Heterotrophic Bacteria Show Weak Competition for Nitrogen in Mediterranean Coastal Waters (Thau Lagoon) in Autumn

• Published in: Microbial ecology 2016-02, Vol.71 (2), p.304-314
• Main Authors: Trottet, Aurore, Leboulanger, Christophe, Vidussi, Francesca, Pete, Romain, Bouvy, Marc, Fouilland, Eric
• Format: Article
• Language: English
• Subjects: Ammonium; ammonium compounds; ammonium nitrogen; autumn; Bacteria; Bacteria - classification; Bacteria - genetics; Bacteria - metabolism; Biodiversity and Ecology; Biomass; Biomedical and Life Sciences; Chlorophyll; coastal water; Coastal waters; Ecology; Ecology, environment; Ecosystems; Environmental Sciences; Fractionation; Geoecology/Natural Processes; Global Changes; Lagoons; Life Sciences; Mediterranean Region; Mediterranean Sea; Microbial Ecology; Microbiology; MICROBIOLOGY OF AQUATIC SYSTEMS; Nature Conservation; nitrate nitrogen; nitrates; nitrogen; Nitrogen - analysis; Nitrogen - metabolism; Nutrient loading; Phytoplankton; Phytoplankton - classification; Phytoplankton - metabolism; pollution load; Primary production; primary productivity; Seasons; Seawater - analysis; Seawater - microbiology; stable isotopes; tracer techniques; Water Quality/Water Pollution
• ISSN: 0095-3628; 1432-184X
• DOI: 10.1007/s00248-015-0658-8

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 ¹⁵N 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.