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-ambi ent UV radiation, UV-B enhanced treatment, and two controls) applied t o 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 bloc k UVR or enhance UV-B irradiance. Sunlamps increased UV-B irradiance a bove ambient levels by an average of 15% during clear skies and 40% un der 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. neomexica na in the shade. However, moss in the enhanced treatment in the open h ad a lower biomass (19.57 mg cm(-2)) than moss growing under ambient c onditions (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 maximu m amount of solar radiation striking the stream bottom from 7 hrs to a n average of 3.5 hrs to 2.5 hrs per day in the open and to approximate ly 45 min to 20 min per day in the shade (sunflecks). Our results sugg est that a 15% to 40% increase in UV-B may have a harmful impact on th is moss.