Persisting soil drought reduces leaf specific conductivity in Scots pine (Pinus sylvestris) and pubescent oak (Quercus pubescens)

Leaf specific conductivity (LSC; the ratio of stem conductivity (KP) to leaf area (AL)), a measure of the hydraulic capacity of the stem to supply leaves with water, varies with soil-water content. Measured wood anatomic variables and tested how LSC of similar-sized trees of the same population, under similar climatic conditions, responds to persistently wet or dry soil.

Scots pine (Pinus sylvestris L.) and pubescent oak (Quercus pubescens Willd.) trees were compared between a dry site and a wet site in the Valais, an inner alpine valley in Switzerland. We found that soil-water content strongly influenced AL and KP and the plant components affecting KP, such as conduit radius, conduit density, and functional sapwood area. Trees at the dry site had lower LSC than trees with the same stem diameter at the wet site. Low LSC in trees at the dry site was associated with a smaller functional sapwood area and narrower conduits, resulting in a stronger reduction in KP than in AL. These observations support the hypothesis that trees maintain a homeostatic water-pressure gradient. An alternative hypothesis is that relatively high investments in leaves compared with sapwood contribute to carbon gain over an entire season by enabling rapid whole-plant photosynthesis during periods of high water availability (e.g., in spring, after rain events and during morning hours when leaf-to-air vapor pressure deficit is small). Dynamic data and a hydraulic plant growth model are needed to test how investments in leaves versus sapwood and roots contribute to transpiration and to maximizing carbon gain throughout entire growth seasons


  • Dr. R. Zweifel, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Switserland


MSc theses

  • Chowdhury, Q. (2006). Effects of water availability on hydraulic architecture of Quercus pubescens Willd. and Pinus sylvestris L. in the Wallis Valley, Switzerland. (supervision: Sterck, Sass-Klaassen, in cooperation with Zweifel/Inst.f.Planzwissenschaften, Bern)
  • Brock, S. de (2006). The pipe model theory tested for pines and oaks dry versus wet forests in the Wallis valley, Switzerland. (supervision: Sterck, Sass-Klaassen, in cooperation with Zweifel/Inst.f.Planzwissenschaften, Bern)
  • Chitiki, A. (2005). Developmental trajectories of pubescent oak (Quercus pubescens) and Scots pine (Pinus sylvestris) in drought-stressed environments in the Wallis Valley, Switzerland (supervision: Sterck, Sass-Klaassen, in cooperation with Zweifel/Univeristy of Bern)