ISSN:
0931-1890
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Notes:
Abstract We investigated whole tree water relations in 56–65 m tall, old-growth Pseudotsuga menziesii trees within the Wind River Canopy Crane site, Carson, Washington, USA. We measured at predawn and solar noon the vertical gradients in xylem pressure potential using a pressure chamber. On an Abies amabilis sapling located in the understory at the base of one of the study trees, predawn and solar noon xylem pressure potentials were also measured. Xylem pressure potential data were measured from late June through early September 1996 on foliage sampled from 1 to 64.5 m. Over this height gradient, predawn water potentials ranged from –0.23 to –1.10 MPa. Solar noon values showed an even greater range (from –0.44 to –2.51 MPa). At predawn, the water potential gradient approached the theoretical hydrostatic gradient (–0.0105 vs –0.010 MPa m–1). The gradient at solar noon was steeper (–0.0331 MPa m–1). Instantaneous stomatal conductances were not greatly different between young, sapling-sized and old-growth trees [0.094±0.033 (SD) vs 0.086±0.045 cm s–1, respectively]. Stomata of both size classes of trees appeared very sensitive to increasing vapor pressure deficits. A comparison of stable carbon isotope values from the old-growth and sapling-sized trees indicated lower stomatal conductances in the old-growth. This study provides sound documentation regarding the utility of the cohesion theory in the interpretation of water potential gradients. This study also emphasizes inherent differences between sapling-sized and tall, old-growth trees.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s004680050235
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