Document: FEN-3-32-43

Seasonal water relations of juvenile and adult sagebrush (Artemisia tridentata ) in the Columbia Basin, Washington.

KHAN, F.* and J.L.DOWNS

Pacific Northwest National Laboratory, Richland, WA ¹

Abstract:
Big sagebrush (Artemisia tridentata) is a dominant, native shrub of the Columbia Basin and other semi-arid regions in the western United States where plant growth is limited by water availability. In these regions, small plants with shallow roots often experience low water availability during the summer while larger, well-established plants with deep roots are able to access soil water at depth. We examined water relations in two size classes (non-reproductive juvenile and reproductive adult) of big sagebrush on a monthly basis over a year period. Because juvenile shrubs generally have shallower rooting depths than adult shrubs, we expected juvenile shrubs to experience greater midday water stress than adults during periods of growth and during summer drought. We also hypothesized that juvenile sagebrush plants would incur more negative pre-dawn xylem potentials than adult shrubs that could access moister soil at depth. Pre-dawn and midday xylem potentials were measured each month from November 1998 to October 1999, excluding January 1999. We found significantly lower pre-dawn xylem potentials for adult shrubs in August and September, but no significant differences in pre-dawn xylem potentials were found between size classes in any other months. Significant differences in midday xylem potentials were found between the two size classes for all months of the study period. During late fall and winter months, juveniles exhibited lower midday xylem potentials, whereas adult shrubs exhibited more negative midday xylem potentials in the spring, summer and early fall. Pre-dawn values for both size classes were most negative in October ( 3.2 MPa) before the fall rains and least negative in early April ( 0.7 MPa) after winter recharge. Midday values for adult shrubs were more negative in August and September ( 3.7 MPa and 3.6 MPa respectively) during flowering, and least negative in March ( 1.5 MPa), and for juvenile shrubs, the values were more negative in August ( 3.2 MPa) and least negative in April ( 1.5 MPa).

Keywords: Artemisia tridentata, plant water relations, xylem potentials

This abstract is being presented at: 3:30 PM in session:
WATER RELATIONS