Growth responses to ultraviolet-B radiation of two Carex species dominating an Argentinian fen ecosystem

Solar ultraviolet-B radiation (UV-B, 280–315 nm) in the Southern Hemisphere has been increasing over the last few decades due to seasonal stratospheric ozone depletion associated with the ‘ozone hole’ and a more general erosion of the stratospheric ozone layer. We studied the effect of UV-B radiation on growth responses of Carex curta and C. decidua, the two most dominant sedges in a fen ecosystem in Tierra del Fuego (Argentina) in field plots and growth chambers where UV-B radiation was manipulated using different transparent plastic films that either transmitted or attenuated UV-B radiation. In the field, leaf and spike elongation of both species was unaffected by UV-B treatments in all four seasons studied (1997/98 through 2000/2001). Specific leaf areas (SLA) were only measured in the last two seasons and remained unaffected by UV-B for both species in the third field season. However, SLA decreased for C. curta in the fourth season but increased for C. decidua under near-ambient UV-B. Ecosystem specific root length was unaffected by UV-B. Although UV-B did not have a statistically significant effect on biomass production, there was a trend for a 15% higher production under near-ambient UV-B in the fourth year (P = 0.064). In the growth chambers, simulated ambient UV-B approximately equivalent to ambient UV-B in Tierra del Fuego stimulated seedling emergence of C. curta but reduced emergence of C. decidua; leaf elongation remained unaffected in both species. While plant morphology of C. curta remained unaffected by UV-B radiation, C. decidua had fewer tillers per plant, however tillers had more leaves and biomass under simulated ambient UV-B than under reduced UV-B radiation. The SLA of C. curta was unaffected by UV-B treatments; however, it was significantly lower for C. decidua under simulated ambient UV-B. Root morphology remained unaffected by UV-B for C. curta but roots of C. decidua were significantly thicker under simulated ambient UV-B. Taken collectively, our findings demonstrate that even moderate changes in UV-B radiation (e.g., corresponding to those expected with current stratospheric ozone depletion) may influence growth, morphology and biomass allocation in a species-specific manner for these native sedges in growth chambers and might also affect competitive relationships of these species in the field. Die ultraviolett-B-Strahlung (UV-B, 280–315 nm) über der Südhemisphäre ist in den letzten Dekaden bedingt durch eine saisonale Abnahme an