ABSTRACT
In situ incubation of water in dialysis bags allows diffusion of dissolved organic material and therefore, incubation of bacterioplankton without substrate limitations over more than 24 h. When using size-fractionated incubations one is able to directly estimate bacterial cell production. Comparing the bacterial density at the beginning and the end of the incubation by means of epifluorescence microscopy is a suitable alternative to the conventional radiolabeling techniques to estimate bacterioplankton production. Advantages of the method are: it is inexpensive and no radiotracers are necessary; and increase in bacterial density is followed over a full diel cycle rather than in short-term incubations using radiotracers. The advantages also include no substrate limitation occurs as dialysis bags allow dissolved organic matter (DOM) to diffuse across the membrane; and using different molecular weight cut-offs the relative importance of various molecular weight fractions of DOM on bacterioplankton growth can be estimated.
