AbstractThree species ofSphagnum (S. magellanicum, S. flexuosumandS. rubellum) were exposed to an artificial ozone regime in open-top chambers. Exposure levels consisted of a modified twice ambient (2X) treatment and a charcoal-filtered treatment. Additionally, an open plot treatment was established. The total ozone exposures during the experimental period were 80, 40 and 0.4 ppm in the 2X, open plot and charcoal-filtered treatments, respectively. Ozone level, temperature, humidity, light intensity and NOxlevel were constantly monitored during the experimental period. After ten weeks of exposure the growth (length and dry weight), photosynthesis and chlorophyll content were measured. The study showed that ozone exposure had a significant influence on growth in length, photosynthesis and chlorophyll content. There were also significantdifferences in reaction to ozone among species. Differences in light intensity, humidity, temperature and ozone level between open plots and charcoal-filtered chambers revealed differences in growth in length, biomass, photosynthesis and chlorophyll content between plants in open plots and plants in charcoal-filtered chambers.