Photosynthetic and Respiratory Acclimation to Temperature in Ledum groenlandicum Populations

Abstract

Temperature-related photosynthetic and respiratory acclimation responses were examined in alpine, subarctic, and bog populations of Ledum groenlandicum Oeder, a widespread ericaceous shrub species. Acclimation responses to temperature were measured both after 12- to 16-week exposures to either cool (15? C light - 10?C dark) or warm (30?C light - 25?C dark) thermal regimes and again after each of a series of 2-week exposures to new thermal regimes. Dark respiratory rates were decreased by warm acclimation and increased by cool acclimation. These shifts in rates were frequently completed within 2 weeks in a new thermal regime. Maximal net photosynthetic rates generally did not differ significantly among either populations or thermal regimes; however, the temperature for maximal net photosynthesis in each population was increased to 25?C by warm acclimation and decreased to 20?C by cool acclimation. Net photosynthetic rates were increased at cool temperatures by cool acclimation and increased at warm temperatures by warm acclimation. In contrast to respiratory responses, these photosynthetic acclimation shifts were not completed within 2 weeks in a new thermal regime. Ledum groenlandicum populations differed markedly in their potentials for net photosynthetic and dark respiratory acclimation. Alpine and subarctic populations acclimated to greater degrees than their continental and maritime bog counterparts.