Aquatic Sciences Meeting (Aquatic Sciences: Global And Regional Perspectives - North Meets South), 22-27 February 2015, Granada, Spain.Microcosm experiments to assess bacterioplankton response to autochthonous inputs of organic matter modified by future acidified ocean conditions were performed. Surface seawater enriched with inorganic nutrients and incubated in UVR-transparent cubitainers was bubbled for 8 days with regular air (380 ppmv CO2) or with a high CO2-air mixture (1000 ppmv CO2) to be used as inocula. In the second phase of the experiment, natural bacterioplankton communities enriched with the acidified or non-acidified organic matter inocula were incubated under dark conditions during 8 days in the presence or absence of CO2 as previously. Bacterial abundance, production and viability were measured as physiological indicators of bacterial metabolism. The results showed that acidified organic matter produced higher abundances for similar production rates early during the incubation, while non-acidified organic matter produced higher bacterial production and viability latter at the end of the experiment, indicating a more recalcitrant character of the organic matter under these conditions. We demonstrate that CO2 effects on bacterioplankton are mainly due to indirect effects on organic matter characteristics rather than to direct effects of acidification on bacteria metabolism.N
