Nitrogen uptake characteristics of Chordaria flagelliformis (Phaeophyta) in batch mode and continuous mode experiments

The uptake of NH ₄ ⁺ and urea by Chordaria flagelliformis was measured in a perturbed system (batch mode) and in an apparent steady-state system (continuous mode). The maximum uptake rates (V_max) measured in short-term depletion experiments greatly exceeded those determined under a steady nutrient supply. C. flagelliformis briefly exposed to high nutrient concentrations has an impressive capacity for rapid uptake (high V_max)_which is uncoupled from growth. In contrast, under continous, homogenous low N concentrations the alga appears well equipped (low half-saturation constant, K_m) to take up the available N. The results show that previous work based on batch mode uptake experiments probably overestimated the N requirements for the growth of many seaweeds.     

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.     

The section Digitatae of the genus Laminaria (Phaeophyta) in the northern and southern Atlantic: crossing experiments and temperature responses

Hybridization experiments between seven north and south Atlantic Laminaria species were carried out. Morphologically normal F₁ sporophytes developed from the following crosses among south Atlantic species: L. pallida x L. schinzii, L. pallida x L. abyssalis and L. schinzii x L. abyssalis. Normal F₁ sporophytes also resulted from the crosses L. digitata (north Atlantic) x L. pallida (south Atlantic) and L. digitata (north Atlantic) x L. abyssalis (south Atlantic). Hybrids between north Atlantic L. ochroleuca and south Atlantic L. pallida, L. schinzii and L. abyssalis and between north Atlantic L. digitata and south Atlantic L. schinzii initially developed as normal sporophytes but became deformed later on and further development was retarded. No hybrids resulted from attempted crosses between northeastern Atlantic L. saccharina and L. abyssalis from Brazil. Temperature tolerance, relative growth rates and temperature demands for gametogenesis revealed the existence of a warm temperate group within the digitate Laminaria species consisting of L. ochroleuca, L. pallida, L. schinzii and L. abyssalis. Hybridization experiments and temperature responses suggest that north Atlantic L. digitata and L. ochroleuca are still similar to south Atlantic Laminaria species, confirming the speculation that a transequatorial migration of a warm-temperate L. ochroleuca-like ancestor may have taken place.     

Bioavailable iron species in seawater measured by macroalga (Laminaria japonica) uptake

The bioavailability of iron in seawater filtered through a 0.025-m filter was investigated using ⁵⁹Fe-labeled iron uptake by the macroalga Laminaria japonica (Areschoug: Phaeophyta) (collected in the northern Japan Sea 1993) as an assay. About 80% of the iron in the 0.025-m filtered coastal seawater was soluble and/or small colloidal organically bound iron, associated with natural organic ligands forming complexes with ferric ion. After decomposition of the organic matter by ultraviolet (UV) irradiation, 55% of the iron addition [or 0.6 nM, nearly the concentration of Fe(OH) ₂ ⁺ in equilibrium with amorphous hydrous ferric oxide in seawater at pH 8.0] in the 0.025-m filtered coastal seawater was taken up by the macroalga. Since the iron concentrations in the 0.025-m filtered coastal seawater are 0.1 to 2.0 nM and only 0.6 nM of the iron is likely available to biota over 1 to 2 d, we suggest that only small amounts of bioavailable iron exist in coastal seawater not affected by inflow from land and that a significant fraction of dissolved (<0.025 ) iron occurs in forms, such as organic iron complexes, other than the simple hydroxo-complex species predicted by thermodynamic models.     

Allocation of organic material and energy to the holdfast,stipe, and fronds inPostelsia palmaeformis (Phaeophyta: Laminariales) on the California coast

Postelsia palmaeformis were collected from the lower intertidal at Pigeon Point, California, USA, in May 1987, and the proximate composition and allocation of energy to the various body components were determined. The holdfast and stipe have a proximate composition (% dry weight) of ca. 40% ash, 5.3% protein, 1% lipid, 2% soluble carbohydrate, and 55% insoluble carbohydrate. The fronds have a proximate composition of ca. 25% ash, 6.5% protein, 2% lipid, 3% soluble carbohydrate, and 65% insoluble carbohydrate. The energetic level was ca. 12 kJ g^-1 dry wt and ca. 19 kJ g^-1 ash-free dry wt. The relative proportion of three plant components varied, comprising 26, 39, and 35% wet wt and 20, 42, and 38% kJ for the holdfast, stipe, and fronds, respectively. A plant with a basal stipe diameter of 33 mm contains 114 g wet wt and 266 kJ. The maximal density found in May 1987 was 826 plants, 49 301 g wet wt, and 106 157 kJ m^-2.P. palmaeformis differs in these characteristics from another intertidal pheophyte,Durvillaea antarctica, that is found in a high-energy intertidal zone.     

Influence of local environmental conditions on the seasonal acclimation process and the daily integrated production rates of Laminaria digitata (Phaeophyta) in the English Channel

Two populations of Laminaria digitata (Hudson) Lamouroux (Ann Mus Hist Nat Paris 20:21–47, 1813) were examined for their seasonal photosynthetic acclimation to clear and turbid-light environments along the French coast of the English Channel. Photosynthesis–irradiance curves, pigment concentrations and the daily in situ integrated oxygen production rates were measured in both populations. Despite the great differences in light attenuation between the sites, the two populations achieved similar oxygen production rates in the field, in relation to high maximal photosynthetic rates, total pigment concentrations and antenna (fucoxanthin + chlorophyll c)/chl a pigment ratios in sporophytes from the turbid environment. Environmental conditions (i.e. light, temperature and nitrogen availability) changed throughout the year in both sites. While the seasonal acclimation trends were evident in the clear-light environment, the strategy in the turbid-light environment differed, tending to maximize light capture throughout the year. This study highlights the diversity of the response of a single species to contrasted light environments.     

Morpho-functional patterns of photosynthesis and UV sensitivity in the kelp <Emphasis Type="Italic">Lessonia nigrescens</Emphasis> (Laminariales,Phaeophyta)

The photosynthetic responses of the south Pacific kelp Lessonia nigrescens of the coast of Valdivia, Chile (40°S), were investigated by exposing its different thallus parts, fronds, stipes and holdfasts, to UV radiation in the laboratory. Biologically effective doses (BED_{photoinhibition300}) between 400 and 800 kJ m⁻² were required for a 40% inhibition in photosynthesis under UVA+UVB radiation. At BED_{photoinhibition300} close to 250 kJ m⁻² (in treatments without UVB), the inhibition of photosynthesis did not exceed 20%. These UV doses were in the range of current daily doses measured in Valdivia on cloudless summer days. In general, exposure to UVB for periods longer than 12 h reduced photosynthesis, measured as maximal quantum yield (F _v/F _m) and electron transport. The fronds were the most UV-sensitive section of this alga, coinciding with the highest pigments contents and carbon fixation. Evidence of a photodamage was also seen. After a 48 h exposure to PAR+UVA+UVB, a decrease of F _v/F _m in the fronds was close to 41%, while in the stipes and holdfasts it was 12 and 18%, respectively. Although the thalli from the different size classes showed marked differences in their morphology and morphometry, no obvious differences in the UV tolerance of the fronds were detected. The results indicated that the UV-related responses are integrated in the suite of morpho-functional adaptations of the alga. Although the fronds are spatially more exposed to solar radiation than basal structures (stipes and holdfast), due their high turnover rate they may compensate better detrimental effects of UV. In contrast, stipes and the holdfast are key support structures characterized by low replacement rates and designed to confer hydrodynamic resistance to drag forces.     

Parthenogenesis,apogamy and apospory in Alaria crassifolia (Laminariales)

In cultures of Alaria crassifolia Kjellman, unfertilized eggs developed normally into haploid sporophytes which differentiated into a holdfast, stipe and blade with a midrib. The terminal cells of a male gametophyte grew apogamously into haploid sporophytes with narrow blades which lack the midrib. Further, diploid gametophytes were formed by apospory from vegetative cells of a diploid sporophyte. They were monoecious and their fertilized eggs developed into tetraploid sporophytes. Nuclear phases of the sporophytes and gametophytes concerned were confirmed by cytological observations.This work was supported by Grant No. 38803 from the Ministry of Education of Japan.     

三种水生植物对不同形态氮素吸收动力学研究

进行水生植物对NH4 和NO3-吸收动力学的研究.目的在于进行水体的生态修复时,可以根据不同营养状况的富营养化水体而选择相应的养分吸收效率的水生植物.该研究中比较了3种水生植物黄花水龙(Jussiaea stipulacea Ohwi)、伊乐藻(Elodea nuttallii)、凤眼莲(Eichhornia crassipes)对于铵态氮和硝态氮吸收动力学特征.结果表明:漂浮植物黄花水龙和凤眼莲具有较大的吸收速率Vmax和Km值,因此,它们更适合作为先锋植物对污染严重的富营养化水体进行前期的修复治理,待水体水质提高到一定的程度时,再利用去污能力低的沉水植物进行对修复水体水质的维持和提高,并在此基础上可逐步建立一个较为稳定的、生物多样性的生态系统.由于沉水植物伊乐藻对铵态氮和硝态氮的吸收有较低Km值和Vmaz值,因此更适合对轻度污染的富营养化水体直接应用伊乐藻来去除养分和维持水体水质.     

Influence of ultraviolet-radiation on chlorophyll fluorescence and growth in different life-history stages of three species of Laminaria (phaeophyta)

Zoospores, gametophytes, young sporophytes and discs cut from mature sporophytes of Laminaria digitata, L. hyperborea and L. saccharina were exposed in the laboratory to UV-radiation, with a spectral composition and irradiance similar to natural sunlight, for periods ranging from 15 min to 8 d, and were then returned to white light. Germination of zoospores and the growth of gametophytes were reduced after exposures to UV longer than 1 h, whereas UV had little effect on the growth of young or mature sporophytes unless exposure continued for more than 48 h. The variable fluorescence (F _v:F_m) of all stages was strongly reduced immediately after short exposures to UV, but recovered almost completely within 24 h. However, exposure of gametophytes to UV for >4 h resulted in little or no recovery of F _v:F_m, whereas >16 h of UV were required to produce this result in young sporophytes, and >48 h in mature sporophytes. Thus, sensitivity to UV-radiation decreased from gametophytes to sporophytes, and with increasing age of sporophytes, but, in gametophytes, growth appeared to be a more sensitive indicator of UV-damage than F _v:F_m after 24 h recovery. The responses to UV of the zoospores and gametophytes of all three species were similar, but both growth and fluorescence measurements suggested that the sporophytes of L. saccharina were more sensitive to UV than those of the other two species.     

Growth of juvenile Macrocystis pyrifera (Laminariales) in relation to environmental factors

Instantaneous relative growth rates, (d^-1), were measured for juveniles of the giant kelp Macrocystis pyrifera transplanted to study sites in Southern California kelp forests between 1978 and 1982. Growth rates ranged from negative values (indicating loss of tissue) to 0.03 (doubling of total frond length every 19 d). Multiple regression analysis of growth versus irradiation, temperature, nitrogen concentration and amount of fouling revealed that all these factors had significant effects, together accounting for about 50% of the total variance. Elevated irradiation and nitrogen levels had strongly stimulatory effects (tissue nitrogen may have been more critical than ambient nitrogen for growth), while high temperature and fouling had strongly inhibitory effects. Irradiation was the most important factor influencing growth in 6 of the 8 transplant experiments. During these 6 experiments, the compensating irradiation level (below which there was no growth) was between 0.4 and 0.7 E m^-2 d^-1, and saturating irradiation was between 2 and 3 E m^-2 d^-1. During two of the experiments, growth was apparently limited by extremely high temperatures or low nitrogen levels. Quantum irradiation levels in the kelp forest were generally between the compensation and saturation levels. However, irradiation levels occasionally dropped below the compensation point for several months. Irradiation was occasionally low enough to limit the distribution of juvenile kelp by inhibiting growth, especially in the deeper portions of the kelp forest and under dense canopies formed by adult plants.     

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.     

Heavy metals uptake from aqueous solutions using marine algae (Colpomenia sinuosa): kinetics and isotherms

The adsorption of copper, zinc, cobalt, lead and cadmium ions onto Colpomenia sinuosa was studied as a function of contact time, initial metal ion concentration and initial pH. In addition, desorption studies were performed. Characterisation of this adsorbent was also confirmed by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) analysis. Batch adsorption experimental data were analysed using Langmuir, Freundlich and Dubinin–Raduschkevich (D–R) adsorption isotherms. The results indicated that the biosorption equilibrium was well described by both the Freudlich and D–R isotherms. Moreover, sorption kinetics was performed and it was observed that equilibrium was reached in<60 min, which could be described by the pseudo-second-order kinetic model for all heavy metals. The sorption of heavy metals onto the biomass was largely dependent on the initial solution pH. The elution efficiency for heavy metal ions desorption from C. sinuosa was determined for 0.1 M HCl, 1.0 M HCl and 1.0 M HNO₃. Desorption efficiency and also adsorption capacity were highest for Pb(II). The results indicate that C. sinuosa has great potential for the removal of heavy metals in an ecofriendly process.     

Morphological and DNA sequence variation in the kelp Costaria costata (Phaeophyta)

Kelp species show substantial intraspecific morphological variation. The annual kelp, Costaria costata (C. Agardh) Saunders, is found in the lower intertidal and subtidal regions of shores which vary in exposure from strongly wave-exposed to sheltered. Phenotypic variation was studied in this monotypic genus. Individuals of C. costata were collected from two morphologically-distinct populations (one wave-exposed and the other wave-sheltered) at Cape Beale and Stanley Park, Vancouver, Canada, in May 1985. Analysis of morphological variation, using multivariate statistical techniques, indicated significant differentiation between plants from the two sites. Blade widths and thicknesses were the major discriminating variables. Restriction fragment length polymorphism (RFLP) analysis of nuclear DNA with 42 anonymous probes demonstrated one polymorphism. Most of the probes are hypothesized to encode highly repeated, dispersed sequences. These repeat sequence probes comprised 80.9% of all cloned fragments. Primary sequence analysis of 1595 base pairs of small-subunit ribosomal DNA and 204 base pairs of upstream sequence (probe pCc 18) failed to show any divergence between plants from the two sites.     

Light and temperature requirements for growth and reproduction in gametophytes of Ecklonia maxima (Alariaceae: Laminariales)

The morphological and reproductive development of gametophytes of Ecklonia maxima (Osbeck) Papenf. has been studied in vitro under a wide range of light and temperature conditions, and the results related to the natural environment over the range of the distribution of the species. Initial vegetative growth was light saturated at 20 E m^-2 s^-1, and maximal at 17.5° and 20°C. Most rapid egg production corresponded to low cell number of female gametophytes, and this process was light saturated at 60 E m^-2 s^-1, and optimised at 15° and 17.5°C. Cell number was also low at lower temperatures, with reduced fertility rates. Sub-saturating irradiances and supraoptimal temperatures caused females to become filamentous, producing many more cells, and reducing reproductive rates. The final egg production per female was, however, greater in these sub-optimal conditions, and this phenomenon is interpreted as an ecological adaptation which improves survival prospects in conditions prevailing at the fringes of the depth and geographical distribution of the species. The optimal, and maximum (22.5°C) temperatures for reproduction are far higher than those of northern hemisphere Laminarians. E. maxima is very much a warm temperate organism, and this could have implications for marine phytogeographical studies on the west coast of southern Africa.     

Transversal profiles of carbon assimilation in the fronds of three Laminaria species

The brown macroalgae Laminaria digitata (Huds.) Lamour., L. hyperborea (Gunn.) Foslie, and L. saccharina (L.) Lamour. (Laminariales, Phaeophyceae) have been investigated for carbon assimilation and assimilate biosynthesis in different tissues (meristoderm, cortex, medulla) of stipes and blades. Carboxylation via ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) and phosphoenolpyruvate carboxykinase (EC 4.1.32) follows a transversal gradient from the outer to the inner tissues with maximum activity of enzymatic CO₂ fixation in the meristoderm. Such transversal profiles are also recorded for photosynthetic and dark carbon assimilation as well as for kinetics of assimilate ¹⁴C-labelling in isolated tissues. Differential chemical constitution of the blade and stipe tissues examined and results from assimilate biosynthesis are discussed with regard to a transversal translocation of photosynthates from meristodermal to cortical and medullar cells.     

Ammonium excretion in a temperate-reef community by a planktivorous fish,Chromis punctipinnis (Pomacentridae), and potential uptake by young giant kelp,Macrocystis pyrifera (Laminariales)

The blacksmith Chromis punctipinnis, an abundant planktivorous damselfish off southern California, USA, shelters along rocky reefs at night. While sheltered, blacksmiths excrete ammonium that could, in turn, be utilized by nearby benthic macrophytes. Laboratory experiments during the summer and fall of 1983 and 1984 indicate that ammonium excretion at night ranged from 18.1 mol h^-1 by a 8.5 g (dry) fish, to 89.1 mol h^-1 by a 27.3 g fish; excretion rates generally declined throughout the night. Field measurements at night indicate that ammonium concentrations were significantly higher in rocky crevices occupied by blacksmiths than in unoccupied shelters, and the ammonium level in one shelter dropped after a blacksmith was experimentally removed. Young kelp plants (Macrocystis pyrifera) are capable of taking up ammonium at night. Ammonium levels in chambers containing both a blacksmith and a young kelp plant were significantly lower than in chambers containing only a fish, and ammonium levels dropped in ammoniumspiked chambers that contained kelp plants. Nighttime ammonium uptake rates by young kelp plants, which averaged 1.6 mol g^-1 (dry) h^-1, were only slightly lower than those during the day. Daytime excretion by blacksmiths occasionally results in elevated ammonium levels in the water column. On two of six days, ammonium concentrations in midwater foraging aggregations were slightly but significantly higher than in upcurrent controls; since blacksmiths typically aggregate at the incurrent margin of kelp beds, the ammonium is swept downcurrent and may be utilized by large M. pyrifera that extend through the water column. Thus, the activities of blacksmiths may results in the importation of extrinsic, inorganic nitrogen to primary producers on temperate reefs.     

Morphological variation and life history in cylindrical forms of Scytosiphon lomentaria (Scytosiphonaceae: Phaeophyta) from southern Australia

Variation amongst wild populations of Scytosiphon lomentaria (Lyngbye) Link is shown to be of a continuous nature, and the species cannot be readily segregated into distinct subspecific taxa on the basis of morphological characteristics. Zoospores derived from plurilocular sporangia developed asexually into cylindrical thalli under long and short days at 16°C. The progeny of some cylindrical thalli included microthalli bearing plurilocular sporangia or unilocular sporangia. Cylindrical forms of S. lomentaria were obtained in culture from wild microthalli of two kinds, bearing either plurilocular or unilocular sporangia. The microthalli differ morphologically from the ralfsioid stages commonly known to be plethysmothalli and sporophytes of S. lomentaria, but closely resemble the microthalli derived from cultures of wild S. lomentaria.     

Temperature tolerances of two southern African Ecklonia species (Alariaceae: Laminariales) and of hybrids between them

The temperature tolerances in culture of Ecklonia maxima (Osbeck) Papenf., the dominant kelp in the Benguela upwelling region on the west coast of southern Africa, and the smaller E. biruncinata (Bory) Papenf., growing on the warmer south coast, have been investigated. Vegetative growth and reproduction of gametophytes show very similar patterns in the two species, although temperature optima in E. biruncinata are consistently 2 ° to 3 °C higher than those of E. maxima. Reciprocal crosses between clonal female and male gametophytes of the two species produced healthy juvenile sporophytes, indistinguishable from the parent crosses. All parents and hybrids grew well over a wide range of temperatures (8 ° to 22°C), with E. biruncinata sporophytes again having slightly higher optima than E. maxima. Both reciprocal crosses exhibited optima intermediate between the parent crosses. The results are discussed with respect to the origins and evolution of Ecklonia species in the region.