We studied species-specific growth responses of freshwater algae to solar ultraviolet radiation (UVR) by measuring growth-irradiance curves (G-E curves) of 17 algal diatoms (isolated from a periphyton community in a lotic system) in a solar simulator under photosynthetically available radiation plus UVR and minus UVR radiation condition. Algal growth responses to UVR were highly species-specific, and the photoinhibition parameter (β) of the +UVR condition differed greatly among species. We compared the degree of UVR effect on algal growth (UVR inhibition index: difference in β between +UVR and -UVR conditions) with parameters derived from the G-E curve and with algal cell morphology. UVR inhibition indexes significantly correlated with the initial slope of light-limited portion of G-E curve (α) and with the irradiance at which the growth rate starts to saturate (Ek), but not with the cell surface to volume ratios. Low-light-adapted algae tended to be more susceptible to growth inhibition by UVR than high-light-adapted ones. Algae that formed dense colonies in the growth medium were relatively tolerant of UVR irrespective of Ek values. Although past studies have emphasized that UVR effects on algae are algal-size dependent, the growth strategies dealing with solar radiation and algal growth forms appear to be more valid in correctly interpreting species-specific responses of algae to solar UVR.
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