The reduction of aboveground Calamagrostis epigeios mass and tiller number by enhanced UV-B in a dune-grassland ecosystem

Since early May 1997 dune-grassland vegetation in the Netherlands has been exposed to enhanced levels of ultraviolet-B (UV-B) radiation. Expected increases in the amount of biologically effective UV-B (UV-B_BE) upon a reduction of the stratospheric ozone layer with 15% were calculated and artificially supplemented.In June and September 1998, above- and belowground vegetation samples were taken. Of the dominant species Calamagrostis epigeios and Carex arenaria aboveground mass accumulation, leaf weight (LW), leaf area (LA), specific leaf area (SLA) and tiller number were assessed separate from the remaining vegetation.The results of our study indicate alterations in the vegetation structure due to UV-B supplementation. In June, a significant reduction due to UV-B supplementation in number of tillers and aboveground dry weight per soil area unit was found for C. epigeios. As C. epigeios is the most dominant species of the dune-grassland, these effects indicate a change in vegetation structure due to UV-B enhancement. Indications of UV-B effects on other parameters, such as the number of tillers of C. arenaria and aboveground plant dry weight of the group of species other than C. epigeios and C. arenaria, may also represent changes in vegetation structure. The LA and LW data show the same patterns as the mass accumulation trends. No significant UV-B effects on the SLA of the species or of the total vegetation could be found.Trends in patterns of species dry weight accumulation and partitioning of dry weight between species groups are different in June and September. This may indicate seasonal dependence of UV-B responses. Also, the consistently reducing trend in total and aboveground plant dry weight may indicate deleterious effects of UV-B on total plant matter accumulation. Possible causes of observed trends and effects are discussed.