Strategies providing success in a variable habitat: II. Ecophysiology of photosynthesis of Cladophora glomerata

Cladophora glomerata (L.) Kutz. is the dominant filamentous algae of the ri ver Ilm, Thuringia, Germany. For most of the year it can be found at open a s well as at shaded sites. Photosynthetic acclimation of C. glomerata to di fferent light intensities was detected by chlorophyll fluorescence measurem ents and pigment analysis. Cladophora glomerata from highlight sites showed decreased values of efficiency of open photosystem II (F-v/F-m) as compare d with C. glomerata from low-light sites. Winter populations revealed highe r F-v/F-m values than summer populations. A light-induced decrease in effic iency of the closed photosystem II was observed at increasing irradiance in tensities. The decrease was higher in C, glomerata from shaded sites compar ed with plants from open sites. Differences in the photosynthetic electron transport rate of different populations of C. glomerata were shown by photo synthesis-irradiance curves. Summer populations from high-light sites yield ed higher maximum electron transport rates than plants from low-light Sites , whereas winter populations exhibited significantly decreased values compa red with the summer populations. Results of the analysis of photosynthetic pigments corresponded,vith data from chlorophyll fluorescence measurements. In addition to these long-term acclimation effects, C. glomerata expressed its ability to cope,vith rapid changes in the light environment by the dee poxidation of violaxanthin during exposure to high light intensities.