Bryophytes are important primary producers in mountain streams and they should be protected against the adverse effects of the high levels of UV-B radiation typical of these environments. The accumulation of UV-absorbing compounds could be one of the mechanisms of protection. A survey of methanol-extractable UV-absorbing compounds (MEUVAC) was conducted for 14 aquatic bryophytes, 10 mosses, and four liverworts, from a mountain stream located at 2,000 m elevation. For four species, several populations were investigated. Absorbance spectra between 250 and 400 nm were obtained and the amount of MEUVAC was calculated per unit of both dry mass (DM) and surface area. Levels of MEUVAC and the absorbance spectra of UV radiation were significantly affected by species. The high levels of MEUVAC and the clearly hump-shaped spectra in the UV-B and UV-A wavelengths (280–400 nm) that were found in the liverworts contrasted with the low levels and non hump-shaped spectra generally found in the mosses (except for Polytrichum commune). Sclerophylly and intraspecific variability only had a modest influence on the results. It may be concluded that the accumulation of MEUVAC might represent a protecting mechanism against UV-B radiation in the four liverworts studied, but rarely in the mosses of this stream.
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