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Oseana, Volume XXIII, Nomor 2, 1998 : 19 - 25
ISSN 0216 - 1877
PHYTOPLANKTON QUANTUM YIELD AND
PIGMENT-SPECIFICATTENUATION
Oleh
Deddy Setiapermana *)
ABSTRAK
Tinjauan pustaka mengenai 'quantum yield ( ф ) yang merupakan ukuran dari
tingkat efisiensi perubahan energi cahaya menjadi energi kimiawi melalui proses
fotosintesis pada fitoplankton disajikan secara singkat. Untuk memperkirakan 'quantum yield' diperlukan informasi mengenai 'chlorophyll-specific light attenuation'
( ε ). Karenanya, uraian mengenai ε disajikan pula berdasarkan penelusuran beberapa
pustaka terpilih.
BANNISTER (1974a) believed that
фmax is 0.06 within a factor smaller than 1.5.
He considered several factors that can lower
time-average value for the фmax. First.
observed quantum yield and action spectra indicate that some phytoplankton accessory pigments (e.g. carotenoids) sensitize photosynthesis less efficiently than does chlorophyll; these
indicate that the average spectral yield is commonly 10 to 20% less than that at wave length
absorbed solely by chlorophyll. Secondly, studies of synchronous algal cultures show [hat the
maximum quantum yield is depressed during
part of he dark period; asynchrony in natural
phytoplankton could lead to a lime-average
yield 10 to 20% less than that characteristic of
the light period. Thirdly, the yield for
carbon is likely to be about 85% of the yield
of oxygen, as a result of nitrate reduction and
the formation of some carbon compunds
more reduced than carbohydrate.
INTRODUCTION
The efficiency of the conversion of light
energy into chemical energy through photosynthesis is usually expressed as quantum yield
( ф ) or quantum requirement (1/ф) or energy
efficiency. Energy efficiency of a photochemical process is generally less than the quantum
yield due to its strong wavelength dependence
(RADMER and KOK, 1977). As defined by
physiologists (see KOK. 1960), the quantum
yields is the ratio of the rate of the
photosynthesis (in moles of oxygen evolved
or of carbon incorporated per unit time) and
the rate (in quanta or Einstein absorbed per
unit time) at which light 1 s absorbed by the
phytoplankton. Plant physiologists seem to
agree on a maximum quantum yield (фmax) of
0.1 to 0.125 (see KOK, 1960; GOVINDJEE
et al., 1968; NG and BASSHAM. 1968;
RABINOWlTCH and GOVINDJEE, 1969).
*)
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Oseana, Volume XXIII no. 2, 1998
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quantum yield is at constant level. In some
cases TILZER also found the variations of
quantum yield with depth, and suggested that
such variations may be due I o the vertical shift
of light-shade adaption, susceptihlity to light
inhibition, and systematic error in estimates of
chlorophyll attenuation coefficient. Low light
adaptation has been shown to increase the susceptibility to surface light inhibition (TILZER.
1973; TILZER and GOLDMAN, 1978).
DUBINSKY el al. (1984) and ATLAS and
BANNISTER (1980) have shown that
chlorophyll attenuation coefficient varies with
depth and cannot be assumed constant.
Concerning temporal variations of
quantum yield, TILZER (1984) observed that
the general vertical pattern of quantum yield
was roughly consistent in the courses of a
single day, although a wide diurnal variability
in light-limited quantum yield axisted.
TILZER (1984) also attempted to define formula of PB as a function of ф έ (wavelengthaveraged extinction coefficient), and I
(irradiance). Further, he defined the
relationship between initial slope of
photosynthesis-irradiance (P-I) curve, α B and
quantum yield, as
REVIEW ON QUANTUM YIED ( ф )
STUDIES
MOREL (1978) adopted average
phytoplankton attenuation coefficient of
0.015 HT] (mg Chl-a m-3)-1 for calculating
quantum yield of SCOR and CINECA
expedition data. He found that the values of
quantum yield increased with decreasing
available energy; lower values was observed
in blue or blue-green waters than those in
green eutrophic waters. The highest values
were derived from the greenest waters. In
several cases, at the bottom of the euphotic
zone, the quantum yield seemed to have
values approaching 0.125.
DUBINSKY and BERMAN (1976,
1981) estimated quantum yield in Lake
Kinneret, and found quantum yield increased
with decreasing light and a maximum value of
0.07 was derived from a deep layer where PEI
(photosynthetic effective irradiance) is
reduced to 0.03% of its surface layer, probably
because the photosynthetic reaction centres
became saturated by photon flux. They used
an assumed constant chlorophyll attenuation
coefficient of 0.067 to calculate quantum
yield,
which
may
be
somewhat
underestimated for upper water column and
overestimated towards the lower depths.
TYLER (1975), MOREL (1978) and
TAGUCHI (1979) results also show the increase of quantum yield with decreasing light.
However, different result was reported by
TILZER et al. (1975) who measured quantum
yield in Lake Tahoe: he found constant levels
of quantum yield throughout the water
column. Later, TILZER (1984) studied the
vertical and temporal variations of quantum
yields in Lake Constance and observed constant vertical values of quantum yield when
thermal stability was absence. At low thermal
stability vertical mixing is generated, thus preventing light inhibition to occur. Under this
condition light is limited and photosynthetic
rates vary proportionally with light, hence
α B = 12 фmax . έ
BANNISTER and WEIDEMANN
(1984) estimated фmax.έ from the
proportionally between light-limited
photosynthesis and scalar quantum irradiance.
In a logarithmic graph of I and PB against
depth, proportionality between PB and I is
manifest by parallelsm of the two functions.
From the distance 6 between the functions, the
value of фmax is calculable. Figure 1 gives an
illustration of their estimation technique. Their
estimated value of фmax.έ for lrondequoit Bay,
corrected for respiration and other factors, was
0.00042. They also attempted to determine the
spectral distribution of έ from absorption spectrum of suspension measured by using opal
glass cuvette. Their calculated valus of έ was
P
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0.007 (550nm), 0.022 (675 nm), and 0.010
(550 - 650 nm). The everage chlorophyll attenuation coefficient, έ, was calculated to be
0.010. Based on фmax.έ = 0.00042. The quantum yield was relatively low (0.04). By using
similar technique, BANNISTER and
WEIDEMANN (I984) calculated the values
фmax.έ and фmax. from the results of
DUBINSKY and BERMAN (19761,
TAKEMATSU et al. (1981), PLATT and
JASBY (1976). Data of DUBINSKY and
BERMAN (1976) had only one single
observation lies in the range of light-limited
uptake, so proportionality was not demonstrated. For this single point, employing έ =
0.007 (DUBINSKY and BERMAN 1981) and
correcting for discrepancy between cosine and
scalar irradiance calculated value of фmax.έ
0.00043 and фmax = 0.062. Uncertainties
about έ, proportionality, and respiration made
these values less valuable. The assemblage of
curves presented by MOREL (1978)
showed proportionality, estimated value of
фmax.έ = 0.0005. However, MOREL did not
of TAKEMATSU et al (l98l) did nor demonstrate parallelism between InpB and 1 nI. only
three points were within the light-limited
range. A straight line fitted to these three points
produced a slope, фmax.έ of 0.0004 - 0.0005
and estimated фmax were 0.04 - 0.05.
PLATT and JASSBY (1976) presented data
in which proportionality was very well shown.
Although
they
made
some
wrong
assumptions, their data could still be used to
calculate corrected values of фmax.έ and фmax.
Mean values of фmax.έ and фmax. over a year
were 0.0010 and 0.05 -0.10 respectively.
WELSCHMEYER and LORENZEN (1981)
carried out a careful determination of α
(фmax.έ) and фmax. They measured separately
the two functions of six algae in exponential
cultures under light-limited conditions.
Similar measurement was also made for a
single diatom species through its growth
cycle in culture. фmax was estimated from
irradiance, absorption, and carbon uptake all
measured in an integrating sphere illuminated
with tungsten lamp. And фmax.έ was estimated
from the slope of light curves measured
independently for the same cultures under
fluorescent lamp. Their results were sum-
make any conclusion about έ that can be applied to
his data, thus фmax cannot be calculated. Results
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marized by BANNISTER and WEIDEMANN
(1984) and are shown in Table l. For these
data, BANNISTER and WEIDEMANN also
calculated the values of έ which should be
correct provided фmax was the same for both
fluoresent and fungsten illumination, and
carbon uptake in the sphere was corrected for
respiration.
WELSCHMEYER
and
LORENZEN
(1981)
also
produced
evidence that фmax was statistically constant
among the six species of marine
phytoplankton. In contrast, фmax.έ was
statistically different for these six species. This
implies that έ is highly variable.
the size and shape of phytoplankton cells. έ
also depends on the ratio of all photosynthetic
pigments to chlorophyll (DUBISNKY and
BERMAN, 1979), and on changes in physiological state and cellular chlorophyll levels
(FALKOWSKI, 1984).
From earlier estimates, BANNISTER
(1979) suggested that the value of έ might be
roughly 0.016. Subsequently, MOREL (1978)
and ATLAS and BANNISTER (1980) found
that έ was close to 0.014 for several algal types
in light at the surface, but could vary between
0.005 and 0.025 at depth depending on water
colour and algal type. Values of more than 0.03
could conceivably occur in blue water with
algae containing large amounts of carotenoid
relative to chlorophyll. e.g. green algae.
Spectra of έ have been reported for
Chlorella (BANNISTER. 1979), Thalassiosira
REVIEW ON PIGMENT-SPECIFIC
LIGHT ATTENTUATION ( έ )
KIRK (1975 a, b) suggested on a theoretical ground that values of έ depend upon
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pseudonana and Pavlova lutheri (KEEPER et
al., 1979), and Platymonas suecica,
Cocolithus
huxleyi
and
Chaetoceros
protuberans (MOREL and BRICAUD,
1981). PRIEUR and SATYENDRANATH
(1981) derived a spectrum of relative values of
ε ( λ) for marine phytoplankton. In all of these
spectra, values of ε at 675 nm range narrowly
between 0.02-0.03. DUBINSKY
and
BERMAN (1979) recommended that
measurements of ε are made at the red
spectral region (650 nm) because the
absorption of chlorophyll is relatively free from
carotenoids interferences. Table 2 presents a
list of ε values from different sources.
The best estimates of mean specific attenuation coefficient are usually derived from
spectral e and spectral irradiance, calculated
by the following equation (ATLAS and
BANNISTER, 1980; BANNISTER and
WEIDEMANN, 1984).
Method applicable for laboratorygrown phytoplankton is the measurement of
absorption spectrum with an Ulbricht integrating sphere (LATIMER and RABINOWITCH,
1959; KIEFER et al. 1979; KIRK, 1980) or
an opal glass cuvette (SHIBATA, 1958; BANNISTER, 1979; MOREL and BRICAUD,
1981). Both techniques avoid multiple scattering and seem to give the same spectrum, because algae mainly scatter in the forward direction (particle scattering).
Regression analysis of the vertical attenuation coefficient Kd (m -1 ) versus
chlorophyll concentrations for estimating e, first
introduced by TALLING (1960), has been
widely applied (e.g. GANF, 1974; TYLER,
1975; BINDLOSS, 1976; SMITH and
BAKER, 1978; MEGARD et al, 1979;
TILZER, 1983,1984).
MOREL and PRIEUR (1977)
employed a distinct method in order to estimate
έ. From pairs of station which have about the
same sacttering coefficient (=b) but different
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chlorophyll concentration, they were able to
estimate e by subtracting spectral e curve of
one station from that of the other station.
DUBINSKY et al (1984) described a
method for in situ determination of e. Increasing concentrations of chlorophyll retained on
filters were held under a holder clamped on to
an underwater irradiance sensor. Light profiles,
then, were measured with each fiter. The e for
each depth was estimated from a fitted line to
an exponential regression of irradiance versus
areal concentration of chlorophyll retained on
the filters. By employing this method, they
determined a range of e from 0.0166 at the
surface to 0.0118 at 15 m depth in Lake
Constance.
FAKOWSKI, P.G. 1984. In : RILEY, J.P. and
G. SKIRROW (eds), Chemical Oceanography, Vol. 2, London, Academic
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GOVINDJEE, R.; E. RABINOWITHCH and
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JEWSON, D.H.; J.F. TALLING; M J. DRING;
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KIEFER, K.; R J. OLSEN and W.H. WISON.
1979. Limnol Oceanogr. 24 : 664.
KIRK, J.T.0.1975. New Phytol 75 : 11.
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