The effect of temperature on the post-embryonic growth of Neomysis intermedia Czernlawsky (Crustacea, Mysidacea) under laboratory conditions

The effect of temperature on post-embryonic growth of Neomysisintermedia was investigated under unlimited food conditionsin the laboratory. The effect of temperature on the size ofnewly released animals was negligibly small, but body size wasinversely related to temperature in adults. This was mainlycaused by the difference in the number of molts before maturation.The specific growth rate of N. intermedia increased exponentiallywith a temperature coefficient, Q₁₀ of 4.6 from 0.018 d^–13C to 0.21 d^–1 at 20C in juveniles, and with a temperaturecoefficient of 2.7 from 0.006 d^–1 at 3C to 0.05 d^–1at 25C in adults. The rate in juveniles levelled off above20C, and dropped at 29C. Brood size and brood interval decreasedwith temperature increase, while the daily specific reproductionrate increased. The specific growth rate of gravid females,including production of egg matter, increased exponentiallywith a temperature coefficient of 3.3 from 0.015 d^–1 at10C to 0.093 d^–1 at 25C. The present laboratory experiments confirmed the temperaturecontrol on the growth of N. intermedia suggested in a hyper-eutrophiclake.     

Temperature and Antarctic plankton community respiration

Antarctic plankton community respiration rates were determinedfrom in vitro changes in dissolved oxygen. Oxygen consumptionrates, measured at in situ temperatures between 0 and 6°C,were found to lie in the range 0.3–3.7 µmol O₂ l^–1per 24 h. Water samples were collected between East FalklandIsland and South Georgia, South Atlantic Ocean, and incubatedshipboard in the dark at up to 36 temperatures between –2and 14–C. A respiration rate at each temperature was thendetermined and used to calculate the temperature coefficient(Q₁₀) of Antarctic planktonic community respiration from theArrhenius equation. Fourteen Q₀ values lay in the range 1–3,with four further values >5. This range of temperature coefficientvalues for community respiration is comparable to the publishedrange of values for plankton photosynthesis. Frequency distributionsof temperature coefficients for the two processes show similarmodal Q₁₀5 of 2–3. Thus, this study does not lend supportto the hypothesis of a differential response of photosynthesisand community respiration to low temperature.     

Predation and respiration by the small cyclopoid copepod Oithona similisr: How important is feeding on ciliates and heterotrophic flagellates?

Feeding on natural plankton populations and respiration of thesmall cyclopoid copepod Oithona similis were measured duringthe warm season in Buzzards Bay, Massachusetts, USA. AlthoughO.similis did not significantly ingest small autotrophic andheterotrophic flagellates (2–8 µn), this copepodactively fed on >10 µm particles, including autotrophic/heterotrophic(dino)flagel-lates and ciliates, with clearance rates of 0.03–0.38ml animal^–1 h^–1. The clearance rates increased withthe prey size. O.similis also fed on copepod nauplii (mainlycomposed of the N1 stage of Acartia tonsa with a clearance rateof 0.16 ml animal^–1 h^–1. Daily carbon ration fromthe combination of these food items averaged 148 ng C animal^–1day^–1 (41% of body C day^–1), with ciliates and heterotrophicdino-flagellates being the main food source ({small tilde}69%of total carbon ration). Respiration rates were 020–0.23µl O₂ animal^–1 day^–1. Assuming a respiratoryquotient of 0.8 and digestion efficiency of 0.7, the carbonrequirement for respiration was calculated to be 125–143ng C animal^–1 day^–1, close to the daily carbon rationestimated above. We conclude that predation on ciliates andheterotrophic dinoflagellates was important for O.similis tosustain its population in our study area during the warm season.     

Plankton community respiration in Bransfield Strait (Antarctic Ocean) during austral spring

Community respiration (R) was determined in Bransfield Straitfrom oxygen changes in water samples incubated in borosilicatebottles maintained at in situ temperature. The respiratory electrontransport system (ETS) activity of seawater communities wasalso measured from the same samples. Both data sets were relatedby the regression equation: log R (mg O₂ m^–3 day^–1)=0.462+0.730xlogETS activity mg O₂ m^–3 day^–1) (r=0.80, n=23). Fromthis equation and 37 ETS activity depth profiles, we calculatedthe integrated (0–100 m) community respiration as beingin the range 1.2–4.5 g O₂ m^–2 day^–1 (mean=2.2).These values do not differ significantly from other publishedresults for the Arctic and Antarctic Oceans. Assuming a respiratoryquotient of unity, the areal respiration ranges between 0.45and 1.69 g C m^–2 day^–1 (mean=0.8). This would representan important sink for the primary production reported for BransStrait. The spatial distribution of community respiration showedhigher values associated with the warmer and phytoplankton-richwaters outflowing from Gerlache Strait into Bransfield Strait,and with the front that separates Bellingshausen Sea watersfrom Weddell Sea waters. We suggest that this pattern of distributionmay be related to the transport of organic matter by the BransfieldCurrent along the front.     

Components of Growth and Dark Respiration of Kikuyu (Pennisetum clandestinum Chiov.) at Various Temperatures

Growth and dark respiration were measured in dense, miniatureswards of kikuyu grass grown at constant temperatures of 15,20, 25 and 30 °C. Total respiration over the first 12 hof darkness was very high and CO² efflux per unit surface areavaried from 2.4 to 3.9 g CO₂ m^–2 h^–1 at 15 and 30°C respectively. Such rates were consistent with the correspondinglyhigh net growth rates of 24 and 63 g d. wt m^–2 d^–1and the heavy yields of herbage. When plants were kept in thedark, CO₂ efflux subsequently declined rapidly to a lower, constantrate which was taken to be the maintenance respiration rate.The half-life of the declining phase of respiration averaged10.9 and 6.0 h at 15 and 30 °C respectively, and was curvilinearlyrelated to the specific maintenance respiration rate (m). Therapid decline in respiration was consistent with the low concentrationsof total soluble carbohydrate and starch in the herbage. Valuesof m for lamina and top growth increased with temperature witha Q₁₀ of 2.6 and 1.42 respectively, but m of stems alone wasnot affected by temperature. Using results from this study forkikuyu and from McCree (1974) for sorghum and white clover,it was noted that all three species have similar m when grownat temperatures which are near their respective optimums forgrowth. Kikuyu, Pennisetum clandestinum, growth, respiration, temperature     

Growth and development of Neocalanus flemingeri/plumchrus in the northern Gulf of Alaska: validation of the artificial-cohort method in cold waters

In situ growth and development of Neocalanus flemingeri/plumchrusstage C1–C4 copepodites were estimated by both the artificial-cohortand the single-stage incubation methods in March, April andMay of 2001–2005 at 5–6°C. Results from thesetwo methods were comparable and consistent. In the field, C1–C4stage durations ranged from 7 to >100 days, dependent ontemperature and chlorophyll a (Chl a) concentration. Averagestage durations were 12.4–14.1 days, yielding an averageof 56 days to reach C5, but under optimal conditions stage durationswere closer to 10 days, shortening the time to reach C5 (fromC1) to 46 days. Generally, growth rates decreased with increasingstage, ranging from 0.28 day^–1 to close to zero but weretypically between 0.20 and 0.05 day^–1, averaging 0.110± 0.006 day^–1 (mean ± SE) for single-stageand 0.107 ± 0.005 day^–1 (mean ± SE) forartificial-cohort methods. Growth was well described by equationsof Michaelis–Menten form, with maximum growth rates (G_max)of 0.17–0.18 day^–1 and half saturation Chl a concentrations(K_chl) of 0.45–0.46 mg m^–3 for combined C1–3,while G_max dropped to 0.08–0.09 day^–1 but K_chl remainedat 0.38–0.93 mg m^–3 for C4. In this study, in situgrowth of N. flemingeri/plumchrus was frequently food limitedto some degree, particularly during March. A comparison withglobal models of copepod growth rates suggests that these modelsstill require considerable refinement. We suggest that the artificial-cohortmethod is the most practical approach to generating the multispeciesdata required to address these deficiencies.     

Comparisons of the Respiratory Effluxes of Nodules and Roots in Six Temperate Legumes

The specific respiration rates of nodulated root systems, ofnodules and of roots were determined during active nitrogenfixation in soya bean, navy bean, pea, lucerne, red clover andwhite clover, by measurements on whole plants before and afterthe removal of nodule populations. Similar measurements weremade on comparable populations of the six legumes, lacking nodulesbut receiving abundant nitrate-nitrogen, to determine the specificrespiration of their roots. All plants were grown in a controlled-environmentclimate which fostered rapid growth. The specific respiration rates of nodulated root systems ofthe three grain and three forage legumes during a 7–14-dayperiod of vegetative growth varied between 10 and 17 mg CO₂g^–1 (dry weight) h^–1. This mean value consistedof two components: a specific root respiration rate of 6–9mg CO₂ g^–1 h^–1 and a specific nodule respirationrate of 22–46 mg CO₂ g^–1 h^–1. Nodule respirationaccounted for 42–70 per cent of nodulated root respiration;nodule weight accounted for 12–40 per cent of nodulatedroot weight. The specific respiration rates of roots lackingnodules and utilizing nitrate nitrogen were generally 20–30per cent greater than the equivalent rates of roots from nodulatedplants. The measured respiratory effluxes are discussed in thecontext of nitrogen nitrogen fixation, nitrate assimilation. Glycine max, Phaseolus vulgaris, Pisum sativum, Medicago sativa, Trifolium pratense, Trifolium repens, soya bean, navy bean, pea, lucerne, red clover, white clover, nodule respiration, root respiration, fixation, nitrate assimilation     

Microplanktonic respiration off northern Chile during El Nino 1997-1998

Microplanktonic respiration rates were estimated in waters offthe coast of northern Chile (Antofagasta, 23°S) during ElNiño and pre-El Niño conditions. Three cruiseswere conducted during pre-El Niño summer (January/February1997), El Niño winter (July 1997) and El Niñosummer (January 1998). Oxygen consumption was estimated by theWinkler method using a semi-automatic photometric end-pointdetector. The ranges of microplanktonic respiration rates foundwere 0.11–21.15, 0.03–6.25 and 0.06–9.01 µmolO₂ l^–1 day^–1 during pre-El Niño summer, ElNiño winter and El Niño summer, respectively.Significant differences were found between winter and summerrespiration rates (non-integrated and integrated). The meanintegrated respiration (mixed layer) for pre-El Niñosummer, El Niño winter and El Niño summer was95 ± 51 (SD) mmol O₂ m^–2 day^–1, 50 ±23 (SD) mmol O₂ m^–2 day^–1 and 63 ± 32 (SD)mmol O₂ m^–2 day^–1, respectively. The strong seasonalsignal detected in microplanktonic integrated respiration inthe area seems to be characteristic of the pre-El Niño/ElNiño 1997–98 period. The integrated respirationrates found off Antofagasta are similar to reported values forthe upwelling area off Peru despite methodological differences.A positive significant correlation was found between respirationand water temperature (r = 0.76, P     

Seasonal nitrogen assimilation and carbon fixation in a fjordic sea loch

Carbon (C) fixation and nitrogen (N) assimilation rates havebeen estimated from ¹⁴C and ¹⁵N techniques for a 12 month periodin a Scottish sea loch. The maximum rate of nitrogen assimilated(29.92 mmol N m^–2 day^–1) was in April at the mostseaward station; similar high rates were experienced duringMay at the other stations. Carbon fixation rates were maximal(488–4047 mg C m^–2day^–1) at the time of highphytoplankton biomass (maximum 8.3 mg m^–3 chlorophylla) during May, whilst nitrate concentrations remained >0.7µ.mol l^–1. C:N assimilation ratios suggest nitrogenlimitation only during the peak of the spring bloom, althoughat times nitrogen (nitrate and ammonium) concentration fellto 0.2 µmol l^–1 in the following months. The verticalstability of the water column, influenced by tidal and riverineflushing, varied along the axis of the loch, resulting in markeddifferences between sampling stations. Although ammonium waspreferentially assimilated by phytoplankton, >50% of productionwas supported by nitrate uptake and only during the summer monthswas the assimilation of ammonium quantitatively important.     

Temperature-dependent consumption and gut-residence time in the opossum shrimp Mysis relicta

Maximum daily consumption was estimated for Mysis relicta fedad libitum rations of Daphnia pulex at 4,10,15 and 18°C.Gut-residence time was also evaluated for M.relicta fed clado-ceranprey at 4, 10 and 157deg;C. Mean daily consumption (g dry weightof Daphnia g^–1 dry weight of Mysis day^–1) rangedfrom 6% at 4%C to 12% at 10°. At 18°C, Mysis feedingrate declined to 9% day1. Mean, weight-adjusted consumptionrates exhibited a ‘dome-shaped’ response in relationto water temperature. Consumption rate was highest at 10°Cand lowest at 4°C. Estimated Q₁₀ was more sensitive from4 to 10°C (Q₁₀= 3) than from 10 to 15°C (Q₁₀=1.2). Gut-residencetime for Mysis was inversely related to water temperature, implyingthat evacuation rate increases linearly with water temperature.Feeding and gut-evacuation rates become disassociated at watertemperatures >10°C. As water temperature increased above1°C, relative evacuation rate increased, whereas feedingrate declined. It is postulated that at higher water temperatures,disassociated feeding and gut-evacuation rates reduce the scopefor growth of vertically migrating Mysis and impose a physiologicalconstraint that isolates Mysis from warm, epilimnetic waterduring thermal stratification. ¹Present address: Center for Aquatic Ecology, Illinois NaturalHistory Survey, Sam Parr Biological Station, 6401 Meacham Road,Kinmundy, IL 62854, USA     

WATER EXCHANGE, TEMPERATURE TOLERANCE, OXYGEN CONSUMPTION AND ACTIVITY OF THE NAMIB DESERT SNAIL, TRIGONEPHRUS SP.

Water exchange, temperature tolerance and oxygen consumptionof the snail, Trigonephrus sp., from the southern Namib desertof Namibia were examined and related to activity. At 25°Cand 15% R.H. mean water loss and food and water uptake were5.95 mg. day^–1 and 630 mg.day^–1, respectively. Bodytemperature tracked sand temperature. Snails tolerated sandtemperatures as high as 45°C. Mean ± S.D. oxygenconsumption rates were 32.0 ± 2.94 µlO₂.g totalbody mass^–1.h^–1 at 15°C, when the snails wereactive, and 11.27 µlO₂.g total body mass^–1.h^–1at 25°C, when the snails were inactive. These values are2-6 times lower than those recorded for the similarly sizedmesic snail, Helix aspersa. Activity experiments indicated thatlow ambient temperatures and high humidities were favoured bythe snails. This, together with the burying behaviour of thesesnails during high temperatures, suggests that they limit stressby restricting activity to physiologically-favourable periods,even though more-extreme conditions may be tolerated. (Received 7 June 1990; accepted 20 November 1990)     

A comparison of seasonal growth and development of the copepods Calanus marshallae and C. pacificus in the northern Gulf of Alaska

The juvenile growth rates and development times of subarcticCalanus marshallae and temperate/sub-tropical C. pacificus wereinvestigated during nine cruises (May through October, 2001–04)in the northern Gulf of Alaska. The artificial cohort methodbased on a length-weight regression was used for growth estimatesand the reciprocal of the molting rate for developmental time.The copepodite stage duration ranged from 3 to 16 days for C.marshallae (C1–C4) and 3–23 days for C. pacificus(C1–C5). Seasonally, copepodid growth rates increasedfrom May to October, ranging between 0.055 and 0.291 day^–1(mean ± SE: 0.176 ± 0.008 day^–1) for C.marshallae, while growth rates increased from August to Octoberbetween 0.018 and 0.296 day^–1 (mean ± SE: 0.142± 0.016 day^–1) for C. pacificus. After standardizationto 5°C (Q₁₀ of 2.7), growth rate averaged 0.118 ±0.007 day^–1 and 0.075 ± 0.009 day^–1 for C.marshallae and C. pacificus, respectively. Calanus marshallaegrowth rate is satisfactorily described by a Michaelis–Mentenmodel using chlorophyll-a concentration (r² = 0.33) after temperaturecorrection, but the prediction improves with a composite nonlinearmodel combining body weight into the Michaelis–Mentenfunction (r² = 0.55). Considering the limited range of dataavailable for C. pacificus, the combination of the data forboth species suggests that C. pacificus has a similar functionalresponse to growth despite the differences in the geographicand temporal distributions with C. marshallae. Measured juvenilegrowth rates of the two Calanus species in this study were comparableto other calanoid species in the same area and showed reasonableagreement to Calanus growth models but less with global copepodgrowth models.     

Ontogeny of growth, respiration and feeding rate of the freshwater calanoid copepod Eudiaptomus graciloides

The calanoid copepod, Eudiaplomus graciloides, was reared fromegg to adult on uni-algal diets (0.1. 0.5 and 2.5 mg dry wt1^–1) using the green alga, Chlamydomonas reinhardtii,as food, or on a mixed diet consisting of Lake Esrom water filteredthrough a plankton net with pore size 45 µm and supplementedwith C. reinhardtii (2.5 mg dry wt 1^–1). On the mixeddiet at 21.0°C growth in body dry wt (W, µg dry wt)was exponential, and the growth constants were 0.21 day^–1in the early to mid juvenile stage (N1 - C4) and 0.11 day^–1in the late juvenile to early adult stage (C4-A). At 14.5°Cthe corresponding growth rate constants were 0.10 and 0.08 day^–1.Similar growth rates were found at uni-algal concentrationsof 0.5 and 2.5 mg dry wt I^–1, and it was argued that thethreshold concentration for growth in Eudiaptomus was closeto 0.1 mg dry wt I^–1. The clearance (C, ml h^–1)of copepodites was measured on the uni-algal diets. The constantsof the regression (C = aW^b) were: a = 0.125, b = 0.858 (2000C. reinhardtii ml^–1), a = 0.068, b = 0.849 (10 000), a= 0.028, b = 0.875 (50 000). Ingestion rates were calculatedfrom the clearances and the average algal concentrations. Atthe three food levels the average daily rations were 30, 67and 125% of body dry wt. The respiration rate (R, nl O₂ h^–1)was measured in individuals reared on the mixed diet. The constantsof the regression (R = aW^b) were: a = 4.82, b = 1.07 (nauplii,14.5°C), a = 4.17, b = 0.904 (copepodites and adults, 14.5°C),a = 6.87, b = 0.757 (copepodites and adults, 21.0°C). Nosignificant difference in the respiration rate of copepoditesreared on uni-algal diets and the mixed diet could be demonstrated.Energy budgets were calculated. The assimilation efficiencyand the gross growth efficiency of copepodites decreased markedlywith increasing food concentration, the net growth efficiencyvaried from an average of 0.44 at the lowest algal concentrationto 0.60 on the mixed diet. The results are discussed in relationto previous findings with both freshwater and marine copepods.     

Ecological studies on the phytoplankton of Boknafjorden, western Norway. II. Environmental control of photosynthesis

Both predicted (incubator) and measured (in situ) ¹⁴C-assimilationrates were studied from February to November 1981 at three stationsin Boknafjorden, a deep silled fjord of western Norway. Sampleswere taken from different light depths within the euphotic zone.A high degree of conformity was found between the two approaches.Daily values of carbon assimilation integrated over the euphoticzone varied between 0.05 and 1.4 g C m^–2. Yearly primaryproduction varied between stations from 82 to 112 g C m^–2(120–148 g C m^–2 when based on average light conditions).The light-saturation curve parameters ^B and P^B_max ranged from0.0056 to 0.0537 mg C mg Chla^–1 h^–1 µE^–1m² and from 0.7 to 8.5 mg C mg Chla^–1 h^–2 (in situassimilation numbers ranged from 0.9 to 9.3 mg C mg Chla^–1h^–1) respectively, which compare well with those publishedfrom the northwestern side of the Atlantic. The overall importanceof light in controlling photosynthesis throughout the year wasrevealed by the light utilization index , estimated to be 0.43mg C mg Chla^–1 E^–1 m². The maximum quantum yieldwas encountered on August 17, with 0.089 mol CE^–1. Chla/Cratios above and below 0.010 were found to be typical for shade-and light-adapted cells respectively. Assimilation numbers andgrowth rates were linearly related only when considering light-adaptedcells. Consistent with the findings of this study, the applicabilityof I_K, ^B and P^B_max as indicators of light-shade adaptation propertiesshould be questioned. Maximum growth rates were encounteredduring an autumn bloom of the dinoflagellate Gyrodinium aureolum(1.0 doublings day^–1), while 0.7–0.8 doublings day^–1were found for a winter bloom (water temperature of 2°C)of the diatom Skeletonema costatum. No unambiguous temperatureeffect on assimilation number and growth of phytoplankton couldbe recognized in Boknafjorden. A tendency towards increasedassimilation numbers coinciding with increased water columnstability was revealed. The highest P^B_max values were oftenencountered at almost undetectable nutrient concentrations.At least during summer this could be attributed to recyclingof nutrients by macro- and/or microzooplankton, responsiblefor a greater part of the primary production now being grazeddown. This study supports the convention that the depth of theeuphotic zone may extend considerably below the 1% light depth.     

Respiratory Efflux in Relation to Temperature of Simulated Swards of Perennial Ryegrass with Contrasting Soluble Carbohydrate Contents

Fully light-intercepting simulated swards of S24 perennial ryegrasswere exposed to contrasting environmental conditions in a growthroom for 4 days. Half experienced 20 h days of 120 Wm^–2(400–700. nm) and 5 °C, and came to have a WSC (watersoluble carbohydrate) content of 235 mg g^–1 and half 4h days of 20 Wm^–2 and 25 °C leading to a WSC of 25mg g^–1. Their rates of CO₂ efflux were monitored at anumber of temperatures during an 8 h dark period; half experiencedincreasing (5–30 °C) and half decreasing (30–5°C) temperatures. The ‘high’ WSC swards hadrespiration rates of 3.7 mg CO₂ g^–1 (d. wt) h^–1at 15 °C, and the ‘low’ swards 0.8 mg CO₂ g^–1h^–1. The order in which the temperatures were experiencedwas immaterial. Even the ‘low’ WSC swards showedno evidence of a respiratory decline during the dark periodthat could be attributed to substrate shortage. The relationshipbetween temperature and CO₂ efflux was best represented by logisticcurves. Even so, a Q₁₀ of 2 fitted the data reasonably well,at least up to 20 °C, and has practical advantages wheninterpolating estimated between measured values of respirationin the construction of a carbon balance sheet. Lohum perenne L., ryegrass, respiration, temperature, Q₁₀, soluble carbohydrate content, simulated sward     

Growth and development of Metridia pacifica (Copepoda: Calanoida) in the northern Gulf of Alaska

Juvenile growth and development rates for Metridia pacifica,one of the dominant larger copepods in the subarctic Pacific,were investigated from March through October of 2001–2004in the northern Gulf of Alaska. The relationship between prosomelength (PL, µm) and dry weight (DW, µg) was determined:log₁₀ DW = 3.29 x log₁₀ PL – 8.75. The stage durationsof copepodites ranged from 3 to 52.5 days but were 8–15days under optimal condition. Seasonally, growth rates increasedfrom March to October and typically ranged between 0.004 and0.285 day^–1, averaging 0.114 ± 0.007 day^–1(mean ± SE). After standardization to 5°C (Q₁₀ of2.7), growth rates averaged 0.083 ± 0.005 day^–1and were significantly correlated to chlorophyll a, with saturatedgrowth rates of 0.149 day^–1 for C1–C3, 0.102 day^–1for C4–C5 and 0.136 day^–1 for all stages combined.Measured juvenile growth rates were comparable with specificegg production rates in this species. The comparisons of ourrates in this study with those predicted by the global modelsof copepod growth rates suggested that further refinement ofthese models is required.     

Feeding and metabolism of the siphonophore Sphaeronectes gracilis

The in situ predation rate of the siphonophore Sphaeronectesgracilis was estimated from gut content analysis of hand-collectedsiphonophores and from laboratory data on digestion rates ofprey organisms. At daytime prey densities of 0.25 copepods 1^–1,S. gracilis was estimated to consume 8.1 – 15.4 prey day^–1siphonophore^–1. From data on abundances of siphonophoresand copepods, S. gracilis was estimated to consume 2–4%of the copepods daily. In laboratory experiments, ingestionrates averaged 13.8 prey day^–1 siphonophore^–1 atprey densities of 5 copepods 1^–1 and 36.9 at 20 copeods1^–1. This was equivalent to a specific ingestion rate(for both carbon and nitrogen) of –17% day^–1 and45% day^–1, respectively, while specific ingestion in situwas only 2% day^–1. Ammonium excretion averaged 0.095 µg-atsiphonophore^–1 day^–1 at 5 prey 1^–1, and 0.162at 20 prey 1^–1. The specific respiration (carbon) andspecific excretion (nitrogen as ammonium) were calculated tobe 3% day^–1 at the lower experimental food level, and5% day^–1 at the higher food level. ¹Contribution from the Catalina Marine Science Center No. 66. ²Present address: Dept. of Biology, University of Victoria,Victoria, B.C., Canada V8W 2Y2.     

The Effect of Root Temperature on Growth and Uptake of Ammonium and Nitrate by Brassica napus L. cv. Bien venu in Flowing Solution Culture: II. UPTAKE FROM SOLUTIONS CONTAINING NH4NO3

Macduff, J. H., Hopper, M. J. and Wild, A. 1987. The effectof root temperature on growth and uptake of ammonium and nitrateby Brassica napus L. CV. Bien venu in flowing solution culture.II. Uptake from solutions containing NH₄NO₃.—J. exp. Bot.38: 53–66 The effects of root temperature on uptake and assimilation ofNH₄⁺ and NO₃^– by oilseed rape (Brassica napus L. CV. Bienvenu) were examined. Plants were grown for 49 d in flowing nutrientsolution at pH 6?0 with root temperature decrementally reducedfrom 20?C to 5?C; and then exposed to different root temperatures(3, 5, 7, 9, 11, 13, 17 or 25?C) held constant for 14 d. Theair temperature was 20/15?C day/night and nitrogen was suppliedautomatically to maintain 10 mmol m^–3 NH₄NO₃ in solution.Total uptake of nitrogen over 14 d increased threefold between3–13?C but was constant above 13?C. Net uptake of NH₄⁺exceeded that of NO₃^– at all temperatures except 17?C,and represented 47–65% of the total uptake of nitrogen.Unit absorption rates of NH₄⁺ and of 1?5–2?7 for NO₃^–suggested that NO₃^– absorption was more sensitive thanNH₄⁺ absorption to temperature. Rates of absorption were relativelystable at 3?C and 5?C compared with those at 17?C and 25?C whichincreased sharply after 10 d. Tissue concentration of N in theshoot, expressed on a fresh weight basis, was independent ofroot temperature throughout, but doubled between 3–25?Cwhen expressed on a dry weight basis. The apparent proportionof net uptake of NO₃^– that was assimilated was inverselyrelated to root temperature. The results are used to examinethe relation between unit absorption rate adn shoot:root ratioin the context of short and long term responses to change ofroot temperature Key words: Brassica napus, oilseed rape, root temperature, nitrogen uptake     

Dynamics of herbivorous grazing by the heterotrophic dinoflagellate oxyrrhis marina

In a series of batch experiments in the dark the heterotrophicdinoflagellate Oxyrrhis marina grazed three phytoplankton prey(Phaeodactylun tricornutum, Isochrysis galbana and Dunaliellateriolecta) with equal efficiency. Growth rates of the dinoflagellateranged between 0.8 and 1.3 day–1 Maximum observed ingestionrates on a cell basis varied according to the size of the preyfrom about 50 cells flagellate^–1 day^–1 when D.tertiolectawas the prey to 250–350 cells fiagellate^–1 day^–1when the other species were eaten. However, when compared ona nitrogen basis, ingestion rates were independent of prey type.Both ingestion and growth ceased when prey cell concentrationsfell below a threshold concentration of about 10⁵ cells ml^–1.Maximum specific clearance rates were 0.8x10⁴0ndash;5.7x10⁴it day which is considerably lower than that found for heterotrophicdinoflagellates in oceanic waters and may explain why O.marinagenerally thrives only in productive waters. The timing of NHregeneration was linked to the C:N ratio of the prey at thestart of grazing. Regeneration efficiencies for NH₄. never exceeded7%; during the exponential phase and were 45% well into thestationary phase. These results are comparable to those obtainedwith heterotrophic flagellates and demonstrate that the bioenergeticpatterns of grazing and nutrient cycling by different protozoaare very similar. Moreover, they support the notion that toachieve 90+% nutrient regeneration in the open ocean, as iscurrently believed, the microbial food loop must consist ofmultiple feeding steps. Alternatively, nutrient regenerationefficiencies may be considerably lower than 90%.     

Respiration losses in planktonic green algae cultivated in raceway ponds

Rates of respiratory oxygen uptake were measured in darkenedsamples of green microalgae (Coelastrum sphaericum, Scenedesmusfalcatus) growing in raceway ponds under field conditions andindoors. The rates measured over 6–26h varied between1 and 1.5 and 8.25 µl O₂ mg^–1 h^–1 and dependedon incubation, temperature, time in the dark, and on the temperatureand irradiance at which the algae were cultivated before. Q₁₀values ranged from 1.43 to 1.68. Arrhenius relationships describedthe influence of temperature upon respiration rates below theoptimum temperature, even after many hours of incubation inthe dark. Respiration rates were lower after growth at optimaltemperature than after cultivation at other temperatures. Thelight history also influenced the rates, being high when thealgae were darkened after exposure to high irradiance and lowerafter weaker pre-illumination. For the algae under study theoverall loss during 12h of darkness was estimated to be 2–10%of the biomass prior to darkening. Higher losses are expectedfor natural conditions and stronger irradiances.