Ultraviolet radiation impact on lichen growth

Abstract

This study investigates relative growth rates and brown pigments synthesis under the influence of UV-B radiation in short term growth chamber experiments. One chlorolichen, Cetraria islandica, and the two cephalolichens Lobaria pulmonaria and Peltigera aphthosa were cultivated for two-weeks at two treatments, PAR and PAR+UV-B. PAR level was 125 μmol photons m-2 s-1 for 12h photoperiod and UV-B level was 1 Wm-2 for 6 h in the middle of the photoperiod. All three lichen species responded significantly to applied treatments. General Linear Model was performed with growth parameters (RGR, RTAGR) as responses and treatment as factor. UV-B had adverse impact on lichens by decreasing both the RGR and RTAGR. By contrast, PAR treatment (no UV-B) supported high RGR and RTAGR for all three lichens. However, P. aphthosa was more affected by UV-B radiation than C. islandica and L. pulmonaria. Peltigera aphthosa had negative RGR and RTAGR due to photoinhibition. Chl a and b were measured in two solutions, in DMSO and in ethanol. There were no significant differences in Chl a+b, Chl a/b and brown pigments synthesis between treatments.

A second growth chamber experiment was run with only L. pulmonaria for 3-weeks at two treatments, PAR+UV-B+UV-A and PAR+UVA, to investigate the role of high intensity UVA and PAR in brown pigments synthesis. In the PAR+UV-B+UV-A treatment, the level of UV-A and UV-B were 7 and 0.4 Wm-2, respectively, and PAR was 500 μmol photons m-2 s-1. In the PAR+UV-A treatment, polyester had been placed to screen UV-B, the level of UV-A beneath the polyester was 5.6 Wm-2 and the PAR level was same. Photoperiod was 12 h; UV radiation for 8 h in the middle of the daily 12h photoperiod for both treatments. Chl a+b and brown pigment synthesis significantly differed between the treatments. Brown pigment synthesis was twice as high at PAR+UV-B+UV-A than at PAR+UVA. The higher brown pigments synthesis in this second experiment suggests that higher intensity of UV-A and/or PAR boost the synthesis of brown pigments in the lichens.