Revisited phytoplanktonic carbondependencyof heterotrophic bacteria in freshwaters, transitional, coastal and oceanicwaters

phytoplankton and bacteria interactions; production; carbon coupling; exudates; aquatic systems. Positive relationships between heterotrophic bacteria and particulate phytoplank-ton production (respectively, BP and PPP) have been reported for several areas, suggesting that material produced by phytoplankton was a major substrate for bacterial growth. Since then, thousands of simultaneous measurements of both PPP and BP have been performed. A review of these data showed that BP may exceed PPP considerably (median ranged between 132 % and 484%) in all aquatic systems with the lowest PPP. In oceanic waters, BP did not seem to be temporally synchronized with PPP and the median BP: PPP ratio is 15 % with moderate PPP, but the immediate bacterial carbon (C) demand (including bacterial respiration) was greater than the corresponding total primary production (i.e. dissolved and particulate primary production) for 4 80 % of both volumetric and areal datasets. In freshwaters, the strong covariation observed between BP and PPP seemed mainly due to a common response to sudden nutrient inputs into enclosed systems, leading to a similar range of production rates and temporal synchroni-cities. Indeed, phytoplankton exudates contributed directly to only 32 % (median) of BP when C-tracking experiments were performed in freshwaters. Therefore, because direct C dependency of bacteria on phytoplankton is questionable, other C sources might be more significant for bacterial growth