(^) Under steady-state conditions, the nutrient uptake rate is equal to the product of the specific growth
rate and the cellular quota:
(^) and this steady nutrient uptake is observed to follow a hyperbolic function of the external nutrient
concentration (using ρssmax and kμQ for distinction from ρmax and kρ:
(^) Morel (1987) describes the derivations and applications in more detail.
(^) Both the Monod and Droop equations have been useful for the study of nutrient uptake and growth
kinetics for cultured phytoplankton under steady-state conditions. The Monod model is simpler and
preferred for steady-state conditions, while the Droop model is more complex and has the additional
requirement of determining the variations in cell quota but it performs better under transient
conditions.
Chan’s (1978) data (Fig. 3.11) show that fully photoacclimated dinoflagellates
typically reach maximal doubling rates at lower irradiance than diatoms, while
diatoms have higher maximum growth rates. Actually, dinoflagellates and diatoms
have the same photosynthetic rates per unit chlorophyll, but autotrophic
dinoflagellates have much less chlorophyll relative to other cell constituents. When
adapted to high irradiance, >200 μmol photons m−2 s−1, typical dinoflagellates have 4
to 10 ng Chl (μg protein)−1, whereas diatoms have 15 to 30 ng Chl (μg protein)−1.
Dinoflagellates also have a much more DNA than other algae, and consequently
require more energy for cellular maintenance, giving them a lower growth efficiency
(Tang 1996).
Fig. 3.11 Response of growth rates to changes in irradiance compared for diatoms
(left) and dinoflagellates (right). These are exponential rates established after long
acclimation at each irradiance. Bars are 95% confidence limits.
(^) (After Chan 1978.)
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