354
ALAIN SOURNIA
higher activity wound noon and H. minimum around midnight nearly
in plinMe uith upti~kc rates (Eppley et al., 1970), while the peak occurred
earlier in a Cowolitlms culture (Eppley et al., 1971) together with
glutantic dchydrogennse ancl opposite to nitrite reductase. For a
review of similar work on freshwater cultures, Lorenzen (1970) may be
referred to.
A genoral tendency thutJ emerges for an increasing utilization of
n i t w t e ~ n d
ammonium during daylight-which, once again, would not
surprise physiologists. No wonder if discrepancies are found from one
p p o r to another, since different8 approaches and metabolic stages
were involved tmd different onvironmental conditions were cncountered.
It rcmainls true that all the processes studied so far exhibit a diel
pcriodicity .
B . Phosphorus
'l'hc early ohervution by Newcombe and Lang (1939) of n '' pronounced iricrease shortly after dark and a marked decrease following
sunrise '' of phosphate concentration in sea water has been confirmed
by subsequent works : Newcombe and Brust (1940) in the same area,
naniely a Chesapeake eRtuar-y, Bruce and Hood (1959) in some Texas
hays and on laboratory cultures, Ryther et al. (1 961) in the Sargasso
sea, rind to some extent Sacchi et al. (1969) in Italian brackish waters;
this pilttern is also substantiated by a few measurements made by
Nerbluiid at al. (1973) in an upwelling itrea. However, Lorenzen (1963)
observed minimum contents a t 03.00 and maximum ones at 12.30,
opposite to the changes in nitrate, in an estuary a t Long Island.
It can thus be stated that phosphorus is consumed by phytoplankton
during the (lay and regenerated a t night (Bruce and H O C J ~ ,
1959).
Assimilution rates, as deduced from conccmtration chunges in the
medium, were found by Eppley el al. (1072) in their shipbortrd cultcirc+cc
to be at B minimum hetween 18.00 and 24.00 hour8 and greiLtent (luring
daylight Iiours.
An iittcmyt was recently made to evaluate the half-wtiiration
constants for phosphate uptake by lake populations during a diel stridy
(Stross et al., 1973); unfortmately, values fell below the natural
concentrations.
C. Silica
Silicate concentrations in the expcrimentv reported just above
indicatecl higher assimilation rates around noon ancl around midnight
(Eppley PI al., 1972).
CJsing a t newly developed tracer mcthotl of their own, Goering (in
ALAIN SOURNIA
higher activity wound noon and H. minimum around midnight nearly
in plinMe uith upti~kc rates (Eppley et al., 1970), while the peak occurred
earlier in a Cowolitlms culture (Eppley et al., 1971) together with
glutantic dchydrogennse ancl opposite to nitrite reductase. For a
review of similar work on freshwater cultures, Lorenzen (1970) may be
referred to.
A genoral tendency thutJ emerges for an increasing utilization of
n i t w t e ~ n d
ammonium during daylight-which, once again, would not
surprise physiologists. No wonder if discrepancies are found from one
p p o r to another, since different8 approaches and metabolic stages
were involved tmd different onvironmental conditions were cncountered.
It rcmainls true that all the processes studied so far exhibit a diel
pcriodicity .
B . Phosphorus
'l'hc early ohervution by Newcombe and Lang (1939) of n '' pronounced iricrease shortly after dark and a marked decrease following
sunrise '' of phosphate concentration in sea water has been confirmed
by subsequent works : Newcombe and Brust (1940) in the same area,
naniely a Chesapeake eRtuar-y, Bruce and Hood (1959) in some Texas
hays and on laboratory cultures, Ryther et al. (1 961) in the Sargasso
sea, rind to some extent Sacchi et al. (1969) in Italian brackish waters;
this pilttern is also substantiated by a few measurements made by
Nerbluiid at al. (1973) in an upwelling itrea. However, Lorenzen (1963)
observed minimum contents a t 03.00 and maximum ones at 12.30,
opposite to the changes in nitrate, in an estuary a t Long Island.
It can thus be stated that phosphorus is consumed by phytoplankton
during the (lay and regenerated a t night (Bruce and H O C J ~ ,
1959).
Assimilution rates, as deduced from conccmtration chunges in the
medium, were found by Eppley el al. (1072) in their shipbortrd cultcirc+cc
to be at B minimum hetween 18.00 and 24.00 hour8 and greiLtent (luring
daylight Iiours.
An iittcmyt was recently made to evaluate the half-wtiiration
constants for phosphate uptake by lake populations during a diel stridy
(Stross et al., 1973); unfortmately, values fell below the natural
concentrations.
C. Silica
Silicate concentrations in the expcrimentv reported just above
indicatecl higher assimilation rates around noon ancl around midnight
(Eppley PI al., 1972).
CJsing a t newly developed tracer mcthotl of their own, Goering (in