3 Algae and Nutrients: Uptake and Utilization
of Limiting Nutrients in Generalized
Phytoplankton Species
In the steady state, uptake and growth are
fully coupled, v = p Q, but that is not to imply
that growth is controlled by uptake. On the
contrary, the converse may apply ...
M. R. Droop (I 983)
In a nutrient-limited environment. a successful competitor must be able to
maintain nonnegative growth at nutrient levels less than those required by
other. competing species. The fate of a phytoplankton population is
therefore to a large extent determined by the ability of its individual
members to take up mineral nutrients from dilute solutions and the efficiency with which these nutrients are utilized to form new biomass. As
phytoplankton constitute a major food source to grazing zooplankton. the
stoichiometry of algal biomass will also affect the nutrient supply to higher
trophic levels. Although similar principles seem to apply for a range of
nutrients potentially limiting to phytoplankton growth (e.g •• p. N. Fe. Mn;
Morel 1987). the main focus in this chapter will be on the uptake and
utilization of inorganic phosphorus. either as the single limiting nutrient or
in a situation where both phosphorus and nitrogen may be limiting.
3.1 Growth and Nutrient Utilization
It is generally observed that the biomass yield in a nutrient-limited
chemostat culture is negatively correlated to dilution rate (D; dOl). and that
this relationship is fairly linear. If we define the biomass carbon yield in a
phosphorus-limited phytoplankton culture as Y [(mg C) (Jig pr l ]. the
steady-state yield can be written as
Y = Y{ 1- ;.).
(3.1)