122
E. D. 9. CORNER AND ANTHONY Q. DAVIES
( 1965) have demonstrated that under phosphate-deficient conditions,
the enzyme alkaline phosphatase is produced within phytoplankton
cdls ; but that when external phosphate concentrations are adequate
for growth, formation of the enzyme is suppressed. This enzyme has
the ability to hydrolyse organic phosphate esters, and it was shown
that its presence within cells enables them to utilize the phosphate
portion of such esters. The rate of uptake of phosphate from tlirce
different types of ester (glucose-6-phosphate, adenosine monophosphate
and a-glyceropliospliate) was found to be the same for a given phytoplankton species, indicating that a similar uptake mechanism was
operating for all three compounds. Apparently only the phosphate
portion was absorbed by the cells, the organic portion remaining in the
culture medium. This probably indicates that the site of action of the
enzyme was on or near the exterior surface of the cells.
Although the organic forms of phosphorus in the sea remain to be
identified, some will almost certainly be present as phosphate esters.
Kuenzler and Perras (1965) have suggested that the ability of
phosphate-deficient phytoplankton to utilize this source of the nutrient
could be of considerable importance: for the rate at which phosphate
can be recycled in the euphotic zone would be greatly increased if
complete remineralisation were unnecessary. However, the levels of
enzyme-hydrolysable organic phosphate found by Strickland and
SolGrzano (1966) in coastal waters were very low (0.03-0.45 pg-atoms
P/l), though this could have been due to rapid utilization of these
phosphate esters.
The quantitative relationship between the rate of phosphate uptake
by phytoplankton and the concentration of the nutrient in sea water has
yet to be established ; but the early work of Ketchum (19394 indicates
that it is also hyperbolic in form. Interestingly, this work demonstrated that phosphate uptake rates are also hyperbolically related to
the nitrate concentration of the medium.
VI. THE EFFECT OF NUTRIENT LEVELS ON PHYTOPLANKTON GROWTH
KINETICS
Although the comparative growth rates of various phytoplankton
species under nutrient limiting conditions are likely to have a great bearing upon seasonal variations in the species composition of the phytoplankton, the quantitative relationship between the division rate of
the phytoplankton population and the available nutrient concentration
is not, at present, well defined. Insome cases, an equationhaving the same
form as that described for uptake appears to hold : Eppley and Thomas
(1969), for instance, have shown that the growth rates of Asterionella
E. D. 9. CORNER AND ANTHONY Q. DAVIES
( 1965) have demonstrated that under phosphate-deficient conditions,
the enzyme alkaline phosphatase is produced within phytoplankton
cdls ; but that when external phosphate concentrations are adequate
for growth, formation of the enzyme is suppressed. This enzyme has
the ability to hydrolyse organic phosphate esters, and it was shown
that its presence within cells enables them to utilize the phosphate
portion of such esters. The rate of uptake of phosphate from tlirce
different types of ester (glucose-6-phosphate, adenosine monophosphate
and a-glyceropliospliate) was found to be the same for a given phytoplankton species, indicating that a similar uptake mechanism was
operating for all three compounds. Apparently only the phosphate
portion was absorbed by the cells, the organic portion remaining in the
culture medium. This probably indicates that the site of action of the
enzyme was on or near the exterior surface of the cells.
Although the organic forms of phosphorus in the sea remain to be
identified, some will almost certainly be present as phosphate esters.
Kuenzler and Perras (1965) have suggested that the ability of
phosphate-deficient phytoplankton to utilize this source of the nutrient
could be of considerable importance: for the rate at which phosphate
can be recycled in the euphotic zone would be greatly increased if
complete remineralisation were unnecessary. However, the levels of
enzyme-hydrolysable organic phosphate found by Strickland and
SolGrzano (1966) in coastal waters were very low (0.03-0.45 pg-atoms
P/l), though this could have been due to rapid utilization of these
phosphate esters.
The quantitative relationship between the rate of phosphate uptake
by phytoplankton and the concentration of the nutrient in sea water has
yet to be established ; but the early work of Ketchum (19394 indicates
that it is also hyperbolic in form. Interestingly, this work demonstrated that phosphate uptake rates are also hyperbolically related to
the nitrate concentration of the medium.
VI. THE EFFECT OF NUTRIENT LEVELS ON PHYTOPLANKTON GROWTH
KINETICS
Although the comparative growth rates of various phytoplankton
species under nutrient limiting conditions are likely to have a great bearing upon seasonal variations in the species composition of the phytoplankton, the quantitative relationship between the division rate of
the phytoplankton population and the available nutrient concentration
is not, at present, well defined. Insome cases, an equationhaving the same
form as that described for uptake appears to hold : Eppley and Thomas
(1969), for instance, have shown that the growth rates of Asterionella