Effects of enhanced ultraviolet radiation and carbon dioxide concentration on the moss Hylocomium splendens

Abstract In a laboratory experiment interaction effects of UV‐B and CO 2 on photosynthesis and growth of the moss Hylocomium splendens were studied. The plants were exposed to two CO 2 levels (350 ppm and 600 ppm) and three UV‐B levels (no UV‐B, ambient UV‐B and that corresponding to 20% ozone depletion) for 5 months. The effects were recorded by measuring the photosynthetic response and growth of the plants. There was a statistically significant change in photosynthetic efficiency and maximum photosynthetic rates due to time and to enhanced CO 2 concentration, whereas there was no effect due to UV‐B. There was a decreased growth due to both UV‐B and CO 2 and an interaction effect on growth (in length). The UV‐B dose corresponding to the ambient level had a larger reducing effect on growth than the highest UV‐B dose. This was a counter‐intuitive result and the following tentative interpretation was made: differences in the measured UV‐A/UV‐B/PAR ratios between the treatments could explain the result provided there was a non‐linear response to UV over the range of irradiance levels used.