Growth and productivity of the psychrophilic marine diatoms Thalassiosira antarctica Comber and Nitzschia frigida Grunow in batch cultures at temperatures below the freezing point of sea water

Summary The diatoms Nitzschia frigida and Thalassiosira antarctica grow exponentially even at temperatures between-4 and -6°C and a salinity between 73 and 100 Under these conditions the light saturation of growth is reached in continuous light at a scalar quantum irradiance of between 7 mol·m^–2·s^–1 and 10 mol · m^–2 · s^–1. The increase in salinity retards growth more than a decrease in temperature. For N. frigida the limit of growth is at -8°C (S = 145%.). At increasing quantum irradiance, the chlorophyll content per unit cell volume decreases, whereas there is a significant increase in the carbon content of the exponentially growing cells. In addition, there is hardly any change in the protein content. The results show that both species of diatom can survive in ice without forming resting spores and even grow at extremely low temperatures.     

The Use of the [13C]/[12C] Ratio for the Assay of the Microbial Oxidation of Hydrocarbons

The study deals with a comparative analysis of the relative abundances of the carbon isotopes ¹²C and ¹³C in the metabolites and biomass of the Burkholderia sp. BS3702 and Pseudomonas putida BS202-p strains capable of utilizing aliphatic (n-hexadecane) and aromatic (naphthalene) hydrocarbons as sources of carbon and energy. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of Burkholderia sp. BS3702 on n-hexadecane (¹³C = –44.6 ± 0.2) were characterized by the values of ¹³C_{CO 2} = –50.2 ± 0.4, ¹³C_biom = –46.6 ± 0.4, and ¹³C_exo = –41.5 ± 0.4, respectively. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of the same bacterial strain on naphthalene (¹³C = –21 ± 0.4) were characterized by the isotope effects ¹³C_{CO 2} = –24.1 ± 0.4, ¹³C_biom = –19.2 ± 0.4, and ¹³C_exo = –19.1 ± 0.4, respectively. The possibility of using the isotope composition of metabolic carbon dioxide for the rapid monitoring of the microbial degradation of petroleum hydrocarbons in the environment is discussed.     

Salinity-temperature tolerance of two closely related triclad species,Dugesia lugubris and D. polychroa (Turbellaria), in relation to their distribution in The Netherlands

The tolerance of adult specimens of Dugesia lugubris and D. polychroa for 13 different chlorinities ranging from 15.0–3.8 and for two temperatures, viz. 4 and 23 °C, was tested.At chlorinities of 7.5 and lower, the survival time of both species was considerably longer than at higher chlorinities (a few hours at 7.5, one to several days at 6.6 and lower concentrations). It is assumed that this is determined by the osmoregulatory capacity of the planarians.It was found that at low chlorinities combined with a high temperature D. polychroa survived longer than D. lugubris, while at the same chlorinities the opposite was true for a low temperature. The effect of temperature on survival at low chlorinities was more drastic for D. lugubris than for D. polychroa.The results correlate with data on the distribution of both species in The Netherlands. Outside areas with an average chlorinity below 2 the two species were rarely found.     

Growth rates and the salinity response of an Antarctic ice microflora community

Summary An ice microflora community collected from the bottom of seasonal pack-ice off the Amery Ice Shelf, Antarctica, was grown at salinities which varied from 11.5 to 34. The response exhibited by the community and by individual species was characterized by an initial lag phase-adaptation period followed by a short period of exponential growth. Doubling rates based on changes in chlorophyll a had a range from 0.05 to 0.23 day^-1 during the time required to reach maximum chlorophyll a concentration and a range of 0.04 to 0.42 day^-1 during a period of exponential growth. Exponential growth rates of individual species ranged from 0.2 to 1.0 doublings day^-1. Growth occurred at all salinities above 11.5. Community growth rates increased with increasing salinity, and the growth-salinity response of most species was shifted toward higher salinities suggesting that this Antarctic ice microalgal community was adapted to the ambient salinity regime: 34.     

Use of15N/14N rations to evaluate the food source of the mysid,Neomysis intermedia Czerniawsky,in a eutrophic lake in Japan

The stable isotope ratios of nitrogen were measured in the mysid,Neomysis intermedia, together with various biogenic materials in a eutrophic lake, Lake Kasumigaura, in Japan throughout a year of 1984/85. The mysid, particulate organic matter (POM, mostly phytoplankton), and zooplankton showed a clear seasonal change in ¹⁵N with high values in spring and fall, but the surface bottom mud did not. A year to year variation as well as seasonal change in ¹⁵N was found in the mysid. The annual averages of ¹⁵N of each material collected in 1984/85 are as follows: surface bottom mud, 6.3 (range: 5.7–6.9); POM, 7.9 (5.8–11.8); large sized mysid, 11.6 (7.7–14.3); zooplankton, 12.5 (10.0–16.4); prawn, 13.2 (9.9–15.4); goby, 15.1 (13.8–16.7). The degree of¹⁵N enrichment by the mysid was determined as 3.2 by the laboratory rearing experiments. The apparent parallel relationship between the POM and the mysid in the temporal patterns of ¹⁵N with about 3 difference suggests the POM (mostly phytoplankton) as a possible food source ofN. intermedia in this lake through the year.     

Vergleichende Untersuchungen zur Atmungsphysiologie euryhaliner Gammariden unter besonderer Berücksichtigung der Salzgehaltsanpassung

Zusammenfassung 1. Der respiratorische Stoffwechsel der euryhalinen AmphipodenGammarus locusta (L.),G. oceanicus Segerstråle,G. salinus Spooner,G. zaddachi Sexton undG. duebeni Lilljeborg wurde in einer Durchflußapparatur auf polarographischem Weg bei einer Temperatur von 15° C untersucht.2. Bei allen fünf Arten wurden die Beziehungen zwischen Sauerstoffverbrauch(y) und Körpergewicht (x) in Abhängigkeit vom Salzgehalt (30 und 10 ) geprüft und die Parameter der allometrischen Funktiony =a · x ^b ermittelt (vgl. Tab. 1).3. Der Regressionskoeffizientb, der die Größenabhängigkeit des Stoffwechsels kennzeichnet, weist artspezifische Unterschiede auf und ist abhängig vom Salzgehalt. Dieser zeichnet sich — mit Ausnahme vonG. duebeni — bei einer Salinität von 30 durch höhere Werte aus als bei 10 und ist in allen Fällen signifikant verschieden. Die Größenabhängigkeit des Stoffwechsels liegt im Bereich zwischen einer Gewichts-und einer Oberflächenproportionalität bzw. sogar darunter (b = 1-0,6).4. Ein interspezifischer Vergleich des Faktorsa, der die aus der Gesamtheit der Meßwerte berechnete Atemgröße von der Gewichtseinheit charakterisiert, ergibt, daß die Stoffwechselintensität in der Reihenfolge vonG. locusta überG. oceanicus, G. salinus, G. zaddachi bis zuG. duebeni fortschreitend abnimmt. Der durchschnittliche O₂-Bedarf von Flohkrebsen mit einem Lebendgewicht von 0,1 g reicht bei 30 von 17,1 mm³/h(G. locusta) bis zu 7,1 mm³/h(G. duebeni).5. Die Veränderungen des O₂-Verbrauchs nach einem sprunghaften Salinitätswechsel und der zeitliche Ablauf der Salzgehaltsanpassung wurden unter vergleichenden Gesichtspunkten untersucht. In Abhängigkeit von der Salinitätstoleranz der einzelnen Arten erfolgte eine Überführung von 10 in 30 , von 30 in 45 , von 30 in 10 und von 10 in 3 .6. Bei einem Wechsel aus verdünnten in konzentriertere Medien geht der Adaptationsprozeß wesentlich rascher vonstatten und ist mit geringeren Änderungen der Atmungsintensität verknüpft als bei Überführungen in umgekehrte Richtung. Die Anpassungszeiten bis zum Erreichen eines neuen, gleichbleibenden Stoffwechselniveaus liegen zwischen 3 und ungefähr 30 Stunden.G. duebeni verfügt über ein besseres Kompensationsvermögen als die anderen Arten, unter denenG. locusta die relativ geringste Regulationskapazität aufweist.7. Bei Nahrungsentzug sinkt die Stoffwechselrate. Messungen anG. oceanicus haben ergeben, daß die Atmungsintensität nach 20–24 Stunden gegenüber den Ausgangswerten um ca. 15 % abfällt und sich auch innerhalb der folgenden 5 Tage nur unwesentlich verringert.8. Der Aktivitätsstoffwechsel adulter Flohkrebse beträgt etwa das 2 1/2–3fache des Ruheumsatzes. Unter Grundumsatzbedingungen kann eine ausgeprägte Rhythmik der Ventilationsbewegungen der Pleopoden zutage treten.9. Während der Häutung nimmt die O₂-Aufnahme um das 2,2- bis 3,9fache des mittleren Normalverbrauchs zu. BeiG. locusta wurden die höchsten, beiG. duebeni die niedrigsten Stoffwechselsteigerungen verzeichnet.10. Verschiedene stoffwechselphysiologische Aspekte, insbesondere das Problem der Salzgehaltsanpassung und der damit verbundenen osmo- und ionenregulatorischen Prozesse, werden diskutiert. Die Stoffwechselleistungen der einzelnenGammarus-Arten werden verglichen und zu ihren Umweltansprüchen in Beziehung gesetzt.

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Comparative investigations on the respiratory physiology of euryhaline gammarids with special reference to salinity adaptation

Metabolic rates were measured of the euryhaline amphipodsGammarus locusta (L.),G. oceanicus Segerstråle,G. salinus Spooner,G. zaddachi Sexton, andG. duebeni Lilljeborg at 15° C by means of flow-through polarographic respirometry. The relationships between oxygen consumption (y) and body weight (x), expressed by the equationy = a · x ^b, under the influence of two salinities (10 and 30 ) were investigated. The regression coefficients (b), which describe the slopes of the regression lines, reveal significant differences for the salinities tested. Except forG. duebeni, higher values were obtained in 30 than in 10 . In the five species, metabolism as a function of size is characterized by regression coefficients ranging from 1 to 0.6. An interspecific comparison of the parametera, representing the intercept on they axis, exhibits a decrease in oxygen requirements in the orderG. locusta, G. oceanicus, G. salinus, G. zaddachi, G. duebeni. The respective values for 0.1 g (fresh weight) animals range from 17.1 to 7.1 mm³ O₂/h (30 ). Experiments on the alterations in metabolic rates following osmotic stress were designed to provide information on time course and capacity of adaptation to salinity. Depending on the salinity tolerances of the species, the responses after abrupt transfers from 10 to 30 , 30 to 45 , 30 to 10 and 10 to 3 were recorded. Changes from more concentrated to more dilute media induce less extensive alterations in respiratory rates and lead to faster adaptation to new salinity levels than transfers in the opposite direction. A new steady state of metabolic rate following salinity stress may be reached after 3 to about 30 hours.G. duebeni exhibits higher capabilities for compensatory adjustments than the other species.G. locusta was shown to be least capable of compensating for salinity changes. Oxygen consumption declines during starvation and attains a fairly constant level, reduced by ca. 15 %, 20 to 24 hours after the beginning of fast, as demonstrated inG. oceanicus by long-term experiments over 6 days. In adult individuals, activity metabolism exceeds standard rates by about 2 1/2 to 3 times. Under basal conditions, distinct respiratory ventilation rhythms of pleopod beating may occur. In addition, the time course of respiratory alterations during moulting was measured. At exuviation, oxygen uptake increases the mean respiratory rates 2.2 to 3.9 times. Some physiological and ecological aspects are discussed, mainly with respect to salinity adaptation and the processes of osmotic and ionic regulation involved. Metabolic rates of gammarid species are compared and related to environmental requirements. The similarity in the functional responses of the sibling speciesG. zaddachi andG. salinus is emphasized.

     

Effects of salinity on metabolism and life history characteristics of Daphnia magna

In the Baltic Sea area, the cladoceran Daphnia magna is commonly found in brackish water rockpools and it has been suggested that salinity is one of the niche dimensions that affects the distribution of the species. The salinity tolerance of D. magna was studied both in physiological and life history experiments. The experimental salinities were freshwater, 4S and 8S. The highest respiration and ammonium excretion rates were measured in the freshwater treatment with decreasing respiration and ammonium excretion rates at higher salinities. The lowest O/N ratio (oxygen consumption to ammonium excretion), describing the metabolic status of an organism, was obtained at 8S, although the only significant differences were detected when comparing to 4S treatments. Individual growth rate, reproductive output and population growth rate were highest at 4S. At 8S growth and reproduction were reduced as compared to freshwater and 4S. The life history parameters in the performed experiments indicated higher fitness (expressed as r) as well as more favourable conditions for growth and reproduction at 4S, whereas the O/N ratio was more difficult to interpret and, in this case, gave a less clear picture of the salinity influence.     

Distribution and abundance of littoral benthic fauna in Canadian prairie saline lakes

The littoral benthos of 18 lakes in Alberta and Saskatchewan ranging in salinity from 3 to 126 (g1^–1 TDS) were investigated twice, in the spring and in the summer of 1986. Multiple Ekman dredge samples were taken at water depths of about 0.5, 1.0 and 2 metres in each transect. Two to three transects were used in each lake according to its estimated limnological diversity for a total of 114 stations. A total of 76 species was present varying from 29–31 species in the three lakes of lowest salinity (means of 3.1–5.55) to only 2 species in lakes exceeding 100. Species richness decreased rapidly in salinities greater than 15.Biomass maximum mean of 10.91 g m^–2 dry weight (maximum 63.0 g m^–2) occurred in culturally eutrophic Humboldt Lake (3.1) but one third as great in other low salinity lakes. However, biomass again increased to about 4.5 gm^–2 in two lakes of 15 As the salinity increased still further biomass declined steadily until a minimum of 0.0212 g m^–2 was recorded in most saline Aroma Lake (mean 119). Summer biomass (11 lakes) was greater than spring biomass (4 lakes) because some groups such as amphipods, corixids and ostracods became more abundant in summer. Wet weight biomass averaged 15.8 of dry weight biomass.Seasonality (spring or summer), sediment texture and organic matter content, water depth, pH, salinity (TDS) and the presence of aquatic plants ( plant cover) were considered in the matrix involving species dry weight biomass at each of 117 stations. TWINSPAN classification of the samples yielded a dendrogram with 18 indicator species. Successive dichotomies divided these indicator species into four main lake groups based on salinity, i.e., Group I: 3–10 (Gammarus, Glyptotendipes I, Chironomus cf. plumosus), Group II: 10–38%. (Hyalella, Enallagma,Bezzia), Group III: 38–63 (Hygrotus salinarius, Cricotopus ornatus), Group IV: >63 (Dolichopodidae, Ephydra hians). Each of these main groups was subdivided into smaller groups of lakes based on factors such as pH, seasonality (spring or summer species dominance), organic matter and plant cover. Depth of samples played no apparent role.     

Carbon-13 variation with depth in soils of Brazil and climate change during the Quaternary

Paleoecological and geomorphological studies indicate that, during the middle Holocene, there was a predominance of drier conditions with grassy savannahs replacing forests across the South American continent. Modern savannahs are composed mainly of C4 plants and soils developed under this type of vegetation show enrichment in ¹³C compared to soils under C3 vegetation cover. If soils contain stabilized organic matter formed in the middle Holocene, we hypothesize that former C4 vegetation would be evidenced by a large enrichment of ¹³C in soil organic matter (SOM). We investigate this possibility examining the depth variation of carbon isotopic composition in 21 soil profiles collected by different researchers at 14 different sites in Brazil. Of these, profiles from only three sites showed a marked increase of ¹³C with depth (9–10 enrichment in ¹³C difference between the surface soil and deepest depth); two sites showed intermediate enrichment (4–5), and nine sites showed a small enrichment of approximatelly 2.5. The majority of sites showing all-C3 derived SOM were in the Amazon region. Possible causes for the absence of a large ¹³C enrichment with depth are: (1) dominance of C3 rather than C4 grasses in mid-Holocene savannahas, (2) soil profiles did not preserve organic matter derived from mid-Holocene plants, (3) the retreat of forest areas did not occur on a regional scale, but was a much more localized phenomenon.     

Trophic relationships in the nearshore zone of Martel Inlet (King George Island,Antarctica): δ<Superscript>13</Superscript>C stable-isotope analysis

Carbon isotopic composition was used to assess the linkage between three different potential sources of energy and the community in the shallow coastal zone of Martel Inlet. Stable ¹³C ratios ranged from –28.7 for the zooplankton plus phytoplankton to –14.4 for the grazer Nacella concinna. Microphytobenthos (–16.7) was considerably more enriched in ¹³C than were suspended particulate matter (SPM) (–25.6) and macroalgal fragments (–23.6 and –21.1), indicating that stable carbon isotope analysis might be used to discern the relative contribution of these sources of primary production. There is a benthic-pelagic coupling between plankton, benthic suspensivores, the ophiuroid Ophionotus victoriae and the icefish Chaenocephalus aceratus. Benthic grazers such as N. concinna, deposit feeders such as Yoldia eightsi and the nematodes showed a tight coupling with the microphytobenthos and the sediment. Some omnivorous/depositivorous polychaetes, echinoids, amphipods and the fish Notothenia coriiceps showed values close to the ratios of the macroalgal fragments. Benthic carnivores and/or scavengers were generally enriched over suspensivores and depleted in relation to microphytobenthos grazers, showing a considerable overlap in ¹³C values throughout the food web, without any clear coupling with the primary sources of organic matter. The trophic web in the shallow zone of high benthic production and under seasonal ice cover in the Antarctic is more complex than it is in shelf areas, where SPM is the main food source. The soft-bottom community in the shallow zone of Martel Inlet is enriched in ¹³C due to the significant input of carbon from the microphytobenthos and macroalgal fragments.     

A bloom of Dunaliella parva in the Dead Sea in 1992: biological and biogeochemical aspects

A bloom of the unicellular green alga Dunaliella parva (up to 15 000 cells m1^–1) developed in the upper 5 m of the water column of the Dead Sea in May-June 1992. This was the first mass development of Dunaliella observed in the lake since 1980, when another bloom was reported (up to 8800 cells m1^–1). For a bloom of Dunaliella to develop in the Dead Sea, two conditions must be fulfilled: the salinity of the upper water layers must become sufficiently low as a result of dilution with rain floods, and phosphate must be available. During the period 1983–1991 the lake was holomictic, hardly any dilution with rainwater occurred, and no Dunaliella cells were observed. Heavy rain floods in the winter of 1991–1992 caused a new stratification, in which the upper 5 m of the water column became diluted to about 70% of their former salinity. Measurements of the isotopic composition of inorganic carbon in the upper water layer during the bloom (¹³C = 5.1) indicate a strong fractionation when compared with the estimated –3.4 prior to the bloom. The particulate organic carbon formed was highly enriched in light carbon isotopes ( ¹³ C = – 13.5). The algal bloom rapidly declined during the months June–July, probably as a result of the formation of resting stages, which sank to the bloom. A smaller secondary bloom (up to 1850 cells m1–1) developed between 6 and 10 m depth at the end of the summer. Salinity values at this deep chlorophyll maximum were much beyond those conductive for the growth of Dunaliella, and the factors responsible for the development of this bloom are still unclear.     

Autotrophic carbon sources for heterotrophic bacterioplankton in a floodplain lake of central Amazon

The relative contribution of autotrophic carbon sources (aquatic macrophytes, flooded forest, phytoplankton) for heterotrophic bacterioplankton was evaluated in a floodplain lake of the Central Amazon. Stable carbon isotopes (¹³C) were used as tracers. Values of ¹³C of different autotrophic sources were compared to those of dissolved organic carbon (DOC) and those of bacterially produced CO₂.The percentage of carbon derived from C₄ macrophytes for bacterially produced CO₂ was the highest, on average 89%. The average ¹³C value of CO₂ from bacterial respiration was –18.5 ± 3.3. Considering a fractionation of CO₂ of 3 by bacterial respiration, ¹³C value was –15.5, near C₄ macrophyte ¹³C value (–13.1).The average value of total DOC ¹³C was –26.8 ± 2.4. The percentage of C₄ macrophytes carbon for total DOC was on average 17%. Considering that bacteria consume mainly carbon from macrophytes, the dominance of C₃ plants for total DOC probably reflects a faster consumption of the former source, rather than a major contribution of the latter source.Heterotrophic bacterioplankton in the floodplain may be an important link in the aquatic food web, transferring the carbon from C₄ macrophytes to the consumers.     

Life cycles of marine nematodes

Summary Monhystera denticulata Timm, a free-living nematode present in the aufwuchs assemblages of several marine macrophytes located in North Sea Harbor, Southampton, New York, was isolated from Zostera marina and established in laboratory culture in order to study the influences of temperature and salinity on its life history. Under experimental conditions, M. denticulata has a generation time (Measured as the time elapsing between the first egg depositions of consecutive generations) of 10–12 days at 25° C and 26 S, which represent optimal growth conditions in the laboratory. The organism has a generation time of 20 days at 25° C and 13, 17 days at 25° C and 39, 18 days at 15° C and 26, 36 days at 15° C and 13 and 34 days at 15° C and 39. As conditions vary from the optimum of 25° C and 26 S, a decrease in temperature of 10° C and an increase or decrease in salinity of 13 results in a doubling of the generation time. At 5° C the generation time is about 180–197 days.Assuming optimum conditions and average generation time, about 15 generations of M. denticulata could occur in North Sea Harbor during the year. The number of generations occurring in reality is probably less, however, due to the fact that the females deposit their eggs over a period of several days.This work was supported by National Science Foundation Grant GB-19245.Contribution No. 04 from the Institute of Oceanography, City University of New York.     

Phytoplankton distribution in relation to sea ice,hydrography and nutrients in the northwestern Weddell Sea in early spring 1988 during EPOS

Summary Phytoplankton biomass and distribution of major phytoplankton groups were investigated in relation to sea ice conditions, hydrography and nutrients along three north-south transects in the north western Weddell Sea in early spring 1988 during the EPOS Study (European Polarstern Study), Leg 1. Three different zones along the transects could be distinguished: 1) the Open Water Zone (OWZ) from 58° to 60°S with high chlorophyll a concentrations up to 3.5 g l^–1; 2) the Marginal Ice Zone (MIZ) from 60° to about 62.5° with chlorophyll a concentrations between 0.1 and 0.3 g l^–1, and 3) the closed pack-ice zone (CPI) from 62.5° to 63.2°S with chlorophyll a concentrations below 0.1 gl^–1. Nutrient concentrations increased towards the south showing winter values under the closed pack-ice. Centric diatoms such as Thalassiosira gravida and Chaetoceros neglectum forming large colonies dominated the phytoplankton assemblage in terms of biomass in open water together with large, long chain forming, pennate diatoms, whereas small pennate diatoms such as Nitzschia spp., and nanoflagellates prevailed in ice covered areas. Fairly low concentrations of phytoplankton cells were encountered at the southernmost stations and many empty diatom frustules were found in the samples. The enhanced phytoplankton biomass in the Weddell-Scotia-Confluence area is achieved through sea ice melting in the frontal zone of two different water masses, the Weddell and the Scotia Sea surface waters.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Stable carbon isotope ratios for the gray whale (<Emphasis Type="Italic">Eschrichtius robustus</Emphasis>) in the breeding grounds of Baja California Sur,Mexico

This work investigated the feeding ecology and behaviour of gray whales in Bahía Magdalena. Underwater observations of bottom feeding were made (n=4). Skin biopsies of the gray whale had a carbon isotope value of –16.5 ± 0.1 (range from –16.4 to –16.7, n=7). Prey in Bahía Magdalena had a carbon isotope value of –18.4. Dietary enrichment from prey in Bahía Magdalena would correspond to 2 ± 0.1, whereas previously published results for prey in Alaska would result in an enrichment of 3, which suggests that whales were more likely feeding on prey from Bahía Magdalena. Carbon isotopic oscillation along the baleen plate of a stranded 1-year-old whale showed a variation in diet during the year, which suggests continual feeding during this time and corresponding to dietary sample measurements from Bahía Magdalena in winter and Alaska in summer.     

Stable isotope and radiocarbon compositions of methane emitted from tropical rice paddies and swamps in Southern Thailand

Stable isotopes (¹³C, D) and radiocarbon weremeasured in methane bubbles emitted from rice paddies and swamps in southernThailand. Methane emitted from the Thai rice paddies was enriched in¹³C (mean ¹³C; –51.5 ±7.1 and–56.5 ± 4.6 for mineral soil and peat soil paddies,respectively)relative to the reported mean value of methane from temperate rice paddies(– 63 ± 5). Large seasonal variation was observed in¹³C(32) in the rice paddies, whereas variationinD was much more smaller (20), indicating that variation in¹³C is due mainly to changes in methane production pathways.Values of ¹³C were lower in swamps (–66.1 ±5.1)than in rice paddies. The calculated contribution of acetate fermentation from¹³C value was greater in rice paddies (mineral soils:62–81%, peat soils: 57–73%) than in swamps (27–42%). Din methane from Thai rice paddies (–324± 7 (n=46)) isrelativelyhigher than those from 14 stations in Japanese rice paddies ranging from–362 ± 5 (Mito: n=2) to –322 ± 8(Okinawa: n=3), due tohigher D in floodwaters. ¹⁴C content in methane produced fromThai rice paddies (127±1 pMC) show higher ¹⁴Cactivity compared with previous work in paddy fields and those from Thai swamps(110±2 pMC).     

A global survey of carbon isotope discrimination in plants from high altitude

Summary Carbon 13/12 isotope ratios have been determined from leaves of a hundred C₃ plant species (or ecotypes) from all major mountain ranges of the globe, avoiding drought stressed areas. A general increase in ¹³C content was found with increasing altitude, i.e. overall discrimination against the heavy isotope is reduced at high elevation. The steepest decline of discrimination is observed in taxa typically ranging to highest elevations (e.g. the genus Ranunculus). Mean ¹³C for all samples collected between 2500 and 5600 m altitude is-26.15 compared to the lowland average of-28.80 (P<0.001). Forbs from highest elevations reach-24. According to theory of ¹³C discrimination this indicates decreasing relative limitation of carbon uptake by carboxylation. In other words, we estimate that the ratio of internal to external partial pressure of CO₂ (p _i /p _a )in leaves of high elevation plants is lower than in leaves of low altitude. These results confirm recent gas exchange analyses in high and low elevation plants.     

Diversity,metabolic types and δ13C carbon isotope ratios in the grass flora of Namibia in relation to growth form,precipitation and habitat conditions

The grass flora of Namibia (374 species in 110 genera) shows surprisingly little variation in ¹³C values along a rainfall gradient (50–600 mm) and in different habitat conditions. However, there are significant differences in the ¹³C values between the metabolic types of the C4 photosynthetic pathway. NADP-ME-type C4 species exhibit the highest ¹³C values (–11.7 ) and occur mainly in regions with high rainfall. NAD-ME-type C4 species have significantly lower ¹³C values (–13.4 ) and dominate in the most arid part of the precipitation regime. PCK-type C4 species play an intermediate role (–12.5 ) and reach a maximum abundance in areas of intermediate precipitation. This pattern is also evident in genera containing species of different metabolic types. Within the same genus NAD species reach more negative ¹³C values than PCK species and ¹³C values decreased with rainfall. Also in Aristida, with NADP-ME-type photosynthesis, ¹³C values decreased from –11 in the inland region (600 mm precipitation) to –15 near the coast (150 mm precipitation), which is a change in discrimination which is otherwise associated by a change in metabolism. The exceptional C3 species Eragrostis walteri and Panicum heterostachyum are coastal species experiencing 50 mm precipitation only. Many of the rare species and monotypic genera grow in moist habitats rather than in the desert, and they are not different in their carbon isotope ratios from the more common flora. The role of species diversity with respect to habitat occupation and carbon metabolism is discussed.     

Experimental effects of elevated salinity on three benthic invertebrates in Pyramid Lake,Nevada

Salinity of Pyramid Lake increased from 3.7 to 5.5 between 1933 and 1980. Concern over future reductions in overall species richness prompted experiments to assess responses of dominant lake organisms to elevated salinity. Salinity tolerances of three important benthic invertebrates, Hyalella aztecta, Chironomus utahensis, and Heterocypris sp., were tested in controlled laboratory bioassays and also in a semi-natural environment consisting of large (47 m³) mesocosms.Densities of H. azteca in mesocosms were significantly lower at salinities of 8.0 and 11.0 compared with 5.6 controls in year one, but not in 8.5 salinity mesocosms in year two. The 96-h LC₅₀ for H. azteca was high at 19.5. Short-term mortalities of C. utahensis were 100% at salinities of 13.3 and greater. Fifty-seven percent fewer larvae matured from third to fourth instar at 8.9 than at 5.5 salinity in 17 day subacute bioassays. Furthermore, larval chironomid densities and emergence of adults from mesocosms were significantly reduced at salinities of 8.0 and higher compared with controls. Mortality of Heterocypris sp. was 50% at a salinity of 18.6 in laboratory bioassays and populations in mesocosms ranged between 40 and 100% lower at salinities of 8.0 and 11.0 than in controls.Multiple generation mesocosm experiments indicated all three invertebrates were more sensitive to elevated salinity than results of short-term bioassays. Our studies suggest populations of these invertebrates may be reduced from present levels if Pyramid Lake's salinity were to double, although none are expected to be extirpated. Food habit shifts and reduced production of lake fishes are likely consequences of salinity-induced disruption in the benthic invertebrate forage base.     

Summer distribution of netphytoplankton in the Atlantic sector of the Southern Ocean

The surface distribution of netphytoplankton (>20 m) in the Atlantic sector of the Southern Ocean was investigated along two transects during early and late austral summer 1990/91. Sampling was under-taken at intervals of 60 of latitude between 34° and 70°S for the analysis of nutrients and for the identification and enumeration of netphytoplankton. Peaks in total diatom abundances were recorded at the Antarctic Polar Front (APF), in the vicinity of the South Sand wich Islands, in the marginal ice zone and in the neritic waters of the Atlantic sector of Antarctica. Cluster analysis indicates the existence of two major zones between Southern Africa and Antarctica. Diatom abundance increased south of the Antarctic Polar From along both transects, which can be partially explained by gradients of silicate concentration. Small chain-forming species (e.g. Fragilariopsis kerguelensis and Nitzschia lineata) dominated the diatom assemblages in early summer, while larger species, such as Rhizosolenia hebetata f. semispina and Corethron criophilum, dominated late summer diatom assemblages. The predominance of typically ice-associated forms in early summer suggests that the release of epontic cells during ice melt provides the initial inoculum for the netphytoplankton biomass. These small diatoms are subsequently replaced by larger species.