Short-term effects of ambient and enhanced UV-B on moss (Fontinalis neomexicana) in a mountain stream

We examined the influence of UV-B radiation on Fontinalis neomexicana by comparing the growth of moss under four light regimes (90% PAR-ambient UV radiation, UV-B enhanced treatment, and two controls) applied to both an open and a shaded section of West Saint Louis Creek (2,850 m a.s.l.). Clear Plexiglas shields and FS 40 sunlamps were used to block UVR or enhance UV-B irradiance. Sunlamps increased UV-B irradiance above ambient levels by an average of 15% during clear skies and 40% under cloudy conditions. This increase was equivalent to 428.7 Einst/m(2)-day in the open and 136.7 Einst/m(2)-day in the shade. After 70 days, enhanced levels of UV-B had no effects on the growth of F. neomexicana in the shade. However, moss in the enhanced treatment in the open had a lower biomass (19.57 mg cm(-2)) than moss growing under ambient conditions (28,47 mg cm(-2)). We were unable to conclusively determine the effects of ambient levels of UV radiation (UVR) on F. neomexicana. It is, however, worth noting that clouds reduced the potential maximum amount of solar radiation striking the stream bottom from 7 hrs to an average of 3.5 hrs to 2.5 hrs per day in the open and to approximately 45 min to 20 min per day in the shade (sunflecks). Our results suggest that a 15% to 40% increase in UV-B may have a harmful impact on this moss.