IN-SITU BACTERIAL PRODUCTION AND GROWTH-YIELD MEASURED BY THYMIDINE, LEUCINE AND FRACTIONATED DARK OXYGEN-UPTAKE

In situ bacterial net production and growth yield were measured using thymidine, leucine incorporation and dark oxygen consumption techniques in marine enclosures and in the Bay of Aarhus. Denmark. Bacterial respiration was significantly correlated with thymidine (r2 = 0.42, P < 0.01, y = 0.12x + 0.054) and leucine (r2 = 0.45, P < 0.01, y = 0.09x + 0.043). The range of bacterial growth yield, calculated from the relationship net production/net production + respiration, was 0.07-0.77 with 74% of the observations lying in the 0.15-0.45 growth yield interval. Substrate was an important determinant of growth yields. A significant difference was found between growth yields obtained from an enclosure with added glycine (mean 0.32 +/- 0.096) and one with added inorganic nutrients (mean 0.16 +/- 0.051) (P < 0.01, t-test). Growth yield showed a weak but significant negative correlation with temperature (r2 = 0.0.35, P < 0.001, y = -0.017x + 0.52). No correlation between chlorophyll a and growth yield was found (r2 = 0.25, P > 0.05). The results suggest that thymidine and leucine techniques reflect the levels of bacterial production to better than an order of magnitude. The variations found in the growth yield support the notion that relying on fixed growth yields reduces the accuracy of estimating gross bacterial production.