Trottet Aurore auteur aut IRD Leboulanger Christophe auteur aut IRD Vidussi F. auteur aut IRD Pete R. auteur aut IRD Bouvy Marc auteur aut IRD Fouilland E. auteur aut IRD text journalArticle eng text/pdf born digital access The importance of heterotrophic bacteria relative to phytoplankton in the uptake of ammonium and nitrate was studied in Mediterranean coastal waters (Thau Lagoon) during autumn, when the Mediterranean Sea received the greatest allochthonous nutrient loads. Specific inhibitors and size-fractionation methods were used in combination with isotopic N-15 tracers. NO3 (-) and NH4 (+) uptake was dominated by phytoplankton (60 % on average) during the study period, which included a flood event. Despite lower biomass specific NH4 (+) and NO3 uptake rates, free-living heterotrophic bacteria contributed significantly (> 30 %) to total microbial NH4 (+) and NO3 (-) uptake rates in low chlorophyll waters. Under these conditions, heterotrophic bacteria may be responsible for more than 50 % of primary production, using very little freshly produced phytoplankton exudates. In low chlorophyll coastal waters as reported during the present 3-month study, the heterotrophic bacteria seemed to depend to a greater extent on allochthonous N and C substrates than on autochthonous substrates derived from phytoplankton. specialized Bacteria Phytoplankton Inhibitors Size fractionation Nitrogen uptake Dissolved inorganic nitrogen FRANCE MEDITERRANEE ZONE MEDITERRANEENNE 036 71 2 304-314 2016 0095-3628 https://www.documentation.ird.fr/hor/fdi:010066165 10.1007/s00248-015-0658-8 0095-3628 [F B010066165] https://www.documentation.ird.fr/hor/fdi:010066165 https://www.documentation.ird.fr/intranet/publi/2016/02/010066165.pdf Accès réservé (Intranet de l'IRD) IRD - Base Horizon / Pleins textes 2016-02-26 2017-08-23 fdi:010066165 fre