[Buoyancy regulation and vertical distribution of Planktothrix mougeotii in the simulator experiments].

The dominance of gas-vacuolated cyanobacteria is often attributed to their buoyancy and buoyancy in response to environmental conditions. Lake simulator experiments (4 m high and 1 m diameter) and pyrex bottle experiments (10 L) were applied to investigate the buoyancy regulation and vertical distribution of Planktothrix mougeotii in eutrophic lakes at 28 degrees C. During light phase, the filaments stratify in the 2-3 m after 8 h light exposure and the biomass at the layer attach maximum after 12 h light exposure. During dark phase, the filaments are tent to migrate to the surface. 20% of filaments migrate to the surface after 12 h and 50% of filaments migrate to the surface after 48 h. The buoyancy regulation under light condition is that filaments stratify in 10 micromol x (m2 x s)(-1) layers, and the filaments above the layer sink down, while those suspended below the layer float up. The amplitude of diel changes in buoyancy is related to photon irradiance, and the change of buoyancy in light [100 micromol x (m2 x s)(-1)]/ dark is higher than its in light [25 micromol x (m2 x s)(-1)]/ dark. Carbohydrate ballasting may be the only mechanism for buoyancy changes in Planktothrix mougeotii filaments during the period.