SIMULTANEOUS USE OF C-14 AND H-3 TO DETERMINE AUTOTROPHIC PRODUCTION AND BACTERIAL PROTEIN-PRODUCTION IN PERIPHYTON

A method of simultaneously quantifying photoautotrophic (algae and cya nobacteria) and bacterial production in periphyton communities by C-14 -bicarbonate and H-3-leucine incorporation was investigated and applie d to communities subjected to specific intensities of photosynthetical ly active radiation (400-700 nm). Maximum photosynthetic output (2.23 +/- 0.29 (SE) mu g C cm(-2) h(-1)) and bacterial production (0.07 +/- 0.006 mu g C cm(-2) h(-1)) occurred at the highest photon flux density (400 mu mol m(-2) s(-1)). Over a photon flux density range of 20-400 pmol m(-2) s(-1), bacterial and autotroph productivity were significan tly and positively correlated (r = 0.89). Furthermore, application of 3-(3,4-dichlorophenyl)-1,1-dimethyl urea, a photosystem II inhibitor, to periphyton films reduced bacterial production by 46%, but it had no such effect on bacteria-only cultures. Therefore, the magnitude of ba cterial production in periphyton was coupled to the photosynthesis/met abolism of algae and/or cyanobacteria.