Respiration rates, thermal sensitivity, and thermal acclimation potential of root respiration were investigated in Ranunculus from the Arctic. Comparisons of three species (R. glacialis, R. nivalis and R. acris subsp. pumilus) used plants grown on a mountain or in a glasshouse for 6 wk at contrasting soil temperatures (5.4 and 14.5 degreesC, respectively). Northern and southern ecotypes of two species of Ranunculus (R. pygmaeus, and R. acris subsp. acris), together ranging from Svalbard (79 degreesN) to Scotland (56 degreesN), were similarly compared after 2 wk in a growth cabinet at 5 and 15 degreesC. Respiration rates varied at standard measurement temperatures; R. nivalis and R. pygmaeus grown on the mountain or at 5 degreesC had the highest respiration, followed by other alpine snowbed species (R. glacialis and R. acris subsp. pumilus) and R. acris subsp. acris from the arctic lowland; R. acris subsp. acris from Scotland had lowest rates. Respiration was temperature sensitive for all populations, increasing progressively between 5 and 20 degreesC (Q(10) ((5-15)): 1.2-2.4). Extent and type of acclimation of root respiration varied with no clear latitudinal pattern emerging. Acclimation to a 10 degreesC increase in growth temperature was achieved through: change in temperature sensitivity (shown by changes in Q(10 (5-15)) values) (R. acris subsp. pumilus); or reduction in absolute rates (R. pygmaeus from Svalbard, R. acris subsp. pumilus and R. nivalis). Complete acclimation occurred in R. acris subsp. pumilus and R. pygmaeus, whereas R. acris subsp. acris from Scotland and R. glacialis did not acclimate. Plants that adjust root respiration (e.g., R. pygmaeus from Svalbard and R. acris subsp. pumilus) to maintain a positive carbon balance, may tolerate predicted temperature increases in arctic regions. Plants with high rates of root respiration and/or high sensitivity to temperature as well as poor acclimation potential, (e.g., R. glacialis) may only persist in cold microhabitats.