew larger [5]. Higher specific conductivity in the upper branches was a result of larger vessel diameter and higher vessel density.…”

Modelling number, vertical distribution, and size of live branches on coniferous tree species in British Columbia

“…Branches on lodgepole pine shoots tended to aggregate into fewer clusters per metre and more branches per cluster (Table 3) than on the other conifer species; hence, the vertical distribution of clusters along young shoots (≤5 years) appeared to be more consistent with the GP model than with the NHPP model. In older shoots (>5 years), there was an apparent convergence to the NHPP model, presumably the effect of branch loss due to mortality associated with carbon limitation in low light levels and reduced branch hydraulic conductivity (Protz et al 2000) as well as random loss to damage and disease. To incorporate predictable patterns of loss will require further testing and development of the GP model.…”

“…Large branches have a greater probability of remaining alive than small ones in the same whorl (Mäkinen and Colin 1999;Hein et al 2007Hein et al , 2008. Self-shading is considered the most likely cause, although reduction in tracheid diameter and hydraulic conductivity is also implicated (Protz et al 2000).…”

Diameter and death of whorl and interwhorl branches in Atlas cedar (Cedrus atlantica Manetti): a model accounting for acrotony

“…Mortality of thin interwhorl branches is due to within-crown competition which results in self-shading among branches in the same tree crown where the light penetration is reduced even in the crown of open-grown trees. Protz et al (2000) considered branch mortality to be mainly driven by light limitations and to be the result of (1) lack of light energy to maintain a positive carbon balance within the branch and (2) the reduction of hydraulic permeability which is also the result of shading. Our results show that the status of a branch is related mainly to size and vertical position, consistent with the acknowledged role of the light in branch survival.…”