AbstractIn a laboratory experiment interaction effects of UV‐B and CO2on photosynthesis and growth of the mossHylocomium splendenswere studied. The plants were exposed to two CO2levels (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 CO2concentration, whereas there was no effect due to UV‐B. There was a decreased growth due to both UV‐B and CO2and 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
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