UIRCADIAN PERIODTOITIES TN PHYTOPLANKTON
36 1
(the in situ measiirements reported a few lines above do not at all
confirm T’anoiisc’s hypothesis).
NeverthclcHs the infrequent, or merely incidental occurrence of an
uftmnoon deprerrsion in the iintural course of phytoplankton photogynthesis, ns compared to the ‘‘ compulsory ” rhythm observed under
constant, light, and compared to the bulk of aquatic and terrestrial
plants, is a challenging problem. Turbulence, which permits both the
renewal of cells at a given light level and the renewal of medium around
tho cells, may still have some effect when plankton samples are enclosed in bottles for a few hours, and is expected to play a considerable
r6le in the actual metabolism of unenclosed communities (Verduin,
1957; Ohle, 1958, 1961). Thc main point, of course, is light and the
main trouble concerns the existence and significance of light adaptation.
Photosynthetic efficiency, i.e. photosynthesis per unit of biomass and
unit of light energy, is known to undergo diel changes (Goldman et al,,
1969; Kalff, 1969) as does the optimum light intensity (Kdff, 1969;
see also Jrargensen, 1966 or Steemann Nielsen and Jlzrrgensen, 1968).
A closely related phenomenon is light inhibition in surface waters
around noon (Marshall and Orr, 1928 ; Kurasige, 1932 ; Jenlrin, 1937 ;
ichimuru, 1958; Occhipinti et al., 1961; Panouse, 1972 aqd others)
which become8 particularly evident in arctic and antarctic seas and
lakes during their respective summtm (El-Sayed and Mandelli, 1965 :
Goltlrnan et a,?., 1969; Kalff, 1969).
Because thc picture is so complex, thc choiec of a suitable sampling
time for in situ meusurements is a11 arduous problem; any proposed
solution (eg. Panouse, 1972 ; Capblnncq, 1972) can only have a restricted
application, as was the case with photoaynthetic capacity. As for the
meaning of dtdy production (the protluction for a whole day, night
included or not), it depends both on preambles and technique#, juNt
like the significnnce of annual production.
X. REYPIRAT[ON
Little--or nothing-is known about diel variations of respiration,
~1 topic which has been barely npproached by a few oceanographers
(Doty and Oguri, 1957; Ryther et al., 1958) or limnologista (Verduin,
1957: Vollenweider and Nauwerck (1961). As a matter of fact, the
knowledge of both mitochondria1 respiration and photorespiration in
planktonic algae still remains at an elementary stage.
However, itl seeins established in the field of algal physiology that
dark respiration undergoes a persistent circadian rhythm, roughly
o1)posite to phot,osynthetic capacity, the peak occurring a t the beginning
or middle of the dark phaee : see e.g. the works of Pimon et ctE. (1954) and
36 1
(the in situ measiirements reported a few lines above do not at all
confirm T’anoiisc’s hypothesis).
NeverthclcHs the infrequent, or merely incidental occurrence of an
uftmnoon deprerrsion in the iintural course of phytoplankton photogynthesis, ns compared to the ‘‘ compulsory ” rhythm observed under
constant, light, and compared to the bulk of aquatic and terrestrial
plants, is a challenging problem. Turbulence, which permits both the
renewal of cells at a given light level and the renewal of medium around
tho cells, may still have some effect when plankton samples are enclosed in bottles for a few hours, and is expected to play a considerable
r6le in the actual metabolism of unenclosed communities (Verduin,
1957; Ohle, 1958, 1961). Thc main point, of course, is light and the
main trouble concerns the existence and significance of light adaptation.
Photosynthetic efficiency, i.e. photosynthesis per unit of biomass and
unit of light energy, is known to undergo diel changes (Goldman et al,,
1969; Kalff, 1969) as does the optimum light intensity (Kdff, 1969;
see also Jrargensen, 1966 or Steemann Nielsen and Jlzrrgensen, 1968).
A closely related phenomenon is light inhibition in surface waters
around noon (Marshall and Orr, 1928 ; Kurasige, 1932 ; Jenlrin, 1937 ;
ichimuru, 1958; Occhipinti et al., 1961; Panouse, 1972 aqd others)
which become8 particularly evident in arctic and antarctic seas and
lakes during their respective summtm (El-Sayed and Mandelli, 1965 :
Goltlrnan et a,?., 1969; Kalff, 1969).
Because thc picture is so complex, thc choiec of a suitable sampling
time for in situ meusurements is a11 arduous problem; any proposed
solution (eg. Panouse, 1972 ; Capblnncq, 1972) can only have a restricted
application, as was the case with photoaynthetic capacity. As for the
meaning of dtdy production (the protluction for a whole day, night
included or not), it depends both on preambles and technique#, juNt
like the significnnce of annual production.
X. REYPIRAT[ON
Little--or nothing-is known about diel variations of respiration,
~1 topic which has been barely npproached by a few oceanographers
(Doty and Oguri, 1957; Ryther et al., 1958) or limnologista (Verduin,
1957: Vollenweider and Nauwerck (1961). As a matter of fact, the
knowledge of both mitochondria1 respiration and photorespiration in
planktonic algae still remains at an elementary stage.
However, itl seeins established in the field of algal physiology that
dark respiration undergoes a persistent circadian rhythm, roughly
o1)posite to phot,osynthetic capacity, the peak occurring a t the beginning
or middle of the dark phaee : see e.g. the works of Pimon et ctE. (1954) and