ECCLES, CHRIS* and DARREN R. SANDQUIST. Department of Biological Science, California State University, Fullerton, CA 92834. - Temperature acclimation of photosynthesis in four populations of the desert shrub Encelia farinosa.
Perennial desert plants experience a broad range of temperatures over
the course of their active growing season. Changing the optimal
temperature for photosynthesis (thermal acclimation) is one adaptive
mechanism for tolerating such fluctuations, but not all species are
known to have this capability. Previous studies found that thermal
acclimation is absent in the genus Encelia, although
comparisons among species in this genus indicate that the capacity for
evolutionary change in thermal optimum exists. We investigated
thermal-acclimation potential in four populations of Encelia
farinosa which span a broad temperature gradient. In each
population there was some evidence of thermal acclimation, but the
degree of acclimation was small in comparison to the temperature range
in which the plants were grown. The thermal optimum for all
populations was fairly consistent for plants raised in high
temperature, but thermal optimum for plants raised at lower
temperatures was correlated with average minimum spring temperatures
of the population’s habitat. These results suggest that some local
adaptation for optimal photosynthetic temperature exists in this
species, but that thermal acclimation may be limited as a mechanism
for tolerating large seasonal temperature changes.
Key words: desert, Encelia, photosynthesis, thermal acclimation