Influence of bacterial activities on nitrogen uptake rates determined by the application of antibiotics
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Date
2003
Journal Title
Journal ISSN
Volume Title
Publisher
Oceanologia
Abstract
The influence of bacterial activities on inorganic nutrients has always affected total
phytoplankton uptake rates owing to the absence of a reliable method that can
exclude these effects. The use of natural samples to determine the contribution
of bacterial activities has been based on the size fractionation method which,
unfortunately, is encumbered with uncertainties, especially because of the size
overlap between bacteria and phytoplankton communities. In this paper, the
results are reported of an estimation of bacterial activities by the use of inhibitors
(antibiotics). It was shown that the contribution of bacterial activities to the
uptake of nitrogenous nutrients was highest for ammonium (79%), followed by
nitrate (72%) and urea (62%). In a second set of experiments the concentration of
ammonium was raised by 5 μM. This was done to avoid nutrient limitation resulting from the absence of recycled nutrients following the addition of antibiotics and
the maximum contribution of bacterial activity to the uptake rate of ammonium
increased to 87%. It can be concluded that the use of inhibitors is a good method,
a reliable alternative to the fractionation method. However, it is important to note
that inhibitors can affect both phytoplankton growth and the nutrient recycling
process. Our results indicate that the application of antibiotics had measurable
effects not only on the target bacteria but also on the uptake behaviour of
phytoplankton. Our observations were therefore limited to the period when there
was no effect on the phytoplankton, as was demonstrated by a carbon protein
incorporation experiment.
Description
Journal Article
Keywords
Bacteria, Phytoplankton, Nitrogenous nutrients, Uptake rates