Marine diatoms grown in chemostats under silicate or ammonium limitation. II. Transient response of Skeletonema costatum to a single addition of the limiting nutrient

Abstract

Skeletonema costatum was grown at different steady-state growth rates in ammonium or silicate-limited chemostats. The culture was perturbed from its steady-state condition by a single addition of the limiting nutrient, ammonium or silicate. The transient response was followed by measuring nutrient disappearance of the limiting and non-limiting nutrients at frequent time intervals. The results from a typical perturbation experiment indicate that three distinct modes of uptake of the lim, iting nutrient can be distinguished; surge uptake (Vs), internally controlled uptake (vi), and externally controlled uptake (Ve). An interpretation of these three modes of uptake is given and their relation to control of uptake of the limiting nutrient is discussed. The uptake rates of the non-limiting nutrients were shown to be depressed during the surge of the uptake of the limiting nutrient. Kinetic uptake parameters, K s and Vma x, were obtained from data acquired durin~ the externally controlled uptake segment, v e. The same Vma x value of 0.12 h-l, was obtained under either silicate or ammonium limitation. Estimates of K s were 0.4 ~gat NH4-N 1-I and 0.7 ~g-at Si 1-I. Short-term 15N uptake-rate measurements conducted on nitrogen-limited cultures appear to be a combination of v s or v i, or at lower substrate concentrations v s and v e. It is difficult to separate these different uptake modes in batch or tracer experiments, and ensuing problems in interpretation are discussed.

Variability in Nitrate Uptake Kinetics of Phytoplankton Communities in a Mediterranean Coastal Lagoon

“…Distortions in uptake curves result when the uptake rate is not constant with time during the incubation period (Conway et al, 1976;Collos, 1983;Harrison et al, 1989). This was the case in several instances in the present study, when cumulative nitrate uptake was not related to time in a linear manner (Figure 1).…”

“…Other phytoplankton groups or genera of diatoms are presented in Table 2. Figure 1 shows representative trends in cumulative nitrate uptake as a function of time, and illustrates the three known patterns of uptake for such nutrients (Collos, 1983;Harrison et al, 1989): induced (May and August), constant (November) and surge (February, June and September) uptake [the latter following the terminology of Conway et al (1976)]. This classification has been used because it has implications on the interpretation of the shape of the uptake vs. concentration curves.…”

Nutrient limitation of the bottom‐ice microalgal biomass (southeastern Hudson Bay, Canadian Arctic)1

“…This is probably because their uptake system has low substrate affinity; namely their K, values (see above) are too high to enable them to exhaust the nutrients. This low affinity could result either from constant physiological features, or from a process of "slow or fast adaptation" (sensu Droop 1974), or "shift-up and shift-down" (sensu Conway et al 1976;Harrison et al 1976) governed by the low temperature. According to our hypothesis, when the ice microalgae start growing at under-ice illumination > 7.6 PEinst m-2 s-l, their uptake system is unable to take up nutrients fast unless ambient concentrations are high.…”

Time course of uptake of inorganic and organic nitrogen by phytoplankton in the Strait of Georgia: comparison of frontal and stratified communities

“…Variations in nitrogen uptake rate Our sampling intervals were long relative to phytoplankton rapid uptake responses seen in the laboratory (Conway et al 1976, Parslow et al 1984a and the field (e.g. Glibert ) and thus we were unable to detect short term variations in uptake rate.…”