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The effect of solar radiation and monochromatic UV radiation on the motility of the filamentous cyanobacterium Phormidium uncinatum was determined. Solar radiation (mid-day, in midsummer at a location near Lisboa, Portugal) was found to impair motility within about 30 min. This effect is neither a result of a temperature increase nor of visible light. The spectral sensitivity determined using the Okazaki Large Spectrograph shows the maximal effectiveness of radiation of ^300 nm. The short time requirement for the response and the lack of any photoreactivation of motility argues against DNA being the UV target. Investigations using reagents diagnostic of superoxide free radicals and singlet oxygen failed to confirm...
Reduced water depth in dry years has been proposed to interact with ultraviolet-B (UV-B) radiation and a pathogenic fungus to cause episodes of high mortality of amphibian embryos. Observations of breeding phenology of boreal chorus frogs (Pseudacris maculata) in Colorado from 1986 to 2001 show that dry years result in earlier breeding. The earliest and latest dates of maximum calling activity by males were 20 May and 16 June, and the date of maximum calling was strongly related to the amount of snow accumulation during the winter. Surface UV-B flux, estimated from satellite-based measurements, was positively related to date of maximum calling. In dry years, surface UV-B during calling was reduced by an amount similar...
In arid ecosystems, as much as 75% of solar radiation that penetrates the atmosphere hits the surface of the soil. The combination of high irradiance, high temperature, and low moisture puts constraints on the activity and organization of microbial communities. To separate the direct effects of UV absorbance on litter decomposition from the indirect effects of microbial selection, we placed mixed cohorts of senescent pi´┐Żon (Pinus edulis) and juniper (Juniperus monosperma) litter into triplicate microcosms assigned to four treatments: UV irradiated (0.6 mW/cm2 UV-A and UV-B for 12 h/day), with and without water additions, and non-irradiated with and without water additions. After 26 weeks, mass loss rates did not...