Incidence of phytoplankton and environmental conditions on the bacterial ammonium uptake in a subtropical coastal lagoon

Publicado en Journal of Limnology, v. 73(1):122-130

Pérez, G., Farías, L., Fernandez, C., Conde, D. and Piccini, C.

Año de publicación 2014
  • Instituto de Investigaciones Biológicas Clemente Estable, Uruguay.
  • Universidad de Concepción, Chile.
  • UPMC Univ. Paris 06 and CNRS, UMR 7621, France.
  • Universidad de la República, Uruguay.
  • Instituto de Investigaciones Biológicas Clemente Estable, Uruguay.


Proyecto CRN3070


We analyzed the coupling between bacterioplankton and phytoplankton in Laguna de Rocha through an experimental approach. A freshwater zone of high turbidity and macrophytes growth and a brackish zone of higher light penetration and lower macrophytes biomass characterize this coastal lagoon. It has been shown that dissolved inorganic nitrogen, especially NH4+, has decreased to undetectable levels during the last decade. One hypothesis for this trend is the rapid removal by phytoplankton and bacterioplankton uptake. In an attempt to test this, we performed incubations using lagoon water from both zones split in two treatments (pre-filtered by 1.2 µm and unfiltered water) and amended with 15N-NH4+. After 4 h incubation we found that in both zones bacterioplankton showed significantly higher NH4+ uptake rates when incubated together with phytoplankton and that uptake rates of both microbial communities were higher in freshwater incubations. These results suggest that bacterial NH4+ uptake would be coupled to phytoplankton-derived exudates and hence that depletion of dissolved NH4+ in this system could be linked to rapid microbial uptake. The degree of this coupling would vary according to hydrological dynamics in this ecosystem.