Laval, F-72017 Le Mans Cedex, France (* author for correspondence); 2Laboratoire de Biologie marine fondamentale .... filtration, sea water was left to rest 24 h before use, so that the ..... Dalev D, Danchev D, Lidhzi L (1957) The dynamics of.
Journalof Applied Phycology 2: 281-287, 1990. © 1990 Kluwer Academic Publishers. Printed in Belgium.
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Effects of environmental parameters on net photosynthesis of a free-living brown seaweed, Cystoseira barbata forma repens: determination of optimal photosynthetic culture conditions D. Baghdadli 1 3, G. Tremblin ',* M. Pellegrini 2 & A. Coudret3 lLaboratoire de Biologie et Physiologie Vigetales, Faculte des Sciences, UniversitJ du Maine, route de Laval, F-72017 Le Mans Cedex, France (* authorfor correspondence); 2 Laboratoirede Biologie marine fondamentale et applique, Facultg des Sciences de Luminy (Case 901), 163 Avenue de Luminy, F-13288 Marseille Cedex 09, France;3 Laboratoirede Physiologie Vgdtale, UniversitJde Clermont II, 4, rue Ledru, F-63000 Clermont-Ferrand,France Received 7 March 1990; revised 26 July 1990, accepted 30 July 1990
Key words: Cystoseira barbata, photosynthesis, light, temperature, salinity
Abstract The net photosynthesis of the Mediterranean brown seaweed Cystoseira barbataf. repens is measured according to irradiance, temperature and salinity. There is not only, a good utilization of low light intensities (light-shade adaptation), but also a specific ability to use a broad range of irradiance, which corresponds in the photosynthesis-irradiance curves to a high initial slope and an extended light saturation level from 300 to 1500 /mol photon m-2 s - '; only very high irradiances induce photoinhibition. Maximum net photosynthesis occurred at temperatures ranging from 20 C to 30 OC. The alga tolerates not only a low level of salinity, but also a slight increase in salinity; however, at more than 47.5 g 1 - NaCl, oxygen exchange is significantly reduced. Light, temperature and salinity requirements are discussed, taking into account ecological considerations. Yields and quality of alginic acid are presented according to the irradiance and yearly evolution in situ in order to aid future cultivation of this species.
Introduction When considering the diversity of recent industrial applications of phycolloids, and the practical limits for harvesting and cultivating along the French Mediterranean coast, culture away from the sea appears to be a likely future solution. The economic value of any such culture is, however, closely linked to a judicious choice of alga and to
a detailed knowledge of the physiology of the species selected. Among the brown seaweeds, the genus Cystoseira, abundantly represented in the Mediterranean, may provide an original and interesting subject, in so far as the phytochemical chaiacteristics of several species of this genus have been studied recently (Pellegrini, 1971; Pellegrini & Pellegrini, 1971 a, 1971 b, 1972; Gilven & Bergisadi, 1973; Glombitza et al., 1975; Gtlven
Correspondence address: G. Tremblin, Laboratoire de Biologie et Physiologie vegetales, Facult6 des Sciences, Universit6 du Maine, route de Laval, F-72017 Le Mans Cedex, France.
282 et al., 1976, 1980; Gombault et al., 1976; Banaigs et al., 1982; Amigo et al., 1984). In C. barbata a number of economically interesting compounds were isolated and quantified. Yatsenko (in Guven et al., 1976), noted, for example, the variable (but often elevated) quantity of alginic acid (38-44 %); while P. Doumenq (pers. comm.) noted 17-44% in the fixed form C. barbataf. hoppi, and a little less than 16 % in the free form C. barbataf. repens. But this free-living form multiplies itself in-situ principally by self-propagation, which facilitates its use in experimental and industrial cultivation. The first tests already carried out confirm these abilities (P. Doumenq, pers. comm.). However, any such exploitation requires a detailed knowledge of the ecophysiological characteristics of this species; especially of its photosynthetic reactions according to the various environmental factors, in order to optimize its culture conditions. Previous work on fixed and surface forms of Cystoseira, has shown in some cases, the absence of photosynthetic inhibition, even with very high irradiance, e.g. C. elegans Sauv. (Coudret & Jupin, 1985). Moreover, these algae show very specific variations of their photosynthetic activity under the influence of environmental factors; with C. stricta (Mont.) Sauv. and C. crinita (Desf.) Bory the photosynthetic reactions may well be linked to the natural conditions of their implantation and preferential installation (Tremblin et al., 1986). In view of this, the action of three abiotic factors easily modifiable in cultures - light, temperature and salinity - has been studied in a species of medium deep-sea Cystoseira (C. barbata f. repens) in order to define the optimal photosynthetic conditions for its development.
Materials and methods Alga harvesting and Culture Cystoseira barbata f. repens, is a Mediterranean fucoid recently observed in the Thau basin (Pellegrini etal., 1985), where it abounds on a sandy-silty bottom in depths ranging from 1 to
3 m of water. This free-living form of C. barbata usually prefers sites where hydrodynamic effects are minimal, but is has recently been rediscovered in wave-influenced and less deep sites in other lagoon formations on the Mediterranean coast (unpublished data). In this study, after harvesting by divers in the 'Eaux blanches' basin (Bassin de Thau), the thallus was cleaned carefully, kept in aquaria filled with sea water (natural or synthetic), continuously aerated (air pump) and frequently renewed to minimize possible limiting effect of CO 2 or nutrients. Before measurements, the algae were maintained for a few days under low light supply to minimize any possible effects due to daily endogenous or exogenous photosynthetic periodicity in a thermoregulated chamber (15 C + 1 C); light was provided by cool-white fluorescent tubes on a 14:10 lighttodarkcycleunder60 imolphoton m-
2
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1 (PAR) irradiance.
Experimental methods Samples of thallus (1.3 to 1.5 g) including primary, secondary and tertiary axes were taken from growing tips, as often as possible two hours after the beginning of the irradiance period, and put in a cylindrical measurement glass chamber (140 ml) entirely filled with filtered sea water (after filtration, sea water was left to rest 24 h before use, so that the initial 02 concentration was near 75 % saturation before measurement); it was verified that, during the short measurement period used (< 15 min), no 02 supersaturation occurs in the glass chamber (final 02 concentration always below 95 % saturation). Lighting was provided by a 1000 w quartz-halogen lamp capable of providing an irradiance of up to 2000 ,umol photon m - 2 s-'. As it was not possible to monitor irradiance inside the measurement chamber, the value for photosynthetically active radiation (PAR 400-700 nm) was measured continuously using a quantum meter sensor inside the centre of a similar chamber (allowing for absorption by water and glass), put near the 02 measurement
283 chamber at an equal distance from the light source; this measurement is an approximation (+5%) for the light intensity actually incident upon the surface of these finely branched thalliforms, but as thalli are free-living in sea water continuously stirred during measurement, no selfshading existed in the measuring cell and photon flux measured is an acceptable evaluation of irradiance received by the alga. Photon flux density was varied by adjusting the distance between measuring cell and light source accordingly. During the measurement, the temperature was maintained by circulating water from a constant temperature bath through the water jacket of the glass chamber. The oxygen sensor inserted in the lid was connected to a Shott Gerate oxymeter and permitted a continuous recording of the variation in oxygen concentration. The analogue signals are digitalised and recorded in a computer (Apple IIe) and, in real time, a regression linear program was used to select the available linear part of the appropriate data. The slope of the curve selected was then calculated and the photosynthetic rate quickly and directly determined and recorded in relation to the incident light-intensity, according to the experimental method previously described (Tremblin et al., 1986; Tremblin et al., 1987). As the effects of 02 concentration on algal photo-
synthesis and respiration are well known, all the calculations were made in the range 75-85 % dissolved 02. In each case, the measurement of photo2 h-lg - l d.wt.) was synthetic rate (mol repeated at least 6 times (6 separate thalli for P/I curve and 2 measurements on 3 separate thalli in other experiments). Respiration was measured under similar conditions after darkening the glass chamber. All the samples could not be taken at the same time, so the photosynthesis-irradiance (P: I) curve plotted is the mean of a family of P: I curves; equation and descriptive parameters were estimated by fitting the data to several functions previously used by Gattuso and Jaubert (1985). When the study temperature and salinity parameters, or when the photosynthesis rate evolution is studied during a daily cycle, a constant light intensity saturating the photosynthesis in culture conditions (15 ° C or 37.5%0 salinity) is used. Thus, it has been verified (Fig. 1) that no significant variations of photosynthetic activity exist during the day (Fisher's F-test: p < 0.05) However, diel oscillations of photosynthesis are frequently observed in macro-algae in situ (Ramus & Rosenberg, 1980; Gattuso & Jaubert, 1985) and in laboratory culture conditions (Kagemaya et al. 1979; Levavasseur & Giraud,
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Fig. 1. Daily evolution of photosynthetic intensity (in % of the maximal photosynthetic intensity measured) in cystoseira barbata f. repens (T = 15 °C, irradiance= 850pmol photon m-2s-'). Mean +S.E. (n=6); absolute photosynthetic rate = 100.4 + 4.2 /mol 02 h- ' g- ' d.wt.
284 1982). The lack of daylight photosynthesis variations, is probably due to the culture conditions of the thallus (low and constant light intensity and constant temperature during daylight), according to Oochusa (1980). Thus our samples could be taken a random times during the daylight cycle.
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s ,, 50
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TEMPERATURE(C)
Fig. 3. Photosynthetic responses for Cystoseira barbata f. repens to temperature; mean + S.E. (n = 6).
Results Photosynthesis and light intensity Photosynthesis-irradiance measurements were conducted at 15 C (temperature of sea water in the culture chamber), and the most significant P: I curve (Fig. 2) was plotted. (The best results are given by the exponential, but only the values of oxygen exchange obtained prior to the maximum irradiance were used for fitting data: Gattuso & Jaubert, 1984.) The curve obtained shows a very rapid increase in oxygen release under low-light intensity (between 0 and 300 ,mol photon m- 2 s- ), with stabilization afterwards (light saturation level), at an average value of 114.3 + 4.3 pmol 02 h- g-' d.w.t. (net maxi-
mum photosynthetic rate = Pmax). The plateau of saturating irradiance goes from 300 to 1500 pmol photon m - 2s-. Beyond this value, photoinhibition appears, but the net photosynthesis is only reduced significantly (about 30% of Pm,,) by a high irradiance level (over 1700 pmol photon m-2s- ).
Temperature and salinity Figure 3 shows the variations of net photosynthesis in relation to temperature under lightsaturating conditions. The 02 release is maximal at 25 C; however, a 5 C change near this optimum does not significantly modify the photosynthetic rate (P < 0.05); on the other hand, it is reduced by 50% at 15 C and decreases rapidly above 35 C. At a lower temperature (10 °C) the
I 1. a
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100 S
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IRRADIANCE
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50
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(Irml m'r ')
Fig. 2. Most significant Photosynthesis-irradiance curve with + S.E. (n = 6) for Cystoseira barbata f. repens: - Solid line: result of curve fitting to an saturated exponential function Y = A(1-e-
K(X-B)),
with Y
.
Ir,
17n.
27.,
37.1
47.5
_I I 57.5
67.,
SALINITY (gl' )
oxygen exchanges
prior to the maximum irradiance; X = irradiance; K = constant (=0.0157); A = maximum net photosynthetic rate (= 114.2); B = compensation irradiance (= 11.9). - Dotted line: photoinhibition curve plotted by hand.
Fig. 4. Photosynthetic responses (% of maximal net photosynthesis) for Cystoseira barbata f. repens to salinity; mean + S.E. (n = 6). Absolute photosynthetic rate = 99.9 + 8.1 #mol 0 2 h- ' g- ' d.wt.
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photosynthetic rate is only a third of the optimal value. With the two lowest salt levels used (17.5 and 27.5%0) in saturating light (Fig. 4), the alga shows the same photosynthetic response as that measured in natural sea water (37.5%o). However, a slight increase in salinity (47.5%0) enhances the net photosynthetic rate, when it is 20% higher than the reference point (in natural sea water); above this salinity level (57.5 and 67.5%), the photosynthetic performance is strongly reduced (about 40 %).
Discussion Cystoseira barbata f. repens, a species living at medium depth, shows photosynthetic characteristics very different from the surface species previously studied (Coudret & Jupin, 1985; Tremblin et al., 1986) for which the photosynthesis does not seem to be saturated by the high irradiance level used. In C. barbatathe absolute photosynthetic rate (Pm = 114.3) appears to be much lower than rates previously measured for C. stricta, C. crinita and C. elegans. This might suggest that C. barbatais not a very productive species, at least under high irradiance level. However the P: I curves obtained show a higher mean = 2.85 + 0.24 pmol O2 value of initial slope: h- g- ' d.w.t. (mol photon m - 2 s- )- l, signi-
ficantly higher than initial slope obtained for other species previously studied (Tremblin et al., 1986); thus, at low irradiance (
