Growth and pigment production in two subarctic grass species under four different UV-B irradiation levels

The aim of the experiment was to test the sensitivity of grasses from a subarctic region to a range of different ultraviolet-B (UV-B, 280-320 nm) levels. Seedlings of Calamagrostis lapponica and tillers of Calamagrostis purpurea were grown for 50 days in a greenhouse at 4 different levels of UV-BB, radiation (no UV-B, ambient W-B,UV-B corresponding to 15 and 25% ozone depletion, respectively, at 68 degrees N, northern Sweden on July 27th). In C. purpurea total plant dry weight was significantly reduced at the 15% level compared to all other treatments, whilst tiller number was reduced when compared to the non UV-B treatment only. Reduced growth at the 15% level was accompanied by significant increases in shoot to root ratio (S:R), leaf area ratio (LAR) and leaf weight ratio (LWR), which were due to changes in both specific leaf area (SLA) and root growth. Similarly, in C. lapponica there were reductions in total dry weight at the 15% level, although differences in partitioning were only observed in LWR which was significantly greater than in the non UV-B treatment. There was a difference in tiller number in C. lapponica between all treatments. A reduced number of tillers was observed with increasing W-B exposure from zero UV-B to the 15% level, whilst tiller number was significantly higher at the 25% level than in all other treatments. In C. lapponica, differences were apparent in the amount of UV absorbing pigments. Plants exposed to ambient UV-B and the 15% level had significantly more UV-B absorbing compounds than those in the 25% and non UV-B treatments. All these results suggest that the 15% ozone depletion level was the most harmful to plant growth and few damaging effects were observed at the higher 25% ozone depletion level.