DISSOLVED ORGANIC SUBSTRATES AS PHOSPHORUS AND NITROGEN-SOURCES FOR AXENIC BATCH CULTURES OF FRESH-WATER GREEN-ALGAE

The growth and yields of four green algae (Pediastrum duplex Meyen, Scenedesmus sp., Tetraedron sp. and Selenastrum sp.) were examined in axenic batch cultures with either dissolved organic phosphorus (DOP) or dissolved organic nitrogen (DON) compounds as sources of phosphorus (P) or nitrogen (N), respectively. These algae, which are major components of the summer-autumn phytoplankton in Lake Kinneret, Israel, showed marked differences in growth response. Scenedesmus and Tetraedron strains grew most rapidly, with highest yields on some DOP compounds, such as ribose phosphate and ATP, whereas Pediastrum was most effective in exploiting some DON sources, such as tryptophan. These observations are consistent with the hypothesis that the differential ability of microalgae to utilize DOP and DON as P and N sources may be ecologically significant, and may play a role in determining the species composition of phytoplankton assemblages in aquatic systems.