34ti
ALAIN SOURNIA
It wtte ROO^ recognized by lJot,y ( 1 959) that the amplitude of the
cycle wiis inversely rorrelatd with the latitude of the sampling station ;
compiling thc tlattL avsilublc a t thrit time, Doty was able to plot a
provisionid ourvo on which mitx/min rutios decreased from 10 (equator)
to 1 (tbrounr~ hat. 75”). In t h ? tLiithor’H opinion, 11s it set?nis, this wits
relnted to the frtot thtit, the IieaIcr is t)hc quator, the morc: constant
is tho de8.ylength t,ht-oughout tho your, and tho shortcr are the twilights
and d~wiis, thus the more prouounoed is tho “ pulsing effect ”. Such
a lutitudinnl varitition, though less distinct, was confirmed by Jitts
(Imr,). Furtliermoro, monsurcments repeated throughout one year at
(I fixed &ition showed that daylength rather than latitude is involved
(Lorenxen, 1963 ; Nee ~ l s o some indications of seasonal variations in
Endo, 1967, 1070); Lorenzen in his turn compiled the available data
and plotted innx/min ratios against daylength (instead of latitude) :
the rutio is the higher (up to 8) for 12-hour days and the lower (around
2) for 15-how ones. Lorenzen (1963) also suggested a symmetrical
decrcusc for daylengths shorter than 12 hours; this point is aubstantiated by a series of stations in the Indian ocean (Sournia, unpubl.), so
that t’he following relation c m definitely be postulated : the amplitude
of Doty rmd Oguri’s rhythm, a8 measured by the maximin ratio, is
higher (up to 10) when the lengths of day and night are equal; it
decreases (down to 1) as much as these two lengths differ from each
other.
The rbrnplitude may also depend on daily illumination. Lorenzen
(1963) obnerved that, for a given claylongth, the amplitude was lower
for clays of higher rdLition ; $his requires confirmation.
I h t y and Oguri’s rhythm will not be confmed with the apparent
periodicity 01’ “ pseudo-rhythm ” (Sournia, 1973) which arisee when
photosynthesis is measured by the eo-called “ simulated in aitu ” 14C:
technique (in this way, samples arc incubated for 24 hours on deck
under nuturctl illumination, light filters “ simulating ” the photometric
levels at thc? reRpectivc? depths). In this case, samples taken in the
morning re~lult in a lower ctwbon uptake than those originating from
early night (Ryther and M e n d , 1961 : Ryther el al., 1961 ; Doty et al.,
1967; Newhorisr el d . , 1967; Sournia, 1973; see also Margalef, 1972,
Table 2). This periodicity merely reflects n differential loss of labelled
carbon through nocturnal respiration (Steemann Nielsen, 1964) and it
is not, surprising if its phase is nearly opposite to the previous one
(Sourniti, 1973). In this connection it may be noted that Ohle (1958),
using tire oxygen method and 24-hour ( 1 ) incubations, obtained slightly
higher produ~t~ion in morning samples than in evening ones, but the
experimental procedure is not, reported clearly.
ALAIN SOURNIA
It wtte ROO^ recognized by lJot,y ( 1 959) that the amplitude of the
cycle wiis inversely rorrelatd with the latitude of the sampling station ;
compiling thc tlattL avsilublc a t thrit time, Doty was able to plot a
provisionid ourvo on which mitx/min rutios decreased from 10 (equator)
to 1 (tbrounr~ hat. 75”). In t h ? tLiithor’H opinion, 11s it set?nis, this wits
relnted to the frtot thtit, the IieaIcr is t)hc quator, the morc: constant
is tho de8.ylength t,ht-oughout tho your, and tho shortcr are the twilights
and d~wiis, thus the more prouounoed is tho “ pulsing effect ”. Such
a lutitudinnl varitition, though less distinct, was confirmed by Jitts
(Imr,). Furtliermoro, monsurcments repeated throughout one year at
(I fixed &ition showed that daylength rather than latitude is involved
(Lorenxen, 1963 ; Nee ~ l s o some indications of seasonal variations in
Endo, 1967, 1070); Lorenzen in his turn compiled the available data
and plotted innx/min ratios against daylength (instead of latitude) :
the rutio is the higher (up to 8) for 12-hour days and the lower (around
2) for 15-how ones. Lorenzen (1963) also suggested a symmetrical
decrcusc for daylengths shorter than 12 hours; this point is aubstantiated by a series of stations in the Indian ocean (Sournia, unpubl.), so
that t’he following relation c m definitely be postulated : the amplitude
of Doty rmd Oguri’s rhythm, a8 measured by the maximin ratio, is
higher (up to 10) when the lengths of day and night are equal; it
decreases (down to 1) as much as these two lengths differ from each
other.
The rbrnplitude may also depend on daily illumination. Lorenzen
(1963) obnerved that, for a given claylongth, the amplitude was lower
for clays of higher rdLition ; $his requires confirmation.
I h t y and Oguri’s rhythm will not be confmed with the apparent
periodicity 01’ “ pseudo-rhythm ” (Sournia, 1973) which arisee when
photosynthesis is measured by the eo-called “ simulated in aitu ” 14C:
technique (in this way, samples arc incubated for 24 hours on deck
under nuturctl illumination, light filters “ simulating ” the photometric
levels at thc? reRpectivc? depths). In this case, samples taken in the
morning re~lult in a lower ctwbon uptake than those originating from
early night (Ryther and M e n d , 1961 : Ryther el al., 1961 ; Doty et al.,
1967; Newhorisr el d . , 1967; Sournia, 1973; see also Margalef, 1972,
Table 2). This periodicity merely reflects n differential loss of labelled
carbon through nocturnal respiration (Steemann Nielsen, 1964) and it
is not, surprising if its phase is nearly opposite to the previous one
(Sourniti, 1973). In this connection it may be noted that Ohle (1958),
using tire oxygen method and 24-hour ( 1 ) incubations, obtained slightly
higher produ~t~ion in morning samples than in evening ones, but the
experimental procedure is not, reported clearly.