DIFFERENTIAL-EFFECTS OF ELEVATED ULTRAVIOLET-B RADIATION ON PLANT-SPECIES OF A DUNE GRASSLAND ECOSYSTEM

In a greenhouse study, plants of three monocotyledonous and five dicot yledonous species, which occur in a Dutch dune grassland, were exposed to four levels of ultraviolet-B (UV-B) radiation. UV-B levels simulat ed up to 30% reduction of the stratospheric ozone column during summer time in The Netherlands. Six of the plant species studied in the green house were also exposed to enhanced UV-B irradiance in an experimental field study. In the field experiment plants either received the ambie nt UV-B irradiance (control) or an enhanced UV-B level simulating 15-2 0% ozone depletion during summertime in The Netherlands. The purpose o f both experiments was to determine the response of the plant species to UV-B radiation and to compare results obtained in the greenhouse wi th results of the field experiment. Large intraspecific differences in UV-B sensitivity were observed in the greenhouse study. Total dry mat ter accumulation of monocotyledons was increased, while dry matter acc umulation of dicotyledons remained unaffected or decreased. The increa se in biomass production of monocotyledons at elevated UV-B was not re lated to the rate of photosynthesis but to alterations in leaf orienta tion. In the greenhouse study, UV-B radiation also affected morphologi cal characteristics. Shoot height or maximum leaf length of five out o f eight species was reduced. In the field study only one species showe d a significantly decreased maximum leaf length at enhanced UV-B. Poss ible reasons for this discrepancy are discussed. The absorbance of met hanolic leaf extracts also differed between species. UV absorbance of field-grown plants was higher than greenhouse-grown plants. In the gre enhouse study, the highest UV-B level increased UV-B absorbance of som e species. In the field study however, this stimulation of UV absorban ce was not observed. In general, results obtained in the greenhouse st udy were similar to results obtained in the field study. Difficulties in extrapolating results of UV-B experiments conducted in the greenhou se to the field situation are discussed.