Water potential, leaf conductance, growth, nitrogen
content, and seedling survival of Wyoming Big Sagebrush
(Artemisia tridentata ssp. wyomingensis) following
defoliation of the herbaceous understory were assessed
during two growing seasons. Precipitation was 107% and 63%
of the long-term mean (283 mm) in 1989 and 1990,
respectively, which presented an opportunity to study
impacts during a drought and a non-drought year. Response
of Artemisia was measured on a site seeded to Agropyron
desertorum in the late 1960s, and a native site with Stipa
thurberiana, Festuca idahoensis and Poa sandbergii in the
understory. The two sites were analyzed as separate
experiments.
The dry year had a significant effect on plant water
relations and growth of Artemisia on both sites. Pre-dawn
water potentials averaged 1.23 MPa more negative on the
seeded site and 1.22 MPa more negative on the native site in
1990 compared to the previous year. Mid-day water potential
averaged 1.22 MPa more negative on the seeded site and 1.13
MPa more negative on the native site in 1990 compared to
1989. Morning leaf conductance in 1990 was 61% lower on the
seeded site and 51% lower on the native site than in 1989.
Mean afternoon leaf conductance in the drought year was 62%
less on the seeded site and 63% less on the native site.
Nitrogen content in current year's growth was reduced 29% on
the seeded site and 18% on the native site from 1989 to
1990. Vegetative and reproductive shoot (stem plus leaves)
weights were reduced by over 80% in 1990 compared to 1989.
Other production variables showed similar reductions in the
drought year.
Nitrogen content was 11% greater in current year's
growth from shrubs on control as opposed to defoliated plots
on the native site in 1989. Shrubs on control plots had 8%
heavier reproductive stems per unit of canopy, and 7% longer
vegetative stems than shrubs on defoliated plots in 1989 on
the seeded site. Shrubs on control plots had 18% fewer
annual leaves per unit of vegetative shoot, but 12% more
primary ephemeral leaves per vegetative shoot than shrubs on
defoliated plots in 1990 on the seeded site. In 1990,
shrubs on control plots on the seeded site had 11% more
ephemeral leaves per vegetative shoot while shrubs on the
control plots on the native site had 8% fewer ephemeral
leaves per vegetative shoot.
Large shrubs generally had more and heavier leaves, and
longer and heavier stems than medium shrubs. Exceptions
included large shrub lateral stems were 30% shorter than
those of medium shrubs, and large shrubs had 37% fewer
annual leaves per vegetative shoot than medium shrubs in
1989 on the seeded site.
Drought had substantial negative impact on water
relations and growth of Wyoming big sagebrush, while
defoliation of understory vegetation had little effect. / Graduation date: 1993
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/36059 |
| Date | 29 January 1992 |
| Creators | Purrington, Teal Mackenzie |
| Contributors | Miller, Richard F., Doescher, Paul S. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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