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 technique s in marine enclosures and in the Bay of Aarhus. Denmark. Bacterial re spiration 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 rela tionship net production/net production + respiration, was 0.07-0.77 wi th 74% of the observations lying in the 0.15-0.45 growth yield interva l. Substrate was an important determinant of growth yields. A signific ant difference was found between growth yields obtained from an enclos ure with added glycine (mean 0.32 +/- 0.096) and one with added inorga nic nutrients (mean 0.16 +/- 0.051) (P < 0.01, t-test). Growth yield s howed a weak but significant negative correlation with temperature (r2 = 0.0.35, P < 0.001, y = -0.017x + 0.52). No correlation between chlo rophyll a and growth yield was found (r2 = 0.25, P > 0.05). The result s suggest that thymidine and leucine techniques reflect the levels of bacterial production to better than an order of magnitude. The variati ons found in the growth yield support the notion that relying on fixed growth yields reduces the accuracy of estimating gross bacterial prod uction.