Photosynthetic characteristics and physiological plasticity of an Aphanizomenon flos-aquae (Cyanobacteria, Nostocaceae) winter bloom in a deep oligo-mesotrophic lake (Lake Stechlin, Germany)

In winter of 2009/2010, Aphanizomenon flos-aquae bloomed in the ice and snow covered oligo-mesotrophic Lake Stechlin, Germany. The photosynthesis of the natural population was measured at eight temperatures in the range of 2-35A degrees C, at nine different irradiance levels in the range of 0-1,320 mu mol m(-2) s(-1) PAR at each applied temperature. The photoadaptation parameter (I (k)) and the maximum photosynthetic rate (P (max)) correlated positively with the temperature between 2 and 30A degrees C, and there was a remarkable drop in both parameters at 35A degrees C. The low I (k) at low temperatures enabled the active photosynthesis of overwintering populations at low irradiance levels under ice and snow cover. The optimum of the photosynthesis was above 20A degrees C at irradiances above 150 mu mol m(-2) s(-1). At lower irradiance levels (7.5-30 mu mol m(-2) s(-1)), the photosynthesis was the most intensive in the temperature range of 2-5A degrees C. The interaction between light and temperature allowed the proliferation of A. flos-aquae in Lake Stechlin resulting in winter water bloom in this oligo-mesotrophic lake. The applied 2A degrees C is the lowest experimental temperature ever in the photosynthesis/growth studies of A. flos-aquae, and the results of the P-I and P-T measurements provide novel information about the tolerance and physiological plasticity of this species.