Respiration rates of Chiloplacus sp. and other arctic nematodes at low and high temperatures

Summary Respiration of an undescribed species of soil nematode of the genus Chiloplacus from the Canadian High Arctic was measured at 2°, 5°, 10°, 15°, 20° and 25°C. The corresponding metabolic rates were 0.2697×10^-3 l, 0.3406×10^-3 l, 0.8408×10^-3 l, 0.8539×10^-3 l, 1.8420×10^-3 l and 2.9360×10^-3 l O₂ ind^-1 h^-1, respectively, for a nematode of 1.0 g dry weight. The relationship between respiration and dry weight for Chiloplacus sp. at 10°C is described by the function log R=-3.0693+0.8844 log W. Q₁₀ values for the 2°–5°, 5°–10°, 10°–15°, 15°–20° and 20°–25°C temperature intervals were 2.18, 6.09, 1.03, 4.65 and 2.54, respectively. Chiloplacus sp. showed raised metabolic rates at low tempetatures compared with species from warmer environments. Metabolic rates of representative samples of the soil, nematode fauna (dominated by individuals of the genus Plectus) from the same location were 0.1593×10^-3 l, 0.3603×10^-3 l and 0.5332×10^-3 l O₂ ind^-1 h^-1 at 5°, 10° and 15°C for an average nematode of 0.4297 g dry weight.     

Ventilation rate and behavioural responses of two species of intertidal goby (Pisces: Gobiidae) at extremes of environmental temperature

We investigated the behavioural responses of two gobiid fish species to temperature to determine if differences in behaviour and ventilation rate might explain any apparent vertical zonation. A survey of the shore at Manly, Moreton Bay revealed Favonigobius exquisitus to dominate the lower shore and Pseudogobius sp.4 the upper shore. These species were exposed to a range of temperatures (15–40°C) in aquaria for up to 6 h. At 20 °C F. exquisitus exhibited a mean gill ventilation rate of 26 ± 1.4 bpm (beats per minute) differing significantly from Pseudogobius, which ventilated at a fivefold greater rate of 143 ± 6 bpm. The ventilation rate in F. exquisitus underwent a fivefold increase from normal local water temperature (20 °C) to high temperature (35 °C) conditions, whereas that of Pseudogobius did not even double, suggesting that Pseudogobius sp. is a better thermal regulator than F. exquisitus.While both species emerged from the water at high temperatures (>30 °C) the behaviours they exhibited while immersed at high temperature were quite different. F. exquisitus undertook vertical displacement movements we interpret as an avoidance response, whereas Pseudogobius sp. appeared to use a coping strategy involving movements that might renew the water mass adjacent to its body. The thermal tolerances and behaviours of F. exquisitus and Pseudogobius sp. are in broad agreement with their vertical distribution on the shore.     

The combined relationship of temperature and molybdenum concentration to nitrogen fixation byAnabaena cylindrica

The joint effects of growth temperature, incubation temperature, and molybdenum concentration on the nitrogen fixation rate ofAnabaena cylindrica were determined using the acetylene-reduction technique. The nitrogen-fixation response to increased molybdenum concentration varied among three growth temperatures (15°, 23°, and 30° C). The pattern of rate change was similar within a growth temperature but increased overall in magnitude with the three incubation temperatures (also 15°, 23°, and 30° C). The maximum rate of nitrogen fixation occurred at 30°C regardless of previous growth temperature. The minimum molybdenum concentration necessary to yield substantial acetylene reduction varied with growth temperature: at 15°C, 15g 1^–1 was effective; at 23°C, less than 5g 1^–1 was effective; and at 30°C, 50g 1^–1 was effective. At all three growth temperatures, increases in molybdenum concentration above the minimum effective concentration produced increases in acetylene reduction. However, at higher molybdenum concentrations inhibition of nitrogen fixation occurred.     

Biology and temperature relationships of Chrysopa sp., Micromus tasmaniae and Nabis capsiformis

Immature Chrysopa sp. and Nabis capsiformis required 335 and 325 d°, respectively, for development from egg to adult, while larvae of Micromus tasmaniae were able to complete development at 5°. Mean adult female longevity and oviposition rate at 23° were 52 d (max. 83 d) and 18.1 eggs/d, and 30 d (max. 43 d) and 10.4 eggs/d for C. sp. and N. capsiformis respectively, and oviposition rate of M. tasmaniae averaged 19.1 eggs/d during 5 weeks. Reduced longevity and increased oviposition rate at higher temperatures were accounted for by basing adult biology on physiological time above the immature developmental thresholds. Intrinsic rates of increase were thus calculated as 9.820, 6.868, and 8.366 eggs/10³ d° above thresholds of 10.5°, -2.9°, and 11.3° for C. sp., M. tasmaniae, and N. capsiformis, respectively.

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Résumé L'examen a porté sur l'influence de différentes températures constantes sur le développement et la biologie imaginale de trois espèces prédatrices (Chrysopa sp., peut-être C. signata, Micromus tasmaniae et Nabis capsiformis) récoltées dans des champs de coton du sud-est du Queensland en Australie. C. sp. et N. capsiformis ont besoin respectivement de 335° au dessus d'un seuil de 10.5° et de 325° au dessus d'un seuil de 11.3°, pour se développer de l'oeuf à l'adulte. Les larves de M. tasmaniae pouvant effectuer la totalité de leur dévelopment a 5°.-A 23° les longévités des femelles adultes et les taux de ponte de C. sp. et N. capsiformis sout en moyenne de 52 j. (maximum 83) et 30 j. (maximum 43) d'une part et 18.1 et 10.4 ufs par jour d'autre part. Le taux de ponte de M. tasmaniae est de 19,1 ufs par jour pendant 5 semaines à 23°. La longévité réduite et le taux de ponte accru aux températures supérieures sont interprétés en basant la biologie imaginale sur le temps physiologique au dessus des seuils de développement.Les taux d'accroissement intrinsèque (r_m) sont plus élevés aux températures élevées, principalement à la suite du taux de développement accru. M. tasmaniae possède le r_m le plus élevé à toutes les températures par suite d'un développement rapide et de seuils thermiques bas, d'une brève période précédant la ponte et d'une date de ponte maximum précoce. Le r_m de C. sp. est plus élevé que celui de N. capsiformis à la suite de son taux de ponte plus élevé.Les valeurs de r_m fixées à partir du temps physiologique sont respectivement: 9,820, 6.868 et 8,366 ufs femelles/10³ d° au dessus des seuils de 10,5°, -2,9° et 11,3° pour C. sp., M. tasmaniae et N. capsiformis.

     

Effects of Temperature and Turbulence on the Predator–Prey Interactions between a Heterotrophic Flagellate and a Marine Bacterium

Biotic and abiotic factors can influence interactions between microbial grazers and their prey, thus impacting both the cycling of biogenic carbon within the surface layer of the ocean and the export of carbon to the deep ocean and higher trophic levels. In this study, microcosm experiments were used to evaluate the combined effect of temperature and turbulence on the growth rate of a marine bacterium (Vibrio splendidus), a protistan predator (Paraphysomonas sp.), and the community grazing impact of Paraphysomonas sp. on V. splendidus. It was found that the artificial turbulence generated (1.35 × 10⁻¹ cm² s⁻³) significantly increased the rates of growth of Paraphysomonas sp. at high (>10°C), but not low (<5°C) temperatures, and that turbulence had no effect on the growth of V. splendidus. Both flagellate and bacterial growth were temperature dependent and decreased 4- to 6-fold as temperatures decreased from 15 to 0°C. Bacterial grazing mortality by Paraphysomonas sp. was 1.3- to 2.5-fold greater in the turbulent than static treatments among all four temperatures, and the rates of cell-specific ingestion of bacteria by Paraphysomonas sp. was 2-fold greater at 15 and 10°C in the turbulent than in the static treatment. Hence, this study shows that turbulence can influence nanoflagellate grazing at temperatures >5°C and suggests that at low temperatures, increased viscosity may limit the size of organisms that can be affected by small-scale turbulence.Present address (M.P. Delaney): Goddard Earth Sciences & Technology Center, NASA Goddard Space Flight Center, Mail Code 900.1, Greenbelt, MD 20771     

Cold-active DnaK of an Antarctic psychrotroph Shewanella sp. Ac10 supporting the growth of dnaK-null mutant of Escherichia coli at cold temperatures

Shewanella sp. Ac10 is a psychrotrophic bacterium isolated from the Antarctica that actively grows at such low temperatures as 0°C. Immunoblot analyses showed that a heat-shock protein DnaK is inducibly formed by the bacterium at 24°C, which is much lower than the temperatures causing heat shock in mesophiles such as Escherichia coli. We found that the Shewanella DnaK (SheDnaK) shows much higher ATPase activity at low temperatures than the DnaK of E. coli (EcoDnaK): a characteristic of a cold-active enzyme. The recombinant SheDnaK gene supported neither the growth of a dnaK-null mutant of E. coli at 43°C nor phage propagation at an even lower temperature, 30°C. However, the recombinant SheDnaK gene enabled the E. coli mutant to grow at 15°C. This is the first report of a DnaK supporting the growth of a dnaK-null mutant at low temperatures.     

Growth,growth efficiency,and assimilation efficiency of the Tahoe sucker in cyclic and constant temperature

Synopsis Tahoe sucker, Catostomus tahoensis, were fed at three ration levels (starvation, 50% of repletion, and repletion) at three constant and cyclic temperature regimes (4–12°, 8°, 8–18°, 13°, and 13°–23°, 18° C) to examine growth rate and gross growth efficiencies. Growth rates increased with increasing temperature and ration level. Growth rates were not different between cyclic temperatures and the constant temperature equivalent to the mean of the cycle. Growth efficiencies were similar for cyclic and constant temperature regimes. Maintenance rations increased from 0.9% of the initial wet weight per day at low temperatures to 2.0 and 1.7% at intermediate and high temperatures, respectively. Assimilation efficiencies (not measured at low temperatures) did not differ between constant and cyclic temperatures. Tahoe sucker growth rates and assimilation efficiencies may not be enhanced in small streams because of this species' inability to mediate temperature cycles through behavioral thermoregulation.     

Biology, life table and host specificity of the mushroom pest, Brennandania lambi (Acari: Pygmephoroidea)

Biology and life table parameters of Brennandania lambi (Krczal) were studied at different temperatures while feeding on white mushroom (Agaricus bisporus) mycelium cultured on mushroom compost. The duration of egg and larva development, preoviposition and oviposition period, female longevity, and the time to 50% mortality declined as temperature increased from 16 to 28°C. The threshold temperature of development (female) was 9°C and the thermal constant for completion of development (female) was 195 day-degrees. At 16, 20, 24 and 28°C, the total fecundity (eggs/female) was 71, 67, 66 and 57, respectively and the daily fecundity rate (eggs/female/day) was 5.6, 8.7, 8.7 and 9.1, respectively. The sex ratio (female/male) ranged from 1.9 to 2.1 at 16–28°C. At 16, 20, 24 and 28°C, the intrinsic rate of natural increase (r _m) was 0.11, 0.18, 0.22 and 0.27, respectively, and the population doubling time was 6.1, 3.9, 3.2 and 2.5 days, respectively. All life stages of the mite died when exposed to 35°C constant temperature for 24h, or to 32°C constant temperature for 12 days or to 31–35°C (average 32.9°C) ambient temperature for 4 days. Brennandania lambi completed development only when fed on Ag. bisporus mycelium growing on mushroom compost. It could not survive on mushroom mycelia of Auricularia auricula, Au. polytricha, Ganoderma lucidum, Hericium erinaceus, Lentinus edodes, Pleurotus ostreatus, P. sajor-caju and Tremella fuciformis.     

Thermal properties of NADP:ferredoxin oxidoreductase and ferredoxin isolated from a thermophilic blue-green alga

NADP:ferredoxin oxidoreductase (EC. 1.6.7.1.) isolated from a thermophilic blue-green alga, Synechococcus sp., was stable at temperatures up to 65°C. The diaphorase and cytochrome c reductase activities of the enzyme were low at 25°C but increased with elevated temperature to reach a maximum at about 60°C. The pH-profile of the diaphorase activity showed a peak at pH 9.0 at 55°C, whereas the activity was largely independent of pH at 25°C. High concentrations of NaCl suppressed activity at both high and low temperatures. In the cytochrome c reductase activity catalyzed by the enzyme, ferredoxin served as an electron carrier in a temperature-insensitive manner over a wide range of temperature. The results support the view that the optimum and the upper limiting temperatures for photosynthesis in this alga are related to thermal properties of proteins.     

Combined Effects of Algal (<Emphasis Type="Italic">Chlorella vulgaris</Emphasis>) Food Level and Temperature on the Demography of <Emphasis Type="Italic">Brachionus havanaensis</Emphasis> (Rotifera): a Life Table Study

We evaluated the combined effects of food (0.5 × 10⁶, 1.0 × 10⁶ and 2.0 × 10⁶ cells ml⁻¹ of Chlorella vulgaris) and temperature (15, 20 and 25 °C) on life history variables of B. havanaensis. Regardless of Chlorella density there was a steep fall in the survivorship of B. havanaensis at 25 °C. Both food level and temperature affected the fecundity of B. havanaensis. At any given food level, rotifers cultured at 15 °C showed extended but low offspring production. At 25 °C, offspring production was elevated, the duration of egg laying reduced and the fecundity was higher during the latter part of the reproductive period. The effect of food level was generally additive, at any given temperature, and higher densities of Chlorella resulted in higher offspring production. Average lifespan, life expectancy at birth and generation time were 2–3 times longer at 15 °C than at 25 °C. At 20 °C, these remained at intermediate levels. The shortest generation time (about 4 days) was observed at 25 °C. Gross and net reproductive rates and the rate of population increase (r) increased with increasing temperature and generally, at any given temperature, higher algal food levels contributed to higher values in these variables. The r varied from 0.11 to 0.66. The survival patterns and lower rates of reproduction at 15 °C suggest that the winter temperatures (10–15 °C) prevailing in many waterbodies in Mexico City allow this species to sustain throughout the year under natural conditions.     

Distribution of benthic algae and macroinvertebrates along a thermal stream gradient

The distribution and abundance of benthic algae and macroinvertebrates were examined along a natural thermal gradient formed by hot springs in Little Geysers Creek, Sonoma Co., California, USA. Maximum water temperatures ranged from 52 °C at the uppermost station to 23 °C at a station 400 m downstream. Benthic chlorophyll a decreased exponentially from 2.5 g m^–2 at 52 °C to less than 0.1 g m^–2 at 23 °C, a pattern of decline also exhibited by algal phaeophytin. Blue-green algae dominated at higher temperatures but were replaced by filamentous green algae and diatoms at lower temperatures.Macroinvertebrates were absent at temperatures 45 °C; the highest density (> 150 000 m^–2, mainly Chironomidae) occurred at 34 °C, whereas biomass was highest (4.6 g m^–2, as dry weight) at 23 °C and species richness (15 species) was highest at 27 °C. The two predominant macroinvertebrate populations (the midge Tanytarsus sp. and the caddisfly Helicopsyche borealis) occurred at sites that were several degrees below their lethal thermal threshold, suggesting that a temperature buffer is maintained.     

Spray drying of the dehalogenating bacterium Rhodococcus sp.

The bacteria Rhodococcus sp. and Xanthobacter autotrophicus have the ability to dehalogenate a broad range of halogenated hydrocarbons. The applicability of spray drying to the preservation of the microorganisms and the intracellular enzyme halidohydrolase (E.C.3.8.1.1) was examined. K₂SO₄, MgSO₄, glutamate and sucrose were added as stabilizers and carriers. Spray drying was carried out at inlet air temperatures of 100–120 °C and outlet air temperatures of 65–72 °C. Best results were obtained by the addition of 5% K₂SO₄ and at 107 °C air inlet temperature. Dried preparations of Rhodococcus sp. exhibited a crystalline consistency and a 95% recovery of cellular activity. After storage at 4 °C for six months the enzyme preparation showed no loss in activity. Spray dried preparations of Xanthobacter autotrophicus showed only a 4% recovery of cellular activity.List of Symbols MSG Monosodiumglutamate - RC % Recovery of stabilizer and biomass - RCA % Recovery of cellular activity ([U/g biomass after the spraydrying]/[U/g biomass of untreated cells]) 100 - RCB % Recovery of biomass - SR % Survival rate - T ₁ °C Inlet air temperature - T ₂ °C Exit air temperature - W % Water content - Y.Akt % Yield in enzyme activity This work was supported by the Jubiläumsfond der Oesterreichischen Nationalbank, Projekt No. 4499.     

Effect of acute pH depression on the survival of the freshwater amphipod Hyalella azteca at variable temperatures: field and laboratory studies

Field observations on temperature and pH of a small pond showed that a amphipod population of Hyalella azteca was exposed to variable seasonal pH between 5.10–5.85, and water temperatures between 2–21 °C. Laboratory experiments were designed to simulate seasonal temperatures and field pHs of a small pond habitat. Laboratory bioassay experiments were conducted to determine the survival of Hyalella azteca at pHs 4, 5, 6 and 7, and varying temperatures of 5°, 10°, 15°, 20° and 25 °C.The LT₁₀₀ at pH 4 and 25 °C was 5.7 ± 0.47 days, compared to 47.3 ± 2.49 days at 5 °C. An Analysis of Variance (ANOVA) showed temperature was a significant (p > 0.0001) source of variation in the acute lethality of pH to H. azteca. A Duncans Multiple Range Test (DMRT) further showed that in laboratory experiments at pH 4, there was a significant difference ( = 0.01) between the LT_100s at 5°, 10°, 15° and 20 °C, but not between temperatures 20° and 25 °C.     

Kinetics of dormancy release and the high temperature germination response in Aesculus hippocastanum seeds

The kinetics of primary dormancy loss were investigated in seeds of horse chestnut (Aesculus hippocastanum L.) harvested in four different years. Freshly collected seeds from 1991 held for up to 1 year at temperatures between 2C and 42C exhibited two peaks in germination (radicle growth), representing a low temperature (2-8°C) and a high temperature response (31-36°C). Germination at 36°C generally occurred within 1 month of sowing, but was never fully expressed in the seedlots investigated. At low temperatures (2-8°C), germination started after around 4 months. Generally, very low levels of termination were observed at intermediate temperatures (11-26°C). Stratification at 6°C prior to germination at warmer temperatures increased the proportion of seeds that germinated, and the rate of germination for all seedlots. Within a harvest, germination percentage (on a probit scale) increased linearly with stratification time and this relationship was independent of germination temperature (16-26°C). However, inter-seasonal differences in the increases in germination capacity following chilling were observed, varying from 0.044 to 0.07 probits d^-1 of chilling at 6°C. Increased sensitivity to chilling was associated with warmer temperatures during the period of seed filling. The estimated base temperature for germination, Tb, for newly harvested seeds varied slightly between collection years but was close to 25°C. For all seedlots, Tb decreased by 1°C every 6 d of chilling at 6°C. This systematic reduction in Tb with chilling ultimately facilitated germination at 6°C after dormancy release.     

The removal of a heated water discharge from a lake and the effect upon an epiphytic algal community

The effects of the removal of a heated water discharge from Lake Wabamun, Alberta (longitudes 114°26 and 114°44W; latitudes 53°30 and 53°35N) upon epiphytic algae has been documented. Due to the timing of the cessation of flow the first year without elevated temperatures was one of transition. Standing crops returned to normal lake levels the following year. Species composition changes occurred, and species such as Epithemia turgida, Amphipleura pellucida, Nitzschia fonticola, Rhopalodia gibba, Rivularia haematites, and Scytonema alatum, all of which were detrimentally affected by the elevated temperatures, returned to the previously affected area, while species such as Oedogonium sp., Spirogyra sp. and Cladophora glomerata, dominant at times in the heated area, diminished in importance. The ability of Cocconeis placentula to grow at low light intensities (15–110 µEinsteins m^–2 s^–1) was again demonstrated.     

Reduction of metabolic rate and thermoregulation during daily torpor

Physiological mechanisms causing reduction of metabolic rate during torpor in heterothermic endotherms are controversial. The original view that metabolic rate is reduced below the basal metabolic rate because the lowered body temperature reduces tissue metabolism has been challenged by a recent hypothesis which claims that metabolic rate during torpor is actively downregulated and is a function of the differential between body temperature and ambient temperature, rather than body temperature per se. In the present study, both the steady-state metabolic rate and body temperature of torpid stripe-faced dunnarts, Sminthopsis macroura (Dasyuridae: Marsupialia), showed two clearly different phases in response to change of air temperature. At air temperatures between 14 and 30°C, metabolic rate and body temperature decreased with air temperature, and metabolic rate showed an exponential relationship with body temperature (r ²=0.74). The Q ₁₀ for metabolic rate was between 2 and 3 over the body temperature range of 16 to 32°C. The difference between body temperature and air temperature over this temperature range did not change significantly, and the metabolic rate was not related to the difference between body temperature and air temperature (P=0.35). However, the apparent conductance decreased with air temperature. At air temperatures below 14°C, metabolic rate increased linearly with the decrease of air temperature (r ²=0.58) and body temperature was maintained above 16°C, largely independent of air temperature. Over this air temperature range, metabolic rate was positively correlated with the difference between body temperature and air temperature (r ²=0.61). Nevertheless, the Q ₁₀ for metabolic rate between normothermic and torpid thermoregulating animals at the same air temperature was also in the range of 2–3. These results suggest that over the air temperature range in which body temperature of S. macroura was not metabolically defended, metabolic rate during daily torpor was largely a function of body temperature. At air temperatures below 14°C, at which the torpid animals showed an increase of metabolic rate to regulate body temperature, the negative relationship between metabolic rate and air temperature was a function of the differential between body temperature and air temperature as during normothermia. However, even in thermoregulating animals, the reduction of metabolic rate from normothermia to torpor at a given air temperature can also be explained by temperature effects.Abbreviations BM body mass - BMR basal metabolic rate - C apparent conductance - MR metabolic rate - RMR resting metabolic rate - RQ respiratory quotient - T _a air temperature - T _b body temperature - T _lc lower critical temperature - T _tc critical air temperature during torpor - TMR metabolic rate during torpor - TNZ thermoneutral zone - T difference between body temperature and air temperature - VO₂ rate of oxygen consumption     

Respiratory studies on two small freshwater amoebae

The changes in respiration rate and mean cell volume induced by temperature within the range 10°C–25°C were investigated in two small species of freshwater amoebae,Saccamoeba limax Page andVannella sp. Mean cell volume varied in response to temperature, with maxima at 20°C inVannella sp. (10.15× 10³ (±1.80)m³ and 15°C inS. limax (9.08×10³ (±0.93)m³. Respiration rate increased over the temperature range investigated. The highest rates and the greatest rate of increase between temperatures occurred inVannella sp. Q₁₀ ranged between 0.12 and 1.33 inS. limax and between 1.77 and 7.36 inVannella sp. A regression of log oxygen uptake versus log cell volume incorporating the data of the present investigation and the data of other workers on amoeba respiration is presented, and the ecological significance and application of such data discussed.     

Effect of temperature on the growth,total lipid content and fatty acid composition of recently isolated tropical microalgae Isochrysis sp., Nitzschia closterium,Nitzschia paleacea,and commercial species Isochrysis sp. (clone T.ISO)

The effect of temperature from 10 °C to 35 °C on the growth, total lipid content, and fatty acid composition of three species of tropical marine microalgae, Isochrysis sp., Nitzschia closterium, N. paleacea (formerly frustulum), and the Tahitian Isochrysis sp. (T.ISO), was investigated.Cultures of N. closterium, Isochrysis sp. and T.ISO grew very slowly at 35 °C, while N. closterium did not grow at temperatures higher than 30 °C or lower than 20 °C. N. paleacea was low-temperature tolerant, with cells growing slowly at 10 °C. N. paleacea produced the highest percentage of lipids at 10 °C, while the other species produced maximum amounts of lipid at 20 °C. None of the species maintained high levels of polyunsaturated fatty acids (PUFAs) at high growth temperature and there was a significant inverse relationship between the percentage of PUFAs and temperature for N. paleacea. A curved relationship was found between temperature and percentage of PUFA for N. closterium and tropical Isochrysis sp., with the maximum production of PUFA at 25 °C and 20 °C, respectively. The two Nitzschia species produced higher levels of the essential fatty acid eicosapentaenoic acid [20:5(n-3)] at lower growth temperatures, but the two Isochrysis species had little change in percentage of 20:5(n-3) with temperature. Only T.ISO had the highest percentage of 22:6(n-3) at lowest growth temperature (11.4% total fatty acids at 10 °C).School of Mathematical and Physical SciencesAuthor for correspondence     

Effect of high temperatures on seed germination of two woody Leguminosae

Cytisus scoparius and Genista florida regenerate after fire by stump-sprouting but also by seed. Seeds of these species were heated to a range of temperatures similar to those registered on the surface soil during natural fires (from 50 to 150 °C) and a range of exposure times (from 1 to 15 min). No germination was observed at high temperatures, 130 °C, when the exposure time was 5 min or more. However, moderate heat treatments (at 70 and 100 °C) significantly increased the rate of germination relative to controls. Cytisus scoparius is more favoured by fire action than Genista florida, with germination rates slightly greater following 100 °C for 5 min and 130 °C for 1 min than after mechanical scarification.     

Light-temperature interactions on the growth of Antarctic diatoms

Summary The combined effect of various temperatures and light intensities on the growth of seven species of antarctic diatoms in culture has been studied. With the exception of Chaetoceros deflandrei whose thermal tolerance is fairly good, these obligatory psychrophils cannot survive in temperatures above 6° to 9° C. Their mean growth rate is relatively low, between 0.24 div d^–1 for Corethron criophilum and 0.63 div d^–1 for C. deflandrei. Regardless of light intensity, growth rate increased with the temperature to reach a maximum between 3° and 5° C. The highest rates were obtained between 115 and 220 mol m^–2 s^–1 with 0.38 div d^–1 for C. criophilum, 0.56 div d^–1 for Synedra sp. and between 0.71 and 0.88 div d^–1 for the other 5 species. A reduction in light intensity from 220 to 46 mol m^–2 s^–1 slowed growth by nearly 50%. These results suggest that the combined effect of temperature and light is one of the factors involved in the limitation of antarctic phytoplankton growth. The low temperatures of the environment do not permit rapid growth, which, even under optimal light conditions remains low. In addition, in the euphotic layer, the overall light energy available for algae is considerably reduced due to turbulence, a factor which exacerbates the reduced growth rate.