Xanthophyceaen assemblages during winter-spring flood:: autecology and ecophysiology of Tribonema fonticolum and T monochloron

The autecology and ecophysiology of two selected periphytic species of Xanthophyceae (Tribonema fonticolum and T. monochloron) were studied from seasonal pools of the inundation area, in the upper part of the Luznice River (Trebonsko Biosphere Reserve, Czech Republic) during winter-spring flood. Our studies have shown that these species differ in their ecological requirements (their temperature and light optima; inorganic carbon sources for photosynthesis; and also their ability to survive freezing and desiccation injuries). In our experiments, the optimal growth temperatures for both strains were higher than the temperatures of the water they were collected and isolated from. Tribonema monochloron has the rate of photosynthesis several times higher than T. fonticolum. In addition, the optimal growth temperatures were about 3-4 degrees C lower for Tribonema monochloron than for T. fonticolum. From our results, we concluded that both strains of Tribonema prefer low intensities of irradiance. Both Tribonema strains were determined as CO2 users, but we revealed the ability of T. fonticolum to use HCO3- in small amounts. In both Tribonema strains, 100% of the cells survived freezing down to -4 degrees C. The cells' viability after freezing at -40, -100 and -196 degrees C was much higher for T. monochloron (about 40%) than for T. fonticolum (about 4%). With respect to desiccation damages, at temperatures of +4 and +20 degrees C, T. monochloron (the species better adapted to low temperatures) did not survive. In contrast, about 80% cells of T. fonticolum survived desiccation at both temperatures.