nitrate appears to act as an alternate hydrogen acceptor in photosynthesis(round,1965).when chlorella is grown in the light with glucose and nitrate but with no available co2,it gives off oxygen,which indicates reduction of nitrate.closed system marine aquariums with zooxanthellate corals and/or large standing stocks of algae may have little available co2 when brightly illluminated.under such circumstances the algae may effectively reduce nitrate concentrations in the aquarium.