Simultaneous use of 14C and 3H to determine autotrophic production and bacterial protein production in periphyton

A method of simultaneously quantifying photoautotrophic (algae and cyanobacteria) and bacterial production in periphyton communities by ¹⁴C-bicarbonate and ³H-leucine incorporation was investigated and applied to communities subjected to specific intensities of photosynthetically active radiation (400–700 nm). Maximum photosynthetic output (2.23 ± 0.29 (SE) g C cm^-2 h^-1) and bacterial production (0.07 ± 0.006 g C cm^-2 h^-1) occurred at the highest photon flux density (400 mol m^-2 s^-1). Over a photon flux density range of 20–400 mol m^-2 s^-1, bacterial and autotroph productivity were significantly and positively correlated (r = 0.89). Furthermore, application of 3-(3,4-dichlorophenyl)-1,1-dimethyl urea, a photosystem 11 inhibitor, to periphyton films reduced bacterial production by 46%, but it had no such effect on bacteria-only cultures. Therefore, the magnitude of bacterial production in periphyton was coupled to the photosynthesis/metabolism of algae and/or cyanobacteria.