PHOSPHOENOLPYRUVATE CARBOXYKINASE ACTIVITY IN ASCOPHYLLUM NODOSUM (PHAEOPHYCEAE)1

PEP-dependent⁴ CO₂-fixation by extracts of Ascophyllum nodosum (L.) Le Jol. is reported. The carboxylation of PEP is Mn²⁺ dependent and ATP is shown to be a product. IDP was found to be less efficient as a phosphate acceptor than ADP and 3-mercaptopicolinic acid inhibited the carboxylation reaction. Extracts decarboxylated OAA only in the presence of ATP and had high activities of MDH and GOT. This evidence, together with the probable absence of PEPC, PEPCTrP, and PC in A. nodosum extracts, favors the view that PEPCK is responsible for the light-independent CO₂-fixation observed in this alga.     

PROPERTIES OF PHOSPHOENOLPYRUVATE CARBOXYKINASE FROM ASCOPHYLLUM NODOSUM (PHAEOPHYCEAE)1

Phosphoenolpyruvate carboxykinase was purified to electrophoretic homogeneity from the brown alga. Ascophyllum nodosum (L.) le Jol. Its molecular mass was 60 kDa as determined by gel filtration. The pH optimum of the carboxylating reaction was 7.9 and the apparent K_m for PEP⁴, ADP and HCO₃^- were 0.036, 0.0116 and 50 mol · m^-3, respectively. Rates of light and dark carbon fixation are also reported for A. nodosum apices and it is shown that rates of in vitro PEPCK activity would account for the observed rate of dark fixation. The physiological role of PEPCK is discussed in relation to light-independent carbon fixation.     

PHYSIOLOGICAL AND POPULATION ECOLOGY OF INTERTIDAL AND SUBTIDAL ASCOPHYLLUM NODOSUM (PHAEOPHYTA)1

Morphological, demographic and physiological characteristics of Rhode Island intertidal and subtidal populations of Ascophyllum nodosum (L.) Le Jolis were compared in order to examine factors influencing vertical distribution. The two populations had distinctive morphologies: subtidal plants were narrower (more terete) and highly branched compared with intertidal plants. The subtidal population showed signs of necrosis and breakage, which was reflected in significantly shorter mean plant size. High survivorship and low recruitment of both population resulted in relatively constant densities, averaging 91 and 50 plants per m² in the intertidal and subtidal habitats, respectively. Intertidal plants had higher mean annual growth rates (25 cm.yr^?1) than subtidal plants (2 cm.yr^?1). In general, intertidal plants had higher photosynthetic capacity and nutrient (NO₃^?) uptake rates than the subtidal population but maintained lower light-harvesting pigment and tissue nitrogen concentrations. Although Ascophyllum nodosum is capable of survival and growth in subtidal as well as intertidal areas, results of this study suggest that different selective pressures affect persistence in each habitat. The scarcity of plants in the subtidal environment may be due to the lack of a critical balance between algal production, allocation of photosynthate, and the negative effects of grazers or competitors.     

SETTLEMENT AND SURVIVAL OF POLYSIPHONIA LANOSA (CERAMIALES) SPORES ON ASCOPHYLLUM NODOSUM AND FUCUS VESICULOSUS (FUCALES)1

The settlement patterns of spores of Polysiphonia lanosa (L.) Tandy on Ascophyllum nodosum (L.) Le Jolis and Fucus vesiculosus L. were studied using a flow tank. Settlement sites were defined as ‘sheltered’ or ‘exposed.’ Surface area calculations revealed non-random settlement on A. nodosum, with higher than expected spore frequencies on the thallus and lateral pits and lower than expected frequencies on the vesicles. Settlement of F. vesiculosus was random and significantly lower than on A. nodosum. On the shore, survival of sporelings from September (post-sporulation) to May (pre-sporulation) was highly non-random on both basiphytes. On A. nodosum, lateral pits ('sheltered') showed the highest survival frequency. Here the proportion of surviving sporelings increased over the study period, whereas the proportion on open thallus area ('exposed') decreased. On F. vesiculosus also preferential survival occurred on ‘sheltered’ sites such as vesicle/thallus interfaces and wounds. Between September and May, all P. lanosa sporelings were lost from ‘exposed’ areas (thallus surface and vesicles). Overall, frequencies of surviving sporelings were much greater on A. nodosum than on F. vesiculosus. These results are discussed with reference to basiphyte morphology, epiphyte removal mechanisms and the survival stratagy of P. lanosa.     

COLONIZATION AND GROWTH OF ASCOPHYLLUM NODOSUM (PHAEOPHYTA) IN MAINE1

Colonization and growth of Ascophyllum nodosum (L.) Le Jol. were investigated in two Maine estuaries from 1972 to 1978. Following denudation of intertidal rock, substrata were initially colonized by Fucus vesiculosus L.; eventually, Ascophyllum supplanted Fucus, and became dominant in terms of percentage cover. Ascophyllum settled first and most densely in the low intertidal zone, but its fastest growth occurred in the mid-intertidal zone. Some, but not all, Ascophyllum germlings produced a vesicle within one year of colonization. The mean annual growth of A. nodosum was variable among sites, zones and years.     

A MODEL FOR GAMETE RELEASE IN ASCOPHYLLUM NODOSUM (PHAEOPHYTA)1

The question of what controls gamete release in Ascophyllum nodosum (L.) Le Jolis was studied at six sites along the central coast of Maine. Percent release was assessed weekly along randomly marked transect lines in the mid-intertidal zone. Six independent variables–water temperature at high tide, air temperature at low tide, nitrogen (ammonia, nitrite, and nitrate), and salinity–were measured concurrently. Stepwise multiple regression analysis on the percentage of plants having released gametes revealed that water temperature at high tide accounted for most of the among-site variation (R²= 0.77) in the timing of release. The addition of Julian day increased the R² to 0.82; no other variables were significant. Probit analysis, based on water temperature at high tide, generated an environmentally realistic model for predicting gamete release. The model predicts the onset, midpoint, and termination of gamete release at 6, 10, and 15°C, respectively, and the midpoint at a cumulative water temperature of 358°C. This model has value for developmental studies and, potentially, for reseeding A. nodosum populations. Probits may be useful for characterizing phenological events in other fucoids and algal species.     

DARK CARBON FIXATION STUDIES ON THE INTERTIDAL MACROALGA ASCOPHYLLUM NODOSUM (PHAEOPHYTA) 1

The characteristics of dark carbon fixation by Ascophyllum nodosum were investigated. In longitudinal profile the maximum rates of dark and light dependent fixation are found at the apex. The use of Michaelis-Menten kinetics did not suitably describe the relationship between the uptake rate in the dark and the total inorganic carbon concentration. Dark fixation was saturated at a total inorganic carbon concentration [TIC] of 2.5 mM. The use of the Hill-Whittingham equation to describe the uptake curve indicates that the process is diffusion limited. Comparisons of dark fixation at high (8.0) and low (5.2) pH suggest that bicarbonate ions are used as a source of inorganic carbon. The transfer of ¹⁴C, fixed in the dark, from the ethanol soluble to the insoluble fraction was relatively slow irrespective of the light treatment during the chase period. Ascophyllum nodosum displays a small diel fluctuation in the pH of aqueous extracts and titratable acidity similar to that displayed by CAM plants. The significance of dark fixation to the overall carbon budget is discussed.     

SPATIAL DYNAMICS OF A HIMANTHALIA ELONGATA (FUCALES, PHAEOPHYTA) POPULATION

In dense monospecific stands of plants intraspecific competition usually results in self-thinning, the concurrent increase in biomass and decrease in density over time. Self-thinning may also result in a change in the spatial pattern of individuals, but so far the spatial dynamics of marine plants has not been investigated. The brown alga Himanthalia elongata ( L.) S. F. Gray forms dense monospecific stands on many northern temperate rocky shores, and various attributes (including its simple form) facilitated the study of the spatial dynamics of this species .
The spatial pattern of settling zygotes was examined in the laboratory. In the absence of water movement, substratum heterogeneity, and a point source, zygotes usually settled in clumps rather than randomly. Within the clumps zygotes appeared to be regularly distributed at a scale similar to the size of the zygotes themselves. Furthermore, the clumps themselves seemed to be regularly distributed. On the shore, well-established stands of "button-stage" Himanthalia populations were examined during a period of extensive growth and self-thinning. Individual plants were initially highly regular in spatial pattern but became less so over time. The pattern of plants dying during self-thinning was also highly regular and probably reflected existing spatial regularity. However, using a hypothesis of mortality as a random event, I found that smaller plants had a less than average survival potential, while larger plants had a greater than average chance. A consideration of the spatial pattern of plants alive at the end of the study revealed regularity at a scale of 2–7 mm but a random spatial pattern at larger scales, which might indicate a small sphere of influence of competing individuals. The best predictor of mean nearest neighbor distances in the populations was mean plant diameter .     

NEW RECORDS OF ASCOPHYLLUM NODOSUM (L.) LE JOL. FROM THE WARMER PARTS OF THE ATLANTIC OCEAN1

Floating plants of Ascophyllum nodosum (L.) Le Jol. have been found for the first time at 00°47'S, 14°10'W to 01°21'S, 13°32'W. Populations of attached individuals do not occur below 40°N, although previous records of drift plants are known from further south. The plants found near the equator have probably arisen from attached populations in western Europe.     

镜湖花臂尾轮虫夏季种群内不同克隆的生活史特征

应用生命表统计学等方法对镜湖花臂尾轮虫夏季种群内4个在生化遗传特征上互不相同的克隆(克隆A、B、C和D)在4种温度(15℃、20℃、25℃和30℃)下的生活史特征及其对升高的温度的反应进行了比较研究。结果表明,温度对花臂尾轮虫存活率和繁殖率的影响在不同克隆间存在着差异。20℃和25℃下,4个克隆轮虫的世代时间和净生殖率均分别无显著的差异;20℃、25℃和30℃下,4个克隆轮虫的平均寿命和出生时的生命期望亦然。其余各温度下,4个克隆间轮虫的其他生命表参数均有显著的差异。20℃、25℃和30℃下,4个克隆轮虫所产后代中的混交雌体百分率间均具有显著的差异,且克隆C轮虫所产后代中的混交雌体百分率最高。15℃下,克隆D轮虫的个体适合度最高;25℃下,克隆A和B轮虫的个体适合度较高。4个克隆轮虫的生活史特征对升高的温度的反应也存在着差异。忽略温度的影响时,4克隆间,克隆D轮虫的世代时间、平均寿命和出生时的生命期望最短,净生殖率、种群内禀增长率和个体适合度均最低;克隆C轮虫所产后代中的混交雌体百分率最高。30℃下,4个克隆轮虫的种群内禀增长率存在着差异可能是不同基因型的轮虫克隆群在种群内所占的比例不同的重要原因;而它们的个体适合度相似则可能是不同基因型的轮虫克隆群在夏季镜湖中共存的主要原因之一。     

ASCOPHYLLUM NODOSUM (PHAEOPHYTA) IN AXENIC CULTURE AND ITS RESPONSE TO THE ENDOPHYTIC FUNGUS MYCOSPHAERELLA ASCOPHYLLI AND EPIPHYTIC BACTERIA1

Ascophyllum nodosum (L.) Le Jol. was freed from bacteria and the endophytic fungus Mycosphaerella ascophylli Cotton by repeated treatment with chlorine solutions and grown in artificial seawater. Two types of axenic culture of different origin were obtained. Type 1 was developed from apices of A. nodosum collected in the sea. Type 2 was from plants which developed from adventitious embryos on rhizoids formed by type 1. This is the first time A. nodosum has been cultivated axenically. Growth of the axenic alga was increased by IAA, 21P and zeatin. Without external growth regulators some strains of the axenic alga deteriorated within a year; others developed a filamentous habit. Sulfur in a reduced state also stimulated growth. Addition of either glucose, mannose or mannitol to the medium caused the formation of calluslike layers of loosely packed colorless cells under the epidermis of the thalli and the epidermis was sloughed off. No increase in thallus length was noticed. Mycosphaerella ascophylli in axenic culture did not excude any substances stimulating growth of the alga, but that does not exclude an influence of the fungus on the alga in vivo. The fungus, when growing within the alga, seemed to have little influence on algal morphology. A bacterized but fungus-free A. nodosum was cultivated in an artificial seawater for 8 years. In the bacteria-free alga, the fungus protruded from the epidermis and evidently utilized the alga as a carbon source. The bacteria thus seem much more important than the fungus for normal growth of the Ascophyllum plant.     

THE DISTRIBUTION OF PHOTOSYNTHATE IN ASCOPHYLLUM NODOSUM AS IT RELATES TO EPIPHYTIC POLYSIPHONIA LANOSA12

The brown alga Ascophyllum nodosum is not a major source of organic carbon for its epiphytic red alga Polysiphonia lanosa. Plants pulse-labeled for 24–25 hr with NaH¹⁴CO₃ were examined for exudation and translocation. The maximum amount of radioactive carbon compounds lost from A. nodosum during this experimental period was less than 0.3% of the total ¹⁴C fixed by the alga, and of this amount, only 5% could, have moved through the frond. The remaining fraction of the ¹⁴C lost from the thallus was released into the water. The total exudate from A. nodosum was collected for 1 week in a series of flasks of filtered seawater changed at 12-hr intervals corresponding with the beginning of the light and dark periods, respectively. During 7 days at 15 C only 1.5% of the total ¹⁴C originally fixed had been released as radioactive organic carbon, whereas at 5 C, 0.6% of the total ¹⁴C fixed was found in the medium. No significant difference in the rate of exudation of organic ¹⁴C was observed in light or darkness. After fractionation of the exudate it was found that only 10% of the radioactivity in these exudates was composed of organic acids or amino acids. P. lanosa, on the other hand, is perfectly capable of fixing its own carbon. The photosynthetic rates measured by H¹⁴CO₃ uptake confirm the observations of Bidwell: 3.96 mg CO₂/g/hr (0.09 m mole/g/hr).     

GENETIC VARIATION AND POPULATION STRUCTURE IN THE FERN BLECHNUM SPICANT (BLECHNACEAE) FROM WESTERN NORTH AMERICA

Population genetic structure in the homosporous fern Blechnum spicant was analyzed in six populations from western North America. Each population was divided into approximately 10 m by 10 m subpopulations, and genetic variation within and among subpopulations was compared using enzyme electrophoresis and F statistics. These analyses indicated that there was no evidence of genetic structure in four of the six populations examined. However, significant genetic heterogeneity among subpopulations was observed for the other two populations. The genetic structure of these populations may be attributable, in part, to family structure resulting from high rates of intragametophytic selling and/or spatial patchiness in the distribution of individuals due to limited habitat availability in these areas. Outcrossing populations of B. spicant generally lack genetic structure, whereas the most highly inbreeding population maintains significant genetic structure. The information obtained in this investigation of population genetic structure in Blechnum spicant is consistent with data for angiosperms and gymnosperms. It appears that the outcrossing mating system and effective mechanism of spore dispersal in B. spicant may account for the general lack of genetic structure within populations of this species.     

ECOLOGY AND NATURAL HISTORY OF IRIDAEA CORDATA (RHODOPHYTA; GIGARTINACEAE): POPULATION STRUCTURE1

The population structure of 4 California Iridaea cordata (Turner) Bory populations was studied. Random sampling procedures were used to measure seasonal variations in standing crops, density and size-class distribution of life history stages. The results describe aspects of the in situ life history; a prerequisite to realistically considering the distribution, ecology or life history expressions of an alga. Seasonal fluctuations in density occur only in the juvenile stage, which is initiated during the winter (November to January) predominantly from the basal perennial crusts. Both the gametangial and tetrasporangial stages are present throughout the year. The tetrasporangial stage is dominant in relation to the sexual stages in both density and biomass during most of the year, except spring when the new crop in just maturing and all stages are abundant. Density in nearly constant and observable changes in the populations are due to biomass fluctuations. Seasonal lows in biomass occur during the winter with the majority of thalli in the smaller size-classes. Growth and maturation culminate in peak summer crops and dominance of the tetrasporangial stage, followed by autumnal senescence and die-back in winter. Carrageenans analyzed from immature thalli showed a predominance of lambda-type, previously determined as specific for tetrasporangial plants. This indirect evidence for the tetrasporangial nature of immature plants suggests that dominance of the diploid stage occurred prior to blade development and most likely at the spore level. Alternatively, field results indicate a major contribution and possible replacement of alternation of gametangial and tetrasporangial stage by thallus perennation and vegetative reproduction.     

GENETIC DIVERSITY AND POPULATION STRUCTURE IN TRADESCANTIA HIRSUTICAULIS (COMMELINACEAE)

Tradescantia hirsuticaulis, the hairy-stemmed spiderwort, is an insect-pollinated perennial plant species found primarily on rock outcrops in Georgia, South Carolina, and Alabama. Although populations of T. hirsuticaulis are rare and scattered, local populations are frequently large. Levels of genetic variation were assessed for 13 populations representing the species' range in these three states. Despite the disjunct distribution of this habitat specialist and apparent lack of specialized seed and pollen dispersal mechanisms, exceptionally high levels of genetic variation are maintained within the species, with a moderate level of variation (18%) found among populations. Twenty-nine of the 33 loci resolved (88%) were polymorphic within the species; the mean number of loci polymorphic within populations was 54%. The mean number of alleles per polymorphic locus was 3.24 across all populations and averaged 2.37 within populations. Genetic diversity was 0.206 for the species, whereas mean population genetic diversity was 0.157, both much higher than the average for other short-lived herbaceous perennials. Estimated levels of gene flow were moderate (Nm = 0.95), and a significant association between geographic distance and genetic distance between populations was found (r = 0.68; P < 0.0001). Habitat destruction is the major threat to this genetically diverse species. Since gene flow among its highly dispersed populations is limited, diminution or extinction of local populations could jeopardize the long-term evolutionary potential of this species.     

ELECTRICAL IMPEDANCE IN ASCOPHYLLUM NODOSUM AND FUCUS VESTCULOSUS IN RELATION TO COOLING,FREEZING, AND DESICCATION1

Electrical impedance monitoring techniques appear to be useful in tracing the effect of cooling or desiccation upon the thallus of Fucus vesiculosus and Ascophyllum nodosum. These algae were found to be remarkably resistant to injury from freezing down to ?20 C even during midsummer and from desiccation up to 70% water loss, and in these properties were markedly different from land plants. Freezing point depressions, the degree of supercooling, activation energies of cooling-impedance curves, and the slope of these curves themselves were useful in disclosing differences between time of sampling, storage time, and indications of damage in tissue. No significant difference could be detected between the 2 species collected and tested at the same time. Significant differences occurred in F. vesiculosus between summer and winter, and in winter between submersed and intermittently exposed plants. Tracer ion uptake techniques confirmed that freezing to ?20 C did not kill tissues.     

MICROGEOGRAPHIC GENETIC STRUCTURE OF MORPHOLOGICAL AND LIFE HISTORY TRAITS IN A NATURAL POPULATION OF IMPATIENS CAPENSIS

To investigate the microgeographic spatial structure of genetic variation for quantitative traits in a natural population of Impatiens capensis, we performed a common-garden greenhouse experiment. Seedlings were collected at 10-m intervals from a 40 times 40-m permanent grid in a natural population and grown to maturity in a greenhouse. From these parents, 3 self-fertilized seed families per grid point were then grown in a randomized design in the greenhouse and scored for a variety of morphological and life-history traits. Virtually all of the traits displayed significant variation among families, and many were significantly heterogeneous among grid points, indicating microgeographic genetic differentiation on a fine spatial scale. Overall morphological divergence, measured as Mahalanobis distances between grid points, increased with geographical distance. In general, spatial autocorrelation coefficients of grid point character means were positive at 11–20 m and negative beyond 40 m, although power for significance testing was low. The first factor in a principal component analysis of grid point means was positively loaded on height-related traits and negatively loaded on total reproduction at 50 days, accounting for 31% of the variation. This factor displayed significant positive spatial autocorrelation at 11–20 m and negative autocorrelation at >40 m. The remaining factors showed no detectable spatial structuring among grid points. These differences in spatial pattern among characters suggest that forces other than drift may have influenced the genetic structure of the population. There was no evidence for density-dependent selection; seedling density was not significantly correlated with the grid point mean of any trait.     

GROWTH,YIELD AND MORPHOLOGY OF ASCOPHYLLUM NODOSUM (PHAEOPHYTA) UNDER CONTINUOUS AND INTERMITTENT SEAWATER SPRAY CULTURE REGIMENS1

Growth and yield of the brown alga Ascophyllum nodosum (Le Jolis) were measured under various regimens of seawater spray culture. One-hour periods of desiccation throughout the day and night and cessation of spray throughout the night did not affect growth relative to that in continuous spray. Desiccation for four hours during the day resulted in death. Changes in morphology from the normal intertidal growth form to that resulting from spray culture are described.     

POPULATION GENETIC STRUCTURE IN CHEILANTHES GRACILLIMA

Population genetic structure was examined in five populations of the xerically adapted homosporous fern Cheilanthes gracillima. F statistics using allozymic data indicated substantial genetic structure in all populations. To determine the factors responsible for genetic structure, we calculated levels of intragametophytic selfing and the fixation index for each subpopulation of each population and estimated levels of intrapopulational gene flow in each population. These analyses indicated that each subpopulation was a panmictic unit; thus, population genetic structure is not due to family structure, arising via matings between relatives. Intrapopulational gene flow was surprisingly low, given the typically high dispersibility of fern spores. However, it seems unlikely that spore dispersal in C. gracillima is significantly reduced relative to other homosporous ferns. Instead, we propose that the low rates of intrapopulational gene flow reflect limited availability of safesites for spore germination and gametophyte establishment. This ecological factor may play a primary role in generating and/or maintaining population genetic structure in C. gracillima.     

GENETIC DIVERSITY AND POPULATION STRUCTURE IN CAMELLIA JAPONICA L. (THEACEAE)

Camellia japonica is a widespread and morphologically diverse tree native to parts of Japan and adjacent islands. Starch gel electrophoresis was used to score allelic variation at 20 loci in seeds collected from 60 populations distributed throughout the species range. In comparison with other plant species, the level of genetic diversity within C. japonica populations is very high: 66.2% of loci were polymorphic on average per population, with a mean number of 2.16 alleles per locus; the mean observed and panmictic heterozygosities were 0.230 and 0.265, respectively. Genotypic proportions at most loci in most populations fit Hardy-Weinberg expectations. However, small heterozygote deficiencies were commonly observed (mean population fixation index = 0.129). It is suggested that the most likely cause of the observed deficiencies is population subdivision into genetically divergent subpopulations. The overall level of population differentiation is greater than is typically observed in out-breeders: The mean genetic distance and identity (Nei's D and I) between pairs of populations were 0.073 and 0.930, respectively, and Wright's Fst was 0.144. Differences among populations appeared to be manifested as variation in gene frequencies at many loci rather than variation in allelic composition per se. However, the patterns of variation were not random. Reciprocal clinal variation of gene frequencies was observed for allele pairs at six loci. In addition, principal components analysis revealed that populations tended to genetically cluster into four regions representing the geographic areas Kyushu, Shikoku, western Honshu, and eastern Honshu. There was a significant relationship between genetic and geographic distance (r = 0.61; P < 0.01). Analysis of variance on allozyme frequencies showed that there was approximately four times as much differentiation among populations within regions, as among regions. It is likely that the observed patterns of population relationships result from the balance between genetic drift in small subpopulations and gene flow between them.