© 2003 Heron Publishing—Victoria, Canada
Xylem vulnerability to cavitation in Pseudotsuga menziesii and Pinus ponderosa from contrasting habitats
Deborah L. Stout (1, 2) and Anna Sala (1, 3)
1. Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA / 2. Department of Land, Air, and Water Resources, University of California, Davis, CA 95616, USA / 3. Author to whom correspondence should be addressed (sala@selway.umt.edu) / Received February 20, 2002; accepted June 25, 2002; published online December 2, 2002
Summary
In the Rocky Mountains, ponderosa pine (Pinus ponderosa (ssp.) ponderosa Dougl. ex P. Laws. & C. Laws) often co-occurs with Douglas-fir (Pseudotsuga menziesii var. glauca (Mayr) Franco). Despite previous reports showing higher shoot vulnerability to water-stress-induced cavitation in ponderosa
pine, this species extends into drier habitats than Douglas-fir. We examined: (1) whether roots and shoots of ponderosa pine
in riparian and slope habitats are more vulnerable to water-stress-induced cavitation than those of Douglas-fir; (2) whether
species-specific differences in vulnerability translate into differences in specific conductivity in the field; and (3) whether
the ability of ponderosa pine to extend into drier sites is a result of (a) greater plasticity in hydraulic properties or
(b) functional or structural adjustments. Roots and shoots of ponderosa pine were significantly more vulnerable to water-stress-induced
cavitation (overall mean cavitation pressure, Ψ50% ± SE = –3.11 ± 0.32 MPa for shoots and –0.99 ± 0.16 MPa for roots) than those of Douglas-fir (Ψ50% ± SE = –4.83 ± 0.40 MPa for shoots and –2.12 ± 0.35 MPa for roots). However, shoot specific conductivity did not differ between
species in the field. For both species, roots were more vulnerable to cavitation than shoots. Overall, changes in vulnerability
from riparian to slope habitats were small for both species. Greater declines in stomatal conductance as the summer proceeded,
combined with higher allocation to sapwood and greater sapwood water storage, appeared to contribute to the ability of ponderosa
pine to thrive in dry habitats despite relatively high vulnerability to water-stress-induced cavitation.
Keywords:
Douglas-fir, drought tolerance, hydraulic conductivity, leaf-to-sapwood ratio, ponderosa pine, sapwood water storage.
