EFFECTS OF ENHANCED ULTRAVIOLET-RADIATION AND CARBON-DIOXIDE CONCENTRATION ON THE MOSS HYLOCOMIUM SPLENDENS

In a laboratory experiment interaction effects of UV-B and CO2 on phot osynthesis and growth of the moss Hylocomium splendens were studied. T he plants were exposed to two CO2 levels (350 ppm and 600 ppm) and thr ee UV-B levels (no UV-B, ambient UV-B and that corresponding to 20% oz one depletion) for 5 months. The effects were recorded by measuring th e photosynthetic response and growth of the plants. There was a statis tically significant change in photosynthetic efficiency and maximum ph otosynthetic rates due to time and to enhanced CO2 concentration, wher eas there was no effect due to UV-B. There was a decreased growth due to both UV-B and CO2 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-intui tive result and the following tentative interpretation was made: diffe rences in the measured UV-A/UV-B/PAR ratios between the treatments cou ld explain the result provided there was a non-linear response to UV o ver the range of irradiance levels used.