Photoinhibition as a factor in altitudinal or latitudinal limits of species

Evidence is provided that in sunny conditions, exposure to continuous sunli ght in the arctic can lead to down regulation of photosynthesis. This down regulation effectively protects Leaves from photodamage, with no evidence f or significant irreversible photoinhibition being found for any of a number of different dwarf shrub species studied in a high arctic environment. Dow nregulation was less apparent under cloudy conditions. These results are di scussed in relation to possible accumulation of carbohydrate carbohydrate a nd differences in respiratory metabolism.