Mukhanov V. Heat production by pico- and femtoplankton

In the thesis, prospectives are considered for applying the microcalorimetric approach as a tool for measuring directly the energy flows in pelagic microbial communities and, in particular, the microbial loop. Microbial processes occuring after concentrating picoplank-ton community onto a nitrocellulose membrane have been investigated experimentally and using a simulation model. On this base, the optimal protocol of preparing the samples for further microcalorimetric measurements was proposed. The first data on the picoplankton heat flux (2-75 fW/cell), entropy production rate (0,3-0,7 J/m^-3/h/К) and dissipation function (2-5 x 10^-4/h/К) were obtained. It was shown that despite extremely low live biomass concentrations in the plankton femtofraction (<0,2 µm), its heat flow rate was comparable with those measured for the picoplankton. The source of the extra heat was experimentally revealed to be hydrolysis of biopolymers owing to bacterial extracellular activity rather than metabolism of ultramicrobacteria. The results obtained confirm that the microcalorimetric approach is highly prospective for studying energy flows in aquatic microbial communities.