In a survey of several plant species found at Churchill, Manitoba, in the transition zone between the low and subarctic regions, we measured leaf respiration in terms of total respiration and alternative pathway respiration rates. Leaves of arctic plants exhibit higher rates of total respiration and alternative (cyanide insensitive) respiration than temperate species. There is a negative correlation between plant height and alternative pathway activity. Shorter plants have higher rates of alternative pathway respiration. More alternative pathway activity may mean that there is less energy in the form of ATP available for growth. A shorter growth habit keeps these plants in the still air close to the ground. This prevents cooling, water loss and physical damage due to wind abrasion. Thus plants with high rates of alternative pathway respiration may be better adapted to the arctic environment. The alternative pathway respiration of Orchis rotundifolia was shown to be under the influence of the biological clock.Key words: Subarctic, plant respiration, alternative pathway, cyanide insensitivMots clés: subarctique, respiration des plantes, voie alterne, insensible au cyanur
