The freshwater red alga Batrachospermum turfosum (Florideophyceae) can acclimate to a wide range of light and temperature conditions

Batrachospermum turfosum Bory is one of the generalists among the few red algae that have adapted to freshwater habitats, occurring in a variety of primarily shaded, nutrient-poor micro-habitats with lotic (running) or lentic (standing) waters. Seasonal variations in water level and canopy cover can expose this sessile alga to widely fluctuating temperatures, solar irradiation and nutrient availability. Here we report on the ecophysiology of B. turfosum collected from an ultra-oligotrophic bog pool in the Austrian Alps. Photosynthesis as a function of photon fluence density (PFD) and temperature was studied by measuring oxygen evolution in combination with chlorophyll fluorescence. In addition, the effects of ultraviolet radiation (UVR) on photosynthetic pigments were analysed using HPLC and spectrophotometric methods, and cellular ultrastructure was studied using transmission electron microscopy. We found that B. turfosum is adapted to low light, with a light compensation point (I_c) and a light saturation point (I_k) of 8.4 and 29.7 µmol photons m^–2 s^–1, respectively, but also tolerates higher PFDs of ~1000 µmol photons m^–2 s^–1, and is capable of net photosynthesis at temperatures between 5°C and 35°C. Exposure to either UV-A or UV-AB for 102 h led to a strong transient drop in effective quantum yield (ΔF/F_M’), followed by an acclimation to about 70% of initial ΔF/F_M’ values. Ultrastructural changes included the accumulation of plastoglobules and dilated membranes after UVR treatment. Although all photosynthetic pigments strongly decreased upon UVR exposure and no UV-photoprotectants (e.g. mycosporine-like amino acids) could be detected, the alga was capable of recovering ΔF/F_M’ and phycobiliproteins after UVR treatment. In summary, B. turfosum tolerates a wide range of irradiation and temperature regimes, and these traits may be the basis for its successful adaptation to challenging environments.