Effects of UVB radiation exposure from the molecular to the organism level in macrophytes from shallow Mediterranean habitats

• UV-B radiation affected 4 charophytes and Myriophyllum spicatum in a species-specific way.
• Effects differed at the molecular (DNA damage) to organism (growth) level.
• Charophytes produced more cell-wall bound UV absorbing compounds than vacuolar ones.

The available data on the effects of UVB radiation (UVBR) are scarce for submerged macrophytes, particularly charophytes. We studied the effects of UVBR on Chara baltica, Chara hispida, Chara vulgaris, Nitella hyalina and Myriophyllum spicatum, collected from shallow Mediterranean waterbodies. In a short-term laboratory experiment, we subjected these species to three different UVBR treatments corresponding to daily biologically effective integrated doses of 0, 1 and 6 kJ m−2. The analysed response variables were DNA damage, UV-absorbing compounds (both the methanol-soluble–SUVACs- and, for the first time in charophytes, the methanol-insoluble cell wall-bound fraction–WUVACs-), the stoichiometric composition, photosynthetic pigments, metabolic and growth rates and morphological architecture. UVBR induced harmful effects on DNA in all species, but M. spicatum appeared to be the most sensitive. The observed DNA damage only appeared to be UVB-dose dependent for C. vulgaris. The charophytes produced higher WUVACs levels and the angiosperm higher SUVACs levels. Higher chlorophyll and carotenoid concentrations were detected in the presence of UVBR, but their ratio was not modified by the applied treatments. The Chl a/b ratio decreased under UVBR in two charophyte species, whereas it increased in the angiosperm, which also exhibited a greater photosynthetic response. Relative growth rates were negatively influenced by UVBR, although the degree of this influence depending on the dose was different among species. UVBR modified growth patterns, particularly in those species exhibiting apical growth. We observed more species-specific differences than commonalities in the effects of and responses to UVBR across the investigated species.