© 2003 Heron Publishing—Victoria, Canada
Patterns of stomatal conductance among blue oak (Quercus douglasii) size classes and populations: implications for seedling establishment
Steven L. Matzner (1, 2), Kevin J. Rice (3) and James H. Richards (4)
1. Department of Biology, Augustana College, Sioux Falls, SD 57197, USA / 2. Author to whom correspondence should be addressed (steven_matzner@augie.edu) / 3. Department of Agronomy and Range Science, University of California, Davis, CA 95616, USA / 4. Department of Land, Air, and Water Resources, University of California, Davis, CA 95616, USA / Received July 25, 2001; accepted February 23, 2003; published online July 1, 2003
Summary
Quercus douglasii Hook. & Arn. (blue oak) is a deciduous white oak that is currently failing to regenerate throughout much of its range in
California, USA. Patterns of water use were observed in adult trees, saplings and seedlings to determine if ontogenetic changes
in water use occur, which might be important in the establishment of this long-lived perennial species in a Mediterranean-type
system. Seasonal and diurnal stomatal conductance (gs), late-season predawn xylem water potentials (Ψpre), carbon isotopic ratio (δ13C) and soil water status were compared among the three size classes at three sites differing in mean precipitation and soil
water characteristics. Comparisons were also made between microsites with and without regeneration (defined by the presence
or absence of saplings).
Overall patterns of water use were consistent among the three sites, except that, at the site with the highest rainfall, Q. douglasii plants had higher gs and more positive Ψpre values. Although no differences in water use patterns were found between regeneration and non-regeneration microsites, the
observed ontogenetic differences in water use may have important implications for Q. douglasii establishment. Compared with adult trees and saplings, seedlings had higher gas exchange rates during periods of high soil
water content (early in the season and in the morning). Seedling gs was correlated with percent extractable soil water (ESW) throughout the season; adult tree and sapling gs was correlated with ESW between June and September. Despite experiencing greater water stress (indicated by more negative
Ψpre values) than older trees, seedlings had more negative δ13C values, implying lower water-use efficiencies.
Keywords:
carbon isotope ratios, extractable soil water, ontogenetic, water potential, water-use efficiency.
