AME 45:69-77 (2006)  -  doi:10.3354/ame045069

ABSTRACT: Simultaneous measurements of photosynthesis (PS) and bacterial biomass production (BBP) were made on floating periphyton mats using a dual-isotope radioassay (¹⁴C-bicarbonate and ³H-l-leucine). Measurements were made across a gradient of light intensity in nutrient-limited periphyton, and under saturating light in a nutrient enrichment experiment. Mean PS in nutrient-limited periphyton followed standard light-saturation kinetics, but mean BBP showed little or no relationship to light. However, individual measurements of PS and BBP were correlated when data from all light levels were combined. Laboratory experiments revealed that both N and P enrichment altered the relationship between PS and BBP. N enrichment increased average PS and BBP, but weakened the correlation between these variables. P enrichment did not statistically increase PS or BBP, but did increase the dispersion of these data in bivariate space. Although the relationship between PS and BBP in the P enrichment was weaker than the relationship observed in the control, PS and BBP remained more tightly coupled during P enrichment than in N enrichment. Results of the present study suggest that N enrichment (i.e. induced P-limitation) may have decoupled PS and BBP by causing a competitive interaction for inorganic P. P enrichment, however, may have further facilitated a cooperative relationship, whereby bacterial production depended on the supply of either photosynthetically derived extracellular organic carbon or perhaps N derived from light-dependent N₂ fixation.

KEY WORDS: Metaphyton · Algal–bacterial interaction · Nitrogen limitation · Phosphorus limitation