Differences in leaf gas exchange and water relations among species and tree sizes in an Arizona pine-oak forest

T. E. Kolb, J. E. Stone

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123 Scopus citations


We compared leaf gas exchange and water potential among the dominant tree species and major size classes of trees in an upland, pine-oak forest in northern Arizona. The study included old-growth Gambel oak (Quercus gambelii Nutt.), and sapling, pole, and old-growth ponderosa pines (Pinus ponderosa var. scopulorum Dougl. ex Laws.). Old-growth oak had higher predawn leaf water potential (Ψ(leaf)) than old-growth pine, indicating greater avoidance of soil water stress by oak. Old-growth oak had higher stomatal conductance (G(w)), net photosynthetic rate (P(n)), and leaf nitrogen concentration, and lower daytime Ψ(leaf) than old-growth pine. Stomatal closure started at a daytime Ψ(leaf) of about -1.9 MPa for pine, whereas old-growth oak showed no obvious reduction in G(w) at Ψ(leaf) values greater than -2.5 MPa. In ponderosa pine, P(n) and G(w) were highly sensitive to seasonal and diurnal variations in vapor pressure deficit (VPD), with similar sensitivity for sapling, pole, and old-growth trees. In contrast, P(n) and G(w) were less sensitive to VPD in Gambel oak than in ponderosa pine, suggesting greater tolerance of oak to atmospheric water stress. Compared with sapling pine, old-growth pine had lower morning and afternoon P(n) and G(w), predawn Ψ(leaf), daytime Ψ(leaf), and soil-to-leaf hydraulic conductance (K1), and higher foliar nitrogen concentration. Pole pine values were intermediate between sapling and old-growth pine values for morning G(w) and daytime Ψ(leaf), similar to sapling pine for predawn Ψ(leaf), and similar to old-growth pine for morning and afternoon P(n), afternoon G(w), K1, and foliar nitrogen concentration. For the pines, low predawn Ψ(leaf), daytime Ψ(leaf), and K1 were associated with low P(n) and G(w). Our data suggest that hydraulic limitations are important in reducing P(n) in old-growth ponderosa pine in northern Arizona, and indicate greater avoidance of soil water stress and greater tolerance of atmospheric water stress by old-growth Gambel oak than by old-growth ponderosa pine.

Original languageEnglish (US)
Pages (from-to)1-12
Number of pages12
JournalTree Physiology
Issue number1
StatePublished - Jan 2000


  • Gambel oak
  • Hydraulic conductance
  • Nitrogen
  • Photosynthesis
  • Pinus ponderosa
  • Ponderosa pine
  • Productivity
  • Quercus gambelii
  • Stomatal conductance
  • Vapor pressure deficit
  • Water stress

ASJC Scopus subject areas

  • Physiology
  • Plant Science


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