Metabolic Acclimation to Temperature in Arctic and Alpine Ecotypes of <i>Oxyr1A Digyna</i>

Abstract

Interactions on metabolism between ecotype and temperature acclimation were studied in a series of arctic and alpine populations of Oxyria digyna (L.) Hill, a widespread tundra plant species. Net photosynthesis, dark respiration, Hill reaction of isolated chloroplasts, and mitochondrial oxidative activity were measured. The principal question was “What is the relative effect of phenotypic temperature acclimation on metabolic rates as compared to the effect conferred by the ecotype?” Dark respiration rates were increased by cold acclimation in all ecotypes. Maximum net photosynthesis rates were lowered in all arctic populations but in only a few alpine populations after warm acclimation. The temperature of maximum net photosynthesis was increased by warm acclimation. Maximum net photosynthesis rates were higher in arctic populations than in alpine ones; this difference was increased by cold acclimation. The upper temperature compensation point in both arctic and alpine ecotypes was increased by warm acclimation. Alpine populations showed ideal homeostasis in net photosynthesis while arctic ecotypes showed only a low degree of partial homeostatic adjustment in net photosynthesis. Dark respiration homeostasis was almost ideal in all populations and showed no ecotypic difference. Efficiency of chlorophyll was higher in alpine ecotypes and at high temperature in all ecotypes, particularly after warm acclimation. Cold acclimation increased Hill reaction activity by isolated chloroplasts from alpine populations after growth at 14-hr photoperiod, but depressed the rate in arctic populations at 14 hr. At 20-hr photoperiod, the Hill rate was higher after cold acclimation in all populations tested. Mitochondrial oxidative activity was increased by cold acclimation; the rates from arctic populations were higher after cold treatment than those from alpine populations. We conclude that, in Oxyria, acclimation is under genetic control and that “acclimation ecotypes” exist; the most plastic phenotypes in regard to acclimation occur in the alpine ecotypes.