Two aspects of drought resistance were investigated on wet and dry ecotypes
of three conifer species: 1) the relative importance of drought avoidance and
drought tolerance mechanisms in resisting drought stress was assessed on Douglas-fir
(Pseudotsuga menzieseii) and lodgepole pine (Pinus contorta) seedlings, and 2)
the effects of drought on root hydraulic conductance and low temperature, on root
water flow rates Were assessed on first-year seedlings of Douglas-fir, lodgepole
pine and white spruce (Picea glauca).
To study drought avoidance, Douglas-fir and lodgepole pine seedlings were
grown in sealed containers in wet (522% water content) or dry (318% water
content) peat/vermiculite soil in a factorial treatment design. Dry weights, water
use, and root length were determined for seedlings at each of five harvests and
stomatal conductance and shoot water potentials were measured during the last 12
weeks of the experiment. Lodgepole pine seedlings had greater dry matter
production, water use, stomatal conductance and new root length than Douglas-fir
seedlings. New root weight of lodgepole pine seedlings exceeded that of Douglas-fir
seedlings during the last five weeks of the experiment, and specific root length
of new roots was higher for lodgepole pine seedlings throughout the experiment.
Douglas-fir seedlings showed higher water use efficiency (WUE) than lodgepole
pine seedlings, although water uptake rates per unit of root dry weight showed
little difference between species. Soil water treatment influenced specific root
length of new roots, water uptake per unit of new root length, and WUE in
Douglas-fir seedlings more than in lodgepole pine seedlings.
To study drought tolerance, Douglas-fir and lodgepole pine seedlings were
grown under drought and well-watered conditions. At each of three harvests a
pressure-volume curve was produced for each seedling. Douglas-fir maintained a
lower osmotic potential at full saturation [special characters omitted] and lower turgor loss point [special characters omitted] than lodgepole pine under both watering regimes,. Both species had lower
[special characters omitted] when drought-stressed.
Douglas-fir appears to be a more conservative species, maintaining low
stomatal conductance and tolerating drought conditions, whereas lodgepole pine
avoids drought by producing large amounts of roots to exploit the soil resource.
To study root hydraulic conductance (Lproot) and water flow rates through
roots (WFRR), water flow was measured through de-topped roots of Douglas-fir,
lodgepole pine, and white spruce seedlings in a pressure chamber. In a drought
experiment, seedlings were grown in sandy soil in a greenhouse under drought and
well-watered conditions during their first growing season and, in a low temperature
experiment, seedlings were grown in sandy soil in growth chambers at 25/20°C
(day/night) and 15/10°C,
In the drought experiment, water flow through roots was measured at three
pressures. No differences in Lproot were found for Douglas-fir and white spruce
seedlings grown under the two watering regimes, however, lodgepole pine
seedlings had reduced Lproot when grown under drought conditions. Welk
watered seedlings of lodgepole pine and white spruce had higher Lpr00t in 1989
than in 1990 whereas Douglas-fir seedlings had the same Lproot in both years.
In the low temperature experiment, WFRR was measured at 1.0 MPa and
temperatures of 20°C for 24 hours or 20°, 12°, and 4°C for 18, 15, and 15 hours
respectively. At 20°C, white spruce seedlings had higher WFRR than the other
two species. Lodgepole pine and white spruce seedlings grown in the 1S°/10°C
growth chamber had higher WFRR than seedlings grown in the 25°/20°C growth
chamber. Water flow rate decreased with temperature in all three species. After
correcting for viscosity, all seedlings had lower WFRR with reduced temperature,
except for Douglas-fir and white spruce seedlings grown at 15°/10°C which had
the same WFRR at 20°C and 12°C. Therefore, Douglas-fir and white spruce
seedlings were found to become less sensitive to low temperature (chilling) stress
when pre-conditioned at low temperatures.
In the drought and low temperature studies, dry weight biomass of white
spruce was lowest but white spruce had a greater specific root length than
lodgepole pine and Douglas-fir. In the drought study, biomass production in
seedlings from wet ecotypes of each species was more reduced when drought-stressed than seedlings from dry ecotypes. / Graduate
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/9656 |
| Date | 10 July 2018 |
| Creators | Smit, Julie |
| Contributors | van den Driessche, R., Owens, John N. |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | Available to the World Wide Web |
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