Tf. Thingstad et H. Havskum, Bacteria-protist interactions and organic matter degradation under P-limited conditions: Analysis of an enclosure experiment using a simple model, LIMN OCEAN, 44(1), 1999, pp. 62-79
An enclosure experiment was performed in the brackish layer of a Norwegian
fjord, a system where both phytoplankton and bacterial growth have previous
ly been hypothesized to be phosphorus (p) limited. All enclosures had a suc
cession pattern characterized by an initial autotrophic phase with positive
net community production, increasing phytoplankton primary production, and
chlorophyll, followed by a heterotrophic phase with decline in primary pro
duction, negative net community production, increased community respiration
, bacterial production. and biomass. Daily additions of phosphate increased
the amplitudes of both the autotrophic and the heterotrophic phases of thi
s succession. Because no stimulating effect of glycine addition on bacteria
l production or on community respiration was observed, the delay in bacteri
al response could not easily be explained as a delay in production or avail
ability of carbon substrates for the bacteria. An alternative hypothesis is
that bacterial production is regulated by a combination of P-limited bacte
rial growth rate and predatory control of bacterial biomass. A simple numer
ical model based on this hypothesis was able to reproduce the main features
of the observed pattern of succession.