Biomass, photosynthesis and growth of Laminaria saccharina in a high-arctic fjord, NE Greenland

Biomass, photosynthesis and growth of the large, perennial brown alga Laminaria saccharina (L.) Lamour. were examined along a depth gradient in a high-arctic fjord, Young Sound, NE Greenland (74°18'N; 20°14'W), in order to evaluate how well the species is adapted to the extreme climatic conditions. The area is covered by up to 1.6-m-thick ice during 10 months of the year, and bottom water temperature is <0°C all year round. L. saccharina occurred from 2.5 m depth to a lower depth limit of about 20 m receiving 0.7% of surface irradiance. Specimen density and biomass were low, likely, because of heavy ice scouring in shallow water and intensive feeding activity from walruses in deeper areas. The largest specimens were >4 m long and older than 4 years. In contrast to temperate stands of L. saccharina, old leaf blades (2-3 years old) remained attached to the new blades. The old tissues maintained their photosynthetic capacity thereby contributing importantly to algal carbon balance. The photosynthetic characteristics of new tissues reflected a high capacity for adaptation to different light regimes. At low light under ice, or in deep water, the chlorophyll a content and photosynthetic efficiency (!) were high, while light compensation (E_c) and saturation (E_k) points were low. An E_c of 2.0 µmol photons m^-2 s^-1 under ice allowed photosynthesis to almost balance, and sometimes exceed, respiratory costs during the period with thick ice cover but high surface irradiance, from April through July. Rates of respiration were lower than usually found for macroalgae. Annual elongation rates of leaf blades (70-90 cm) were only slightly lower than for temperate L. saccharina, but specific growth rates (0.48-0.58 year^-1) were substantially lower, because the old blades remained attached. L. saccharina comprised between 5% and 10% of total macroalgal biomass in the area, and the annual contribution to primary production was only between 0.1 and 1.6 g C m^-2 year^-1.     

Ecotypic differentiation in light-related traits of the kelp Laminaria saccharina

Light-related traits were compared for Laminaria saccharina Lamour. collected from three habitats in Maine and New York, USA, with different ambient light regimes. Light-level, expressed as a proportion of surface irradiance (I₀), ranged from 0.04 to 0.32 I₀ in the shallow habitat, but rarely exceeded 0.04 I₀ in the deep and turbid habitats. Juvenile sporophytes collected from each habitat in April, 1985, were grown at four acclimation light-levels (0.065, 0.12, 0.26, and 0.54 I₀) in a common-garden, laboratory experiment. Photosynthesis vs irradiance (PI) parameters, light-harvesting characteristics, and rates of carbon-assimilation and growth were determined for each group of plants. The results indicated that ecotypic differentiation had occurred among the three kelp populations. Photosynthetic capacity (P_max) and photosynthetic efficiency () were generally highest for plants from the turbid habitat, lowest for deep plants, and intermediate for shallow plants. These differences were largely attributable to variations in light-harvesting characteristics. The nature and magnitude of photoacclimation responses also differed among populations. Population differences in photosynthetic parameters resulted in different rates of C-assimilation and growth by plants from shallow, deep, and turbid habitats. Predictions of in situ growth rates indicated that the severity of light-limitation and, therefore, the adaptive significance of efficient light-utilization vary among the three populations. It is concluded that ecotypic differentiation in light-related traits is important to the broad environmetal range of L. saccharina.     

“Free space-photosynthesis” in the algae Fucus virsoides and Laminaria saccharina

This paper deals with the role of bicarbonates in the apparent free space (AFS) and their importance for the photosynthetic process. Both the littoral alga Fucus virsoides (Mediterranean Sea) and the sublittoral alga Laminaria saccharina (Baltic Sea) show the same response. Unloading of Clions and subsequent reloading of HCO₃-ions result in a positive photosynthetic rate in distilled water (free of CO₂). Time of exposure of an algal thallus to bicarbonate solutions, as well as the concentration of these solutions, influences AFS-assimilation of the ions.     

Temperature acclimation of respiration and photosynthesis in the brown algaLaminaria saccharina

Sporophytes of the brown algaLaminaria saccharina (L.) Lamour grown at 15°C contained significantly more chlorophylla (chla) than did similar plants grown at 5°C. The increase in chla in 15°C plants was due to increased numbers of photosystem II reaction centes, and possibly to increased photosynthetic unit size, compared with 5°C plants. These changes were associated with increased values (photosynthetic efficiencies) in 15°C-grownL. saccharina relative to 5°C-grown plants. The changes in together with reduced respiration rates allowed 15°C-grownL. saccharina to achieve net photosynthesis and light-saturated photosynthesis at a lower photon fluence rate (PFR) than 5°C plants when both groups were assayed at the same temperature (15°C). The photon fluence rates necessary to reach the compensation point and achieve light-saturated photosynthesis (I _c andI _k , respectively) increased with increasing incubation temperature inL. saccharina grown at both 5 and 15°C. However, acclimation responses to growth temperature compensated for the short-term effect of temperature onI _c andI _k . Consequently, plants grown at 5 and 15°C were able to achieve similar rates of light-limited photosynthesis, and similarI _c andI _k values at their respective growth temperatures. These responses are undoubtedly important for perennial seaweeds such asL. saccharina, which frequently grow in light-limited habitats and experience pronounced seasonal changes in water temperature.Please address all correspondence and requests for reprints to I.R. Davison     

Photoinhibition and recovery of the kelp Laminaria saccharina at optimal and superoptimal temperatures

Effects of high irradiance on photosynthetic characteristics were examined in sporophytes of the kelp Laminaria saccharina Lamour. from 1992 to 1994. Exposure to high irradiance (700 mol photons m^-2s^-1) for 1 h at optimal temperature (12°C) caused a 40 to 60% decline in photosynthetic efficiency (alpha), quantum yield, and the ratio of variable to maximum chlorophyll fluorescence (F_v/F_m), an indicator of Photosystem II efficiency. Although the photoinhibition effects were partly attributable to protective mechanisms, a concurrent increase in minimal fluorescence (F_o) indicated damage to Photosystem II reaction centers. The magnitude of photoinhibition was proportional to irradiance and duration; however, F_v/F_m was significantly reduced after exposure to irradiances as low as 40 to 50 mol photons m^-2s^-1 for 1 h, or to 700 mol photons m^-2s^-1 for only 5 min. In contrast, photosynthetic capacity (P_max) was affected only at much higher irradiance. Superoptimal temperatures up to 24°C did not exacerbate high-light effects. At 25°C, however, alpha and P_max were more susceptible to photoinhibition than at lower temperatures. Recovery from photoinhibition was examined by following F_v/F_m and F_o for 24 h after exposure to high light. Recovery of F_v/F_m was fastest during the first 1 to 3 h, and slowed or ceased after 6 to 12 h, while recovery of F_o was relatively constant over 12 h. Dithiothreitol, which blocks formation of energy-dissipating xanthophylls, reduced both the initial rate and extent of recovery. Chloramphenicol, which blocks chloroplast-encoded protein synthesis, had little effect on initial rates of recovery, but stopped recovery after 3 h. Thus, L. saccharina appears to rely on the xanthophyll cycle to protect the photosynthetic apparatus, and reversal of this protective mechanism causes the rapid initial recovery in F_v/F_m. Longterm recovery depends on repair of damaged reaction centers. Both the rate and extent of recovery were temperature-dependent. The initial rate was higher at 18 to 22°C than at 12°C, but the extent of recovery over 24 h declined with increasing temperature. High temperatures, therefore, appear to enhance protective mechanisms, but disrupt repair processes. L. saccharina from Long Island Sound, an ecotype adapted to low light and high temperature, showed slightly but consistently greater effects of photoinhibition than plants from the Atlantic coast of Maine, but exhibited faster recovery at superoptimal temperatures.     

Effect of growth factors and light quality on the growth,pigmentation and photosynthesis of two diatoms,Thalassiosira gravida and Phaeodactylum tricornutum

Recruitment, life span and growth rate were investigated in field and experimental populations of Abra alba (Wood) in Kiel Bay, FRG (55°N) from 1975 to 1978 to determine production to biomass (P:B) ratios and to assess the importance of A. alba to production by commercial fish. Life span and growth rates were determined from changes in length frequency modes at each site and from winter rings on the shell. A peak of recruitment usually occurred in August, sometimes followed by a second peak between December and February. Life span was between a little more than one year and two and a half years. Growth rates were highest at the two sites in offshore fishing grounds, where bivalves reached a mean length of 13 to 16 mm at the end of two years. At the inshore control site and in the nearby experimental containers, individuals reached a mean length of 7 mm at the end of two years. Production estimates ranged from 110 to 3.000 mg C m^-2 year^-1, differing markedly among sites and among years. Production was highest during the first year after recruitment, occurring mainly between July and December. Mortality occurred mainly between January and June, and was in approximate balance with production over a three-year period. Annual P:B ratios were from 1.3 to 3.4; a long-term mean P:B ratio of 2.2 is suggested for Kiel Bay populations of A. alba. Annual production by A. alba appears to exceed considerably consumption by fish of commercial size. The significance of A. alba in the food web of Kiel Bay may thus be as food for juvenile fish or for intermediate-level predators that are themselves prey for larger fish.Publication No. 431 of the Sonderforschungsbereich 95 Meer-MeeresbodenPublication No. 1031 of the CSIRO Marine Laboratories     

CO2 fixation and translocation in benthic marine algae. III. Rates and ecological significance of translocation in Laminaria hyperborea and L. saccharina

Translocation of ¹⁴C-labelled assimilates in Laminaria hyperborea and L. saccharina is strictly basipetal within the thallus. The lowermost 20 cm of the frond accumulates 71% (L. hyperborea) or 63% (L. saccharina) of the basipetallymoving translocate after a period of 96 h from initial feeding with NaH¹⁴CO₃. Whereas translocation was found to occur at all seasons in L. saccharina, which grows throughout the year, no translocation of newly synthesized photosynthate occurred in L. hyperborea in October, when no frond enlargement takes place, nor in January, when the new fond occurs as a tiny outgrowth. In L. hyperborea, organic material, assimilated by the old frond during the period of rapid growth, is exported at the rate of 0.5 mg C · dm^-2 · h^-1. In L. saccharina, 14 to 18 cm frond length are necessary for an elongation rate of the growing zone, situated in lowermost 10 cm of the frond, of 1 cm per week. The significance of translocation in the two Laminaria species is demonstrated by comparison of export rates with growth rates measured in situ and in the laboratory.Dedicated to Professor Dr. Otto Stocker on his 85th birthday.     

Reproduction,growth and mortality of the holothurian Cucumaria pseudocurata

Certain phases of the ecology of a sea cucumber (Cucumaria pseudocurata Deichmann, 1938) population at Shell Beach, Sonoma County, California (USA), were investigated. The sea cucumber is a brooder, lays large (1 mm diameter) yolky eggs, which undergo direct development. It forms large aggregations in the rocky intertidal zone, extending from the lower boundary of the Mytilus californianus beds to about zero tide-level. The gonad cycle was followed from September, 1970 to January, 1972. Spawning occurred in January, 1971 and January, 1972. The holothurians produce from 1 to as many as 340 eggs, depending on the size of the individual; they completely spawn-out in a few days. Hatching takes place about 1 month after egg laying. The main sources of mortality are predation by the sea star Pycnopodia helianthoides and wave action. Survival of the young is negatively correlated with density of the aggregation. C. pseudocurata increases in weight 10 to 30 fold in the first year, but much more slowly in later years. Individuals live perhaps 5 years or more, and do not become reproductive until about the third year. Dispersal is accomplished by the young being washed away to a suitable new habitat. The upper range of the intertidal distribution is determined by exposure to air, and the lower range by P. helianthoides predation.Contribution No. 1 of the Bodega Marine Sciences Association.     

Effects of high-frequency light fluctuations on growth and photoacclimation of the red algaChondrus crispus

High-frequency fluctuations due to wavefocusing are prominent characteristics of light in shallow marine environments. Effects of high-frequency (0.01 to 1 Hz) fluctuating light on growth rates of the red algaChondrus crispus Stackh., collected from Crane Neck Point, New York, USA, during July 1988, were determined by comparing plants grown under fluctuating and constant light regimes with similar daily irradiances. At high daily irradiance, growth rates were higher under fluctuating light than under constant light. Fluctuating light effects were frequency-dependent; growth was enhanced by fluctuations at 0.1 and 1 Hz, but not by fluctuations at 0.01 Hz. At low daily irradiance, growth rates were not affected by fluctuating light at any frequency tested. Enhancement of growth was not due to effects of high-frequency light fluctuations on photoacclimation responses ofC. crispus. Plants grown under fluctuating light at high daily irradiance actually exhibited lower photosynthetic capacity and efficiency (determined under constant light) than plants grown under constant light. These differences were attributable to variation in the density of Photosystem II reaction centers, which was low in plants grown under fluctuating light. Maximum turnover rate of whole-chain electron transport and activity of ribulose-1,5-bisphosphate carboxylase were affected by total daily irradiance, but not by high-frequency light fluctuations. Enhancement of growth under fluctuating light was partly attributable to reduced rates of dark respiration compared to rates of plants grown under constant light. The results also provided indirect evidence that high-frequency light fluctuations may enhance instantaneous photosynthetic rates. This effect could increase daily carbon gain and, therefore, stimulate growth ofC. crispus under high-frequency light fluctuations.     

Light absorption,photosynthesis and growth of Nannochloris atomus in nutrient-saturated cultures

Nannochloris atomus was maintained in exponential growth at photon flux densities (PFD) from 400 to 700 nm, ranging from 10 to 200 mol m^-2 s^-1. Growth was lightsaturated at PFDs in excess of 100 mol m^-2 s^-1, with a mean light-saturated growth rate at 23 °C of 1.5×10^-5s^-1 (1.2 d^-1). The light-limited growth rates extrapolated to a compensation PFD for growth that was not significantly different from zero, although no changes in cell numbers were observed in a single culture incubated at a PFD of 1.0 mol m^-2s^-1. Dark-respiration rates were independent of PFD, averaging 1.7×10^-6 mol O₂ mol^-1 C s^-1 (0.14 mol O₂ mol^-1 C d^-1). The maximum photon (quantum) efficiency of photosynthesis was also independent of PFD, with a mean value of 0.12 mol O₂ mol^-1 photon. The chlorophyll a-specific light absorption cross-section ranged from 3 to 6×10^-3 m² mg^-1 chl a and was lowest at low PFDs due to intracellular self-shading of pigments associated with high cell-chlorophyll a contents. The C:chl a ratio increased from 10 to 40 mg C mg^-1 chl a between PFDs of 14 and 200 mol m^-2 s^-1. These new observations for N. atomus are compared with our previous observations for the diatom Phaeodactylum tricornutum in terms of an energy budget for microalgal growth.     

Response of gametophytes of Ecklonia radiata (Laminariales) to temperature in saturating light

Gametophytes of Ecklonia radiata (C.Ag.)J.Ag. from two New Zealand locations with different field temperature ranges were exposed to temperatures of 5° to 26°C in saturating light. Plants from Goat Island Bay (Lat. 36° 16S, Long. 174°48E) grew in 9.3° to 25°C and reproduced in 9.3° to 24°C. There was no growth at 8°C and plants died at 26°C. Plants from the cooler location, Houghton Bay (Lat. 41°20S, Long. 174°40E), grew from 8° to 24°C and reproduced up to 15°C but not at 21.5°C. The plants did not grow at 6°C and died at 26°C. The timing of the first cell division and subsequent growth rate were retarded close to the upper and lower tolerance limits. Reproduction was a broad optimum of roughly 12° to 20°C. Within this range, fertile female gametophytes grown at lower temperatures had fewer, larger cells and thus fewer potential ova than those grown at higher temperatures.     

High-temperature tolerance of photosynthesis in the red alga Chondrus crispus

Chondrus crispus (Stackhouse) is a perennial red seaweed, common in intertidal and shallow sublittoral communities throughout the North Atlantic Ocean. In the intertidal zone, C. crispus may experience rapid temperature changes of 10 to 20C° during a single immerison-emerision cycle, and may be exposed to temperatures that exceed the thermal limits for long-term survival. C. crispus collected year-round at Long Cove Point, Chamberlain, Maine, USA, during 1989 and 1990, underwent phenotypic acclimation to growth temperature in the laboratory. This phenotypic acclimation enhanced its ability to withstand brief exposure to extreme temperature. Plants grown at summer seawater temperature (20°C) were able to maintain constant rates of lightsaturated photosynthesis at 30°C for 9 h. In contrast, light-saturated photosynthetic rates of plants grown at winter seawater temperature (5°C) declined rapidly following exposure to 30°C, reached 20 to 25% of initial values within 10 min, and then remained constant at this level for 9 h. The degree of inhibition of photosynthesis at 30°C was also dependent upon light intensity. Inhibition was greatest in plants exposed to 30°C in darkness or high light (600 mol photons m^-2s^-1) than in plants maintained under moderate light levels (70 to 100 mol photons m^-2s^-1). Photosynthesis of 20°C-acclimated plants was inhibited by exposure to 30°C in darkness or high light, but the degree of inhibition was less than that exhibited by 5°C-grown plants. Not only was light-saturated photosynthesis of 20°C plants less severely inhibited by exposure to 30°C than that of 5°C plants, but the former also recovered faster when they were returned to growth conditions. The mechanistic basis of this acclimation to growth temperature is not clear. Our results indicate that there were no differences between 5 and 20°C-grown plants in the thermal stability of respiration, electron transport associated with Photosystems I or II, Rubisco or energy transfer between the phycobilisomes and Photosystem II. Overall, our results suggest that phenotypic acclimation to seawater temperature allows plants to tolerate higher temperatures, and may play an important role in the success of C. crispus in the intertidal environment.     

Light and temperature demands for growth and reproduction of laminarian gametophytes in southern and central California

The gametophytes of 9 laminarian species (4 from southern California, and 5 from central California, USA) became fertile in the unicellular stage (female gametophytes) or in a few-celled stage (male gametophytes), when appropriate temperatures and a sufficiently high quantum irradiance in the blue part of the spectrum were supplied. Vegetative growth, leading to the formation of filamentous gametophytes was light-saturated at relatively low irradiances (4 W m^-2; equivalent to about 2 nE cm^-2 sec^-1 or an illuminance of 1000 lux), whereas 2 to 3 times this irradiance in continuous fluorescent cool white light was needed to induce the majority of the gametophytes to become fertile. An illuminance of 8300 lux did not inhibit the development of the gametophytes from southern Californian species. Egregia menziesii exhibited an exceptionally low quantum demand for induction of fertility. Gametophytes of species from central and southern California differed in regard to their temperature optimum for growth (12°C in the former, 17°C in the latter) and their upper temperature limit for reproduction (17°C in the former, 20°C in the latter).     

Reproduction and development of the blue coralHeliopora coerulea (Alcyonaria: Coenothecalia)

Up to the present time, the reproductive cycle and larval development ofHeliopora coerulea, living fossil and sole member of the alcyonarian order Coenothecalia, have been undescribed. Populations ofH. coerulea studied on the Great Barrier Reef between 1984 and 1989 were found to have separate sexes and an annual gametogenic cycle. Mature eggs were large (>800µm diam), and their development was initiated internally. There appeared to be a lunar or semi-lunar periodicity in reproductive behaviour, with brooding of larvae commencing around either full or new moon. Development proceeded via superficial cleavage and a solid stereoblastula. Subsequent development took place on the surface of the colony, within a temporary brood-space created by protracted distension of the polyps. Larvae lacked zooxanthellae and were brooded for between 6 and 14 d prior to leaving the colony. Reproduction and development reflected the taxonomic affinities ofH. coerulea, but brooding and embryological development also appeared to be constrained by its morphology. Reproductive and larval characteristics ofH. coerulea may offer a partial explanation of the current biogeographic range ofH. coerulea.     

Different patterns of carotenoid composition and photosynthesis acclimation in two tropical red algae

To be able to survive, marine macroalgae in shallow coastal waters need mechanisms for short-term acclimation to fast changes in their environment. Of major importance are mechanisms that regulate the efficiency of photosynthesis by protecting PS II from photo-oxidative damage. Carotenoids, xanthophyll cycles and non-photochemical quenching (NPQ) are central constituents of such protection mechanisms. Red algae as a group do not have a universal carotenoid composition. We screened ten red algal species and selected two species, originating from similar ecological conditions but with different carotenoid compositions, for use in irradiance-acclimation experiments. We selected the tropical intertidal species Gracilaria domingensis and Kappaphycus alvarezii with antheraxanthin and lutein as major xanthophylls, respectively. Simultaneous in vivo fluorescence and O₂ evolution experiments were performed at different irradiance levels, which allowed a direct comparison of overall photosynthetic performance with NPQ. Interconversions of xanthophylls (violaxanthin, zeaxanthin, β-cryptoxanthin and one unidentified carotenoid) did occur in G. domingensis, but not in response to sudden exposure to light. Thus, NPQ was not correlated with any xanthophyll cycle during short-term acclimation to light. G. domingensis had five times higher weight-specific photosynthetic rates than K. alvarezii, which can be explained by the thicker thallus of K. alvarezii. Chlorophyll-specific gross photosynthetic rates were higher in K. alvarezii, but net rates were the same for both species. G. domingensis showed an immediate strong onset of NPQ upon exposure to irradiance, followed by downregulation to the NPQ level required. In K. alvarezii NPQ increased slowly until the required NPQ level was reached. At high irradiance G. domingensis downregulated photosynthesis while K. alvarezii continued to produce O₂ even at 2,000 μmol photons m⁻² s⁻¹ without NPQ increase. The strategy of K. alvarezii may provide short-term gains but with the risk of oxidative damage. The fast onset of NPQ in G. domingensis even at subsaturating irradiance as well as downregulation of photosynthesis when NPQ is saturated might provide this species with a competitive advantage under conditions of changing irradiance in the field.     

有机氮比例和光强对赤潮藻球形棕囊藻生长和光合作用的影响

采用实验室一次性培养的方法,研究了有机氮比率和光照强度相互作用对赤潮藻球形棕囊藻（Phaeocystis globosa）生长和光合作用的影响。结果表明,在高光条件下（120μmol.m-2.s-1）,有机氮含量为20%时,其细胞密度、比生长率均显著高于对照组和其他处理组,球形棕囊藻生长最好;在低光条件下（10μmol.m-2.s-1）,有机氮含量大于50%时,其细胞密度要高于硝态氮和有机氮为20%的实验组。无论是高光还是低光条件下,有机氮含量变化对球形棕囊藻Fv/Fm影响不大。但在高光条件下,不同氮源对其Fv/Fm有显著的影响,硝氮组显著高于尿素组而在低光照条件下,以尿素为唯一氮源的对照组达到最大光能转化效率0.752,但与硝氮组差别不显著。对于既能利用无机氮又能利用有机氮的海洋微藻来说,有机氮的存在可能显著促进其增殖,从而改变浮游植物群落结构,并可能在适宜的环境条件下形成赤潮。     

Seasonal growth in Laminaria longicuris: Relations with reserve carbohydrate storage and production

Growth rates of Laminaria longicruris increase during January and February, and the role of carbohydrate reserves as a carbon source for this growth was investigated. Seasonal variations in the levels of laminaran and mannitol showed maximum values for both in late summer. Minimum values occurred in February at the time when growth rates were increasing rapidly. Erosion of the blades in winter carried away much of the tissue containing carbohydrate reserves accumulated during the previous summer. Experimental reduction of carbohydrate reserves by fertilization with sodium nitrate during the summer did not affect subsequent winter growth rates. Truncation of the plants in November significantly reduced growth rates. The lower rate of growth is attributed to a reduction in photosynthetic area rather than a loss of storage products.NRCC No. 16478     

Diurnal photosynthesis, water use efficiency and light use efficiency of wheat under Mediterranean field conditions

Photosynthesis and transpiration rates of wheat leaves (Triticum aestivum L.) were measured at 30 min intervals under Mediterranean field conditions, using Photosynthesis Monitor system (PM-48M). The dynamics of net photosynthetic rate (P(N)), transpiration rate (E(T)), water use efficiency (WUE), light use efficiency (LUE), stomatal conductance (g(s)), photosynthetically active radiation (PAR), air temperature (T), relative humidity (RH), and atmospheric CO2 concentration (Catm) were quantified at five rainfed wheat sites with the same stages of development (midflowering) along south-to-north and east-to-west transects for eight days in April. Diurnal P(N) (3.6 to 6.6 micromol m(-2) s(-1)), PAR (392 to 564 micromol m2 sec(-1)), LUE (0.006 to 0.015) and WUE (0.0001 to 0.011) did not vary significantly across all five wheat sites (p > 0.05). P(N) and E(T) were strongly coupled and highly correlated with PAR (p < 0.001). Best multiple linear regression (MLR) models accounted for 92% of variations in P(N) as a function of PAR and E(T), and 90% in E(T) as a function of PAR and RH (p < 0.001). P(N) exhibited a peak at mid-morning, and a photosynthetic midday depression under the limiting effects of high evaporative demand. Diurnal variations in WUE and LUE showed a bimodal behavior with the maximum values in early morning and late afternoon. As the impacts of global climate change become increasingly felt, continuous measurements of climate-crop-soil-managementinteractions under natural conditions play a pivotal role not only in exploring changes in ecophysiological properties of strategic crops for food security such as wheat but also in devising preventive and mitigative management practices to ensure sustained agricultural productivity.     

Optimal growth and maximal survival temperatures of Atlantic Laminaria species (Phaeophyta) in culture

The effects of temperature on growth rate of rapidly-growing cultured macrosporophytes of 9 isolates of Atlantic Laminaria comprising 4 species have been investigated. No significant population variation was observed within species despite wide variations in temperature between the original collecting sites. L. saccharina showed a broad temperature optimum in the 10°–15°C range, whereas L. longicruris had a sharp optimum at 10°C. L. digitata and L. hyperborea grew more slowly, with only slightly sub-optimal growth over a wide temperature range, but with peaks at 10°C (L. digitata) and 15°C (L. hyperborea). The maximum survival temperatures of individual male and female vegetatively-growing gametophytes were ascertained for these species plus the Arctic L. solidungula, and were as follows: L. saccharina and L. longicruris, 23°C; L. digitata (male), 23°C; L. digitata (female), 22°C; L. hyperborea, 21°C; L. solidungula, 18°C. The lack of within-species differences demonstrates that the success of the genus in areas with different temperature regimes is brought about by phenotypic plasticity of individuals rather than the selection of temperature races or ecotypes.