Bisexual populations of the charophyte Chara canescens (Desv. et Loisel. in Loisel., 1810) containing male and female individuals are rarely found. Two experiments were carried out to study whether male and female algae from the same site exhibit different physiological capacities, especially with respect to light acclimation. Algae from two different shore levels and from laboratory cultures acclimated to six irradiance conditions (35–500 µmol photons m-2 s-1) were compared. Field measurements showed that both female and male algae of C. canescens are able to acclimate to daily changes in solar irradiance. The quantum yield of Photosystem II (PSII) decreased with increasing irradiance in the morning and increased with decreasing irradiance in the afternoon. Growth experiments showed increasing growth rates from 35 µmol photons m-2 s-1 (7 mg FW) up to 500 µmol photons m-2 s-1 (27 mg FW) in female and male C. canescens. The irradiance saturation point for photosynthesis (Ek) was about 140 µmol m-2 s-1 for both sexes within the whole range of acclimation irradiances. The maximum photosynthesis rate at saturating irradiances (Pmax) of male algae was highest at Ek, whereas Pmax of female algae was highest at 500 µmol photons m-2 s-1. The photosynthetic efficiency in the light-limited range (a) increased in female C. canescens and decreased in male C. canescens. The ratio of the non-photochemical quenching parameter (NPQ) to the relative electron transport rates rETR(MT) increased in both sexes with irradiance, but showed a steeper increase in male than in female algae. Pigment analysis showed similar acclimation pattern for male and female C. canescens. Chl a/Chl b ratios of both sexes were constant over the whole range of Eg, whereas Chl a/carotenoid ratios in male and female C. canescens decreased from 70 µmol photons m-2 s-1 upwards. Pigment analysis pointed out that the carotenes a-, ß- and ?-carotene were more prominent in male than in female algae. Our results indicate that female C. canescens are more efficient in light acclimation than male algae from the same site. Nevertheless, further investigations of bisexual C. canescens populations resolving CO2-uptake mechanisms and/or genetic differences are needed.
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7 mg FW) up to 500 µmol photons m-2 s-1 (