Is the GDH/RNH4+ ratio in the mesozooplankton constant through different oceanic systems?

[EN] Nitrogen (N) is essential for life, but its availability is frequently limited in ocean ecosystems. Among all the compounds which influence the N pool, ammonium (NH4+) represents the major source of N for autotrophs. This NH4+ is provided by bacterial remineralization and heterotrophic grazers, with the mesozooplankton responsible for 12% to 33% of the total NH4+ recycled.  Quantifying the excretion physiology of zooplankton is then, necessary to understand the basis of an aquatic ecosystem’s productivity.<br />The measurement of glutamate dehydrogenase (GDH) activity has been widely used to assess the NH4+ excretion rates in planktonic communities. However, its relationship with the physiology varies with temperature and the nutritional status of the organisms, among other variables. Here we compare the GDH/RNH4+ ratio between oceanic regions with different trophic conditions.  Strengthening our knowledge of the relationship between GDH activities and the NH4+ excretion rates will lead to more meaningful interpretations of the mesoscale variations in planktonic NH4+ excretion.