Artemisia tridentataNutt. or big sagebrush is one of the most widespread and economically im-
portant shrubs in western North America. Subspecies vaseyanagrows at slightly higher, cooler, and
drier sites than does A. t.sp.tridentata. Natural hybrids between the two subspecies are commonly
found, for example, on a single hillside, where the parent populations are separated by 85 m in eleva-
tion and 1.1 km along the transect. In 1993, three gardens were established with seedlings from five
populations along the transect planted in each garden [34]. Measurement of water potential and dark
respiration by gas exchange did show differences [35]. Tissue was collected from plants in each gar-
den at several different times of the year and analyzed using calorimetry, which proved to be more in-
structive. The results are shown in Table 3. All populations seem best adapted to their native environ-
ment and most stressed in environments different from their origin. Acclimation, showing phenotypic
plasticity, occurred with change of season. Thus, metabolic distinctions can be made among closely re-
lated populations of plants grown on a single hillside in environments with only slight differences.
Eurotia lanata(Pursh) Moq. (Winterfat) is a small boreal cold-desert shrub that thrives in dry cli-
mates. Seeds were collected in populations from three different elevations and germinated. Metabolic
rates were determined using calorimetry at temperatures from 10 to 20°C. Optimum temperature for
germination, metabolism, and early seedling growth is about 10°C. Stress was noted near 20 and 5°C
(Figure 2). Acclimation during germination had no effect, Differences between the three populations cor-
related with altitude rather than latitude.
B. Drought
Metabolic response to temperature may also be measured during or following treatment with another en-
vironmental stress such as drought. The relative degree of drought tolerance was studied for six popula-
tions of small burnet (Sanguisorba minorScop.) and six cultivars of alfalfa (Medicago sativaL.) grown
TIME, PLANT GROWTH, RESPIRATION, TEMPERATURE 7
TABLE 3 Summary of Data Collected on Different Dates in 1998 on Plant Tissue from Gardens in Salt
Creek Canyon (near Nephi, Utah) of Basin Big Sagebrush (Artemisia tridentataNutt. ssp. tridentata),
Mountain Big Sagebrush (A. tridentatassp.vaseyana), and Hybrids Between Thema
Temperature response (°C)Garden-seed source (date) Low stress Optimal High stress
Basin-basin (Feb. 23, 1998) 10 15 30
Basin-basin (April 22, 1998) 5 15–20 30
Basin-basin (July 21, 1998) 10 30–40 40
Basin-hybrid (Feb. 23, 1998) 10 15 20
Basin-hybrid (April 22, 1998) 5 20–25 30
Basin-hybrid (July 21, 1998) 530 35
Basin-mountain (Feb. 23, 1998) 5 15–25 30
Basin-mountain (April 22, 1998) 5 25–30 35
Basin-mountain (July 21, 1998) 10 20–35 35
Hybrid-basin (Feb. 23, 1998) 5 15–25 30
Hybrid-basin (July 21, 1998) 10 15 30
Hybrid-hybrid (Feb. 23, 1998) 5 10, 25 30
Hybrid-hybrid (July 21, 1998) 10 15–25 35
Hybrid-mountain (Feb. 23, 1998) 5 10, 25 35
Hybrid-mountain (July 21, 1998) 5 10, 20 25
Mountain-basin (April 22, 1998) 5 5–25 30
Mountain-basin (July 21, 1998) 10 10, 15 20
Mountain-hybrid (March 11, 1998) 5 10, 25 30
Mountain-hybrid (April 22, 1998) 15 20, 25 30
Mountain-hybrid (July 21, 1998) 5 10, 30 40
Mountain-mountain (March 11, 1998) 5 10, 25 30
Mountain-mountain (April 22, 1998) 15 25–35 40
Mountain-mountain (July 21, 1998) 5 10, 25 35
aCalorimetric measurements were made every 5 degrees from 5 to 45°C.