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Acclimation of a pleurocarpous moss Pleurozium schreberi (Britt.) Mitt. to enhanced ultraviolet radiation in situ

Authors


Niina M. Lappalainen, fax +358 8 5531061, e-mail: Niina.Lappalainen@oulu.fi

Abstract

We investigated the responses of ultraviolet (UV)-absorbing compounds, chlorophylls a and b, carotenoids and the growth responses of the pleurocarpous moss Pleurozium schreberi (Britt.) Mitt. to enhanced UV radiation in situ. The moss was exposed to a 52% elevation above the ambient level of erythemally weighted UV-B radiation, simulating an approximate 20% reduction in the ozone column, in a dry pine forest in Sodankylä, Finland (67 °22′N, 26 °38′E), under arrays of lamps filtered with cellulose diacetate, which transmitted both UV-B and UV-A radiation. The moss was also exposed to elevated UV-A radiation under control arrays of lamps filtered with Melinex polyester and to ambient radiation under arrays with no lamps in them. Effects of enhanced UV radiation on P. schreberi were recorded during the first 3 years of exposure. Enhanced UV-B radiation did not affect the segment height growth of the moss. The annual dry mass after the second growing season was higher in the UV-A control than in the other treatments, and dry mass decreased significantly during the third treatment year in both UV treatments compared with the ambient. The specific leaf area of the UV-B-treated mosses was significantly higher than the ambient control mosses during the first 2 years. An increase of UV-absorbing compounds was found in the mosses under enhanced UV-B radiation compared with the UV-A control mosses during the first year. Even though the treatment effect on UV-absorbing compounds was transient, the concentrations of these compounds correlated with the amount of UV-A and UV-B radiation received under the elevated UV-B treatment. A correlation with the irradiation of previous days and preceding month of the sampling day was found. A seasonal reduction occurred in the amount of UV-absorbing compounds from the beginning of the summer to late summer. The amount of photosynthetic pigments correlated with the amount of photosynthetically active radiation. The moss P. schreberi was thus found to tolerate increasing UV-B radiation. Our data indicate that P. schreberi tolerates a 52% increase in erythemally weighted UV-B radiation above ambient, responding during the first few years of exposure by increasing UV-absorbing compounds and specific leaf area, and decreasing annual dry mass, and then acclimating to its altered radiation environment.

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