SMITH, BRUCE N. Department of Botany and Range Science, Brigham Young University, Provo, Utah 84602. - Differences in temperature dependence of respiration among subspecies and hybrid populations of big sagebrush: nature vs. nurture.
Artemisia tridentata Nutt. ssp. vaseyana (mountain big sagebrush)
grows at slightly higher, cooler, and drier sites than does A.t. ssp.
tridentata (basin big sagebrush). Natural hybrids between the two
subspecies are found on a single east-facing hillside in Salt Creek
Canyon near Nephi, Utah, where the parent populations are separated by
85 m in elevation and 1.1 km linear distance along the transect. In
1993, three gardens were established with seedlings from five
populations along the transect planted in each garden. Stem water
potential was measured at the site using a Scholander Pressure Bomb.
Gas exchange respiration was measured with an infra-red gas analyzer.
Plant stress was assessed with a chlorophyll fluorescence meter and
carbon isotope ratios. Mineral concentrations in soil and plant tissue
were measured using Inductively Coupled Plasma spectroscopy and
spectrophotometric methods. Calorimetry was used to measure rates of
metabolic heat loss and respiration on the same tissue. Significant
differences were observed among the gardens whatever the source of
origin and among the plant sources in whichever garden they were
grown. Acclimation, showing phenotypic plasticity, occurred with
change of season. Both nature and nurture have an influence. Sagebrush
plants from all sources grow well at cool temperatures (when moisture
is abundant), but are stressed and growth ceases at temperatures much
above 30 C (when moisture is scarce). Sagebrush can become dormant to
withstand high summer temperatures, but may have no mechanism for
slowing growth during very cold conditions, and thus may be damaged if
unprotected (Nelson and Tiernan 1983). Metabolic distinctions are made
among closely related populations of plants grown on a single hillside
in environments with only slight differences, showing physiological
adaptation to very small environmental differences.
Key words: Artemisia tridentata, hybrids, respiration, subspecies, temperature