Postmetamorphic Growth and Metabolism of Long-Spined Black Sea Urchin (Diadema antillarum) Reared in the Laboratory

Postmetamorphic growth and metabolism measurements were obtained on two cohorts of laboratory-reared Diadema antillarum. The cohorts grew linearly from less than 1 mm to over 43 mm. Daily growth averaged 0.097 and 0.11 mm d^-1, respectively, for the two cohorts, and was found to differ significantly. Urchin metabolism was examined by a series of simultaneous measurements of oxygen consumption and ammonium excretion over 16 days on starved juveniles ranging 16.5 to 18.3 mm. Metabolic activity under conditions of starvation was used as a test of the viability of urchins reared in the laboratory with cultured food resources. Catabolic activity differed from the first week of starvation compared to the second. Metabolic response included: (1) a 2.2-fold increase in oxygen consumption rate; (2) 50% decline in ammonium excretion rate; and (3) a 5.1-fold increase in oxygen to nitrogen ratio. These measurements are consistent with a shift from almost pure protein catabolism during the first seven days of starvation to a lipid : protein catabolic ratio of 1 : 1 after the first week. Growth and metabolism experiments of this type are seen as a first step towards optimizing laboratory culture techniques of this species.     

Ammonium and phosphate excretion in three common echinoderms from Philippine coral reefs

The ammonium and phosphate excretion and oxygen consumption of three species of echinoderms (Tripneustes gratilla, Protoreaster nodosus and Ophiorachna incrassata) commonly encountered in Philippine coral reefs were investigated in relation to time of day (i.e. daytime between 10:00 and 12:00 h vs. nighttime between 22:00 and 24:00 h) and their recent feeding history (i.e. recently-collected vs. short-term starvation for 3+/-1 days). The experiment used whole organism incubations and followed a nested hierarchical design. Ammonium excretion rates were 1447+/-310 nmolg(-1) DWh(-1) (mean+/-S.E., n=24) for T. gratilla, 361+/-33 for O. incrassata and 492+/-38 for P. nodosus. Ammonium excretion differed significantly among species, time of incubation and recent feeding history. Interaction between species and recent feeding history was also significant. The organisms excreted more ammonium during daytime except for starved specimens of O. incrassata. In addition, animals that were starved in the laboratory for a few days had a tendency to excrete more ammonium than recently-collected specimens. Phosphate excretion rates were 25+/-13 nmolg(-1) DWh(-1) for T. gratilla, 10+/-2 for O. incrassata and 4+/-1 for P. nodosus. There were no significant differences in phosphate excretion among the three species of echinoderms, their recent feeding history and time of day. Oxygen consumption rates were 286+/-24 μg O(2)g(-1) DWh(-1) for T. gratilla, 64+/-3 for O. incrassata and 54+/-3 for P. nodosus. Oxygen consumption differed significantly among species and recent feeding history but differed only slightly with time of incubation. There was a significant correlation between oxygen consumption and ammonium excretion (r=0.48, P=0.018), and between oxygen consumption and phosphate excretion (r=0.41, P=0.047) for T. gratilla. The nutrient excretion by tropical echinoderms is another pathway by which inorganic nutrients are regenerated in coral reef communities. However, the quantity of nutrients excreted is dependent on the species of echinoderms, their nutritional status and time of day.     

中华绒螯蟹亲蟹的饥饿代谢研究

1998年 10～ 12月 ,对体重为 5 4 .5 9(± 2 .37) g的亲蟹在 2 0 (± 0 .5 )℃温度条件下进行饥饿实验 ,研究了饥饿对中华绒螯蟹亲蟹代谢的影响 .结果表明 ,经过 30d的饥饿处理 ,亲蟹的耗氧率降低为摄食状态的 5 0 .0 % ;CO2 排出率减小为摄食状态的 6 3.4 % ;NH3 N排泄率减小为 5 9.1% .耗氧率和CO2 排出率、NH3 N排泄率的变化差别较大 ,耗氧率的减小可分为 4个阶段 ,而CO2 排出率和NH3 N排泄率的减小仅可分 3个阶段 .与此同时 ,亲蟹的标准代谢水平同样受到饥饿的影响 ,饥饿 30d后 ,由 4 .4 5J·g-1·h-1减小为 2 .36J·g-1·h-1;在饥饿亲蟹的代谢中 ,脂肪消耗最多 ,其次是碳水化合物 .     

Metabolic depression and whole-body response to enforced starvation by Crassostrea gigas postlarvae

Physiological and biochemical measurements were performed on six oyster (Crassostrea gigas) cohorts, in order to: (a) investigate the whole-body response (growth, energy content, metabolic and excretion rates) of 2-week-old postlarvae (spat) to enforced (0-8 days) starvation, and (b) test the potential use of three aerobic enzyme systems as indices of physiological condition. Starvation resulted in exponential reduction of postlarval metabolic and excretion rates, as well as a linear decrease in enzyme activity. These response mechanisms effectively limited the loss of endogenous reserves after 2 days of starvation and maintained the oyster's functional integrity over prolonged (8 days) starvation. Proteins appeared to be selectively conserved during short-term (2 days) starvation, as suggested by a decrease in total protein content, while maintaining constant weight-specific enzyme activity. Postlarvae starved for 2 days exhibited relatively higher lipid losses, lower mortality and lower metabolism than metamorphosing stages, thus suggesting a greater buffering capacity to starvation in the former. The activity of the electron transport system may be a useful indicator of long-term stress or developmental condition of oyster postlarvae, while citrate synthase and cytochrome oxidase could be used as indicators of growth rate. None of these enzyme systems is recommended as an index of aerobic metabolism during short-term starvation.     

Respiration and ammonia excretion of the shrimpCrangon crangon L.: Metabolic response to prolonged starvation

Summary Oxygen consumption and ammonia excretion were measured simultaneously in 25 individual shrimps (C. crangon) every two days during a 30-day imposed starvation.The first response to starvation was a 10% decrease in O₂ consumption and a 25% decrease in ammonia excretion. Following this, O₂ consumption decreased sharply while ammonia excretion tended to rise. From the 14th day until the end of the experiment, the rates of each remained steady, the respiratory rate being about 60% below and rate of excretion about 30% above control values.From the O:N ratio it appeared that carbohydrate reserves were quickly exhausted (3–4 days) and that lipids and proteins were the main substrates oxidized to meet the energetic requirements ofC. crangon. After 2 weeks of starvation the O:N ratio remained constant near a value of 8, indicating that only proteins were being utilised; a 50% loss of body protein after 30 days suggested that structural proteins were heavily catabolized. The meatabolic response ofCrangon to starvation (although seasonal variations must be considered) appears to depend mainly on high nitrogen requirements.     

Excretion and respiration rates of Neomysis integer (Mysidaceae): effects of temperature,sex and starvation

The combined effects of temperature, sex and length of pre-experimental starvation period on respiration, ammonia and inorganic phosphate excretion of the mysid shrimp Neomysis integer were studied in laboratory experiments. Of these variables, temperature had the strongest effect. A rise in experimental temperature from 6 to 16 °C increased the metabolic rates by a factor of 2 to 3.Weight-specific respiration rates of females were slightly lower than those of males. However, these differences could be attributed to differences in size. Sex did not significantly affect ammonia and inorganic phosphate excretion.A prolongation of the pre-experimental starvation period from 6 to 30 h reduced ammonia excretion of Neomys integer, but had no impact on oxygen consumption rates. Accordingly, the atomic O : N ratio increased in starved specimens. There were no discernables effects of the variables studied on atomic O : P and N : P ratios.     

Effects of starvation on oxygen consumption, ammonia excretion and biochemical composition of the hepatopancreas on adult males of the False Southern King crab Paralomis granulosa (Crustacea, Decapoda)

Adults of the False Southern King crab, Paralomis granulosa, were starved between 0 and 12 days to evaluate the impact of fasting on the oxygen consumption, nitrogen excretion, O/N ratio and changes on biochemical composition of the hepatopancreas. During the experiment, no mortalities were recorded; physiological changes were detected after 6 days of fasting with an increase of nitrogen excretion (p<0.05). After 9 days of starvation, the crabs showed a maximum decrease in the lipid content (4.3+/-1.2%, p<0.05), accompanied by an increase in oxygen consumption (53.1+/-10.9 microg O2 h(-1) g(-1)). The lowest O/N ratio was detected after 6 days (6.4+/-4.8) and the highest after 12 days of fasting (38.1+/-20.4), indicating that initially crabs utilized proteins as source of energy , followed by lipids. Moreover, after 12 days, there was a significant increase in the hepatosomatic index (HI) and total lipid content (9.7+/-1.0%, p<0.05), which could be associated with the re-absorption of other tissues to the hepatopancreas. Our results provide new information on this species that shows a different pattern of adaptation for each period of starvation and a good correlation between physiological and biochemical parameters. The ability to withstand and recover from periods of nutritional stress is an important adaptation for survival of any organism that must sporadically endure periods of limited food supply.     

Effect of natural and laboratory diet on O : N ratio in juvenile lobsters (Homarus americanus)

Oxygen consumption and ammonia excretion rates of juvenile lobsters spanning the size range from shelter-restricted to vagile (7-60 mm CL, carapace length) were measured. There are no significant size-dependent break points in the slope of oxygen consumption or nitrogen excretion rates versus weight in freshly caught wild or laboratory fed lobsters. This suggests that there are no inherent changes in energy metabolism in juvenile lobster in the 7-60 mm CL range (stage V to adolescent lobsters), despite major behavioral shifts related to foraging and shelter use. In addition, the O : N ratio of freshly caught wild lobsters (15.7+/-7.4, mean+/-S.D.) is not significantly different from that of lobsters fed brown algae (13.4+/-4.9) or a mixed carbohydrate/protein diet (13.7+/-6.8) in lab. The O : N ratio of wild lobsters is significantly higher than lobsters fed a high protein diet (7.5+/-2.5) in the lab. This suggests that carbohydrates, particularly algal-derived carbohydrates, make up a significant portion of the metabolic fuel of wild juvenile lobsters from settlement through adolescence.     

Monolayer expansion induces an oxidative metabolism and ROS in chondrocytes

This study tests the hypothesis that articular chondrocytes shift from a characteristically glycolytic to an oxidative energy metabolism during population expansion in monolayer. Bovine articular chondrocytes were cultured in monolayer under standard incubator conditions for up to 14 days. Cellular proliferation, oxygen consumption, lactate production, protein content, ROS generation and mitochondrial morphology were examined. Lactate release increased ∼5-fold within 1 week, but this was limited to ∼2-fold increase when normalized to cellular protein content. By contrast, per cell oxidative phosphorylation increased 98-fold in 1 week. The increase in oxidative phosphorylation was evident within 24 h, preceding cell proliferation and was associated with augmented reactive oxygen species generation. The autologous chondrocyte implantation procedure requires 14-21 days for population expansion. The alterations in metabolic phenotype we report within 7 days in vitro are thus pertinent to autologous chondrocyte implantation with significant implications for the chondrocyte functionality.     

Phosphate limitation stress induces xylitol overproduction by Debaryomyces hansenii

The physiological responses of xylose-grown Debaryomyces hansenii were studied under different nutritive stress conditions using continuous cultivation at a constant dilution rate of 0.055 h⁻¹. Metabolic steady-state data were obtained for xylose, ammonium, potassium, phosphate and oxygen limitation. For xylose and potassium limitation, fully oxidative metabolism occurred leading to the production of biomass and CO₂ as the only metabolic products. However, potassium-limiting cultivation was the most severe nutritional stress of all tested, exhibiting the highest xylose and O₂ specific consumption rates along with the lowest biomass yield, 0.22 g g⁻¹ xylose. It is suggested that carbon was mainly channelled to meet the cellular energy requirements for potassium uptake. For the other limiting nutritional conditions increasing amounts of extracellular xylitol were found for ammonium, phosphate and oxygen limitation. Although xylitol excretion is not significant for ammonium limitation, the same is not true for phosphate limitation where the xylitol productivity reached 0.10 g l⁻¹ h⁻¹, about half of that found under oxygen-limiting conditions, 0.21 g l⁻¹ h⁻¹. This work is the first evidence that xylitol production by D. hansenii might not only be a consequence of a redox imbalance usually attained under semi-aerobic conditions, but additional physiological mechanisms must be involved, especially under phosphate limitation. Cell yields changed drastically as a function of the limiting nutrient, being 0.22, 0.29, and 0.39 g g⁻¹ xylose for potassium, oxygen and phosphate limitation, respectively, and are a good indicator of the severity of nutritive stress.     

温度和盐度突变对菲律宾蛤仔斑马蛤耗氧率和排氨率的影响

为研究温度和盐度对蛤仔新品种斑马蛤耗氧排氨的影响,以野生蛤仔为对照,实验设置15、20、25、30和35℃五个温度梯度和20、25、30、35和40五个盐度梯度,结果表明:温度和盐度对斑马蛤的耗氧率和排氨率影响显著（P < 0.05）。在温度15-35℃内,随着温度的增加,耗氧率和排氨率整体上呈增加的趋势。在20-40盐度内,耗氧率随着盐度的升高先减少后增加,排氨率随着盐度的升高先增加后减少,在盐度为30时达到最高值。在水温为15℃,盐度20-40内,斑马蛤的O:N为9.534-62.008;在盐度为35,水温在15-35℃内,斑马蛤的O:N是20.700-74.138。与野生蛤仔比较,斑马蛤的耐高温能力要强于野生蛤仔,从Q₁₀的变化反映出斑马蛤对温度的敏感性相对较弱,适应温度变化的能力比较强;斑马蛤的耐低盐和耐高盐能力强于野生蛤仔。研究结果为进一步完善蛤仔斑马蛤的人工养殖技术提供参考。     

Energy metabolism and nutrient oxidation in young pigs and rats during feeding, starvation and re-feeding

The investigation included individual measurements of energy metabolism and oxidation of nutrients in 12 castrated male pigs (Sus scrofa) (20-40 kg) and 12 male rats (Rattus norvegicus) (65-105 g). Measurements were carried out in 5-6 days balance periods with ad libitum feeding, followed by 3-4 days of starvation and 4 days of re-feeding. O2 consumption and CO2 production were measured by open-air-circuit respiration units. In the feeding period, protein retention in relation to metabolic live mass (kg(0.75)) was identical for pigs and rats, while there was a tendency of a higher fat retention in pigs than in rats. A substantial part of digested carbohydrate was not oxidized, but transferred to fat metabolism without significant differences (P > 0.05) between pigs and rats (18% vs. 22%). During starvation, nitrogen excretion in urine decreased to 226 mg/kg(0.75) in pigs and to 429 mg/kg(0.75) in rats, indicating a lower rate of body protein degradation in pigs. Heat production was reduced to 592 and 338 kJ/kg(0.75), while the contribution of heat from oxidation of protein (OXP), carbohydrate (OXCHO) and fat (OXF) showed the same pattern for pigs and rats during all periods. Heat production during feeding and re-feeding was covered by OXP+OXCHO with no OXF and reversibly after 2 days of starvation by OXP+OXF with no OXCHO. The rat may be a suitable model for pigs regarding general patterns of quantitative nutrient partition, but any direct application of results measured with rats to pigs shall be taken cautiously, keeping in mind that modern pigs have been selected for a high growth rate and protein deposition which has not been the case for the laboratory rat.     

Effect of food shortage and temperature on oxygen consumption in the lesser mealworm, Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae)

Abstract.  Temperature and food availability are limiting factors for the establishment of tropical insects in temperate countries. In the alien pest beetle, Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae), starvation and temperature have a significant impact on metabolic rate with oxygen consumption ranging from 0.5 µmol/g fresh mass (FM)/h at 12 °C to 3.4 µmol/g FM/h at 24 °C. At 12 °C, oxygen consumption decreased continuously during an entire period of starvation. However, at 16, 20 and 24 °C, beetles display a marked hyperactivity that leads to an increase in the oxygen consumption level during the first week of starvation, followed by a steep decrease until the end of the starvation period. Oxygen consumption either does not decline in fed beetles (observed at higher temperatures) or declines at a much shallower rate than in starved beetles (observed at cooler temperatures). During the first week of refeeding, Oxygen consumption rose steeply at 16, 20 and 24 °C before levelling off to the initial value ( t ₀). At 12 °C, no compensation process was observed during recovery. This study reveals that an important threshold in the biology of A. diaperinus lies between 12 and 16 °C, leading to the onset of reduced locomotor activity and the promotion of survival to the detriment of reproduction. This 'sit and wait' behaviour is proposed as an adaptive strategy (i.e. inactivity and lower oxygen consumption coupled with low energetic requirements and high recovery abilities). Such behaviour and the observed hyperactivity were rarely described in insects before the present study. Together, the previous and present results suggest that A. diaperinus populations are likely maintained in temperate regions by immigration from warmer situations.     

温度和摄食对溪红点鲑幼鱼呼吸代谢的影响

在不同水温［(5.5±0.5) ℃、(8.5±0.5) ℃、(11.5±0.5) ℃、(14.5±0.5) ℃、(17.5±0.) ℃］条件下,分别测定了饱食和空腹状态下溪红点鲑幼鱼的耗氧率和排 氨率,分析了温度和摄食对溪红点鲑幼鱼呼吸代谢的影响.结果表明：饱食后,5个温度梯度组溪红点鲑幼鱼的耗氧率和排氨率均迅速上升,达最大值后缓慢下降,并逐渐恢复到初始水平;饱食状态下,溪红点鲑幼鱼耗氧率（OR）和排氨率（NR）与温度（t）的回归方程分别为OR=-0.0601t⁴+2.5542t³-39.256t²+276.26t-598.75(n=650,R²=1,4.5 ℃4+0.0826t³-1.2318t²+8.6186t-18.838(n=650,R²=1,4.5 ℃0.9738(n=650,R²=0.9974,4.5 ℃1.0896( n=650,R²=0.9977,4.5 ℃相似文献   

Energetic demands of larval krill, Euphausia superba, in winter

Metabolic rates of larval and juvenile krill, Euphausia superba, were measured on board ship during three winter cruises west of the Antarctic Peninsula (June-July 1987, June 1993, and June 1994), and also under different temperature regimes and feeding conditions during long-term maintenance in the laboratory (Palmer Station, winter 1993). A mean oxygen consumption and nitrogen excretion ratio of 31.1 measured on board ship at ambient ocean temperatures suggested that larval and juvenile krill from ice-covered waters were primarily herbivorous. Results from both shipboard and laboratory experiments demonstrated that oxygen consumption increased with temperature, but that larvae subjected to acute temperature increases exhibited higher rates. Experiments conducted at near ambient water temperatures for winter were also conducted to test the effect of habitat on the energy requirements of larval and juvenile krill. A comparison of the field and laboratory studies conducted at −1.5 to −1.8 °C showed that larvae from ice-covered waters and fed larvae in the laboratory had oxygen consumption rates significantly higher than those of larvae collected from open, i.e. ice-free, water and those starved in the laboratory. Results of the comparison lend support to the concept that in winter, larval and juvenile krill are better fed in ice-covered waters than in open water, and to the hypothesis that ice biota in the pack ice are an important food resource in winter for larval and juvenile krill.     

Metabolic utilization of body stores during the early life of whitefish, Coregonus lavaretus L.

Patterns of oxygen consumption, ammonia and urea excretion were monitored during late embryogenesis, i.e. 5 days before mass hatching and 12 days during the free-swimming stage of whitefish larvae, Coregonus lavaretus. Oxygen consumption increased from 1.31 to 2.53 mgO₂ h⁻¹× 10³ eggs⁻¹ at hatching. Fasted, free-swimming larvae showed increasing oxygen consumption to the tenth day after hatching when it reached 5.52 mgO₂h⁻¹× 10³ larvae⁻¹. Ammonia and urea excretion increased during pre-hatching period from 52.1 to 163.2 and 26.8 to 51.4 μgh⁻¹× 10³ eggs⁻¹, respectively. The nitrogen excretion rate increased between the sixth and tenth day of fasting, i.e. for ammonia from 117.7 to 160.9 and for urea from 35.8 to 52.5 μg h⁻¹× 10³ larvae⁻¹. Cumulative data on nitrogen and energy metabolism indicated that during late embryogenesis, and up to the fifth day after hatching, protein dominated in the energy expenditure. During the free swimming stage, the ratio of fat to protein in energy expenditure rose from 0.86 to 1.99. Combined data for several fish species indicated high dependance of oxygen uptake during the hatching period on egg size and temperature.     

Changes with time after capture in the metabolic activity of the carnivorous copepod Euchaeta norvegica Boeck

The rates of respiration and ammonium excretion of the carnivorous copepod Euchaeta norvegica Boeck decreased by 40 and 70%, respectively, during the first ≈10 h after capture. ETS (electron transport system) activity decreased in parallel with the rate of respiration. Increasing O/N and decreasing N/P atomic ratios during incubation indicated a change from protein to lipid metabolism, suggesting that starvation was the major factor responsible for the depression of the metabolic rates after capture. The adenylate energy charge (EC) ratio was significantly lower during the initial 13 h after capture than subsequently, caused mainly by an elevated AMP level. The total content of adenine nucleotides increased during this period of lowered EC. Starvation could also have been responsible for these changes in the adenine nucleotide levels through degradation of RNA. Our earlier interpretation that the lowered EC values after capture reflected capture stress has not been confirmed. The lactate level of E. norvegica just after capture was low (≈0.1 μg·mg dry wt^?1) and thus not indicative of any oxygen debt.     

The effects of different cycles of starvation and re‐feeding on growth and body composition in rainbow trout (Oncorhynchus mykiss,Walbaum, 1792)

This study was designed to investigate the effects of starvation and re‐feeding cycles on the growth performance and body chemical composition of Oncorhynchus mykiss juveniles. A total of 360 juveniles with initial mean weights (IW) of 8.46 ± 0.07 g (n = 360) were stocked into 400‐L tanks in triplicate for each group, with 30 juveniles per tanks. The control group received regular feed, as is the common practice. The three other groups were periodically starved: 1 day starvation followed by 6 days re‐feeding (S1), 2 days starvation followed by 5 days re‐feeding (S2) and 3 days starvation followed by 4 days re‐feeding (S3). The experiment lasted for 10 weeks, over the course of which the water flow rate was 4 L min^?1 and the water quality parameters determined as: temperature 14.4 ± 1.1°C, oxygen 8.2 ± 0.4 mg L^?1 and pH 7.5 ± 0.2. At the end of the study, S1 had the best growth performance (final weight, specific growth rate, average daily growth) of all test groups (P < 0.05). The lowest daily feed intake (DFI) and growth performance parameters were observed in S3 (P < 0.05), while protein efficiency ratio (PER), net protein utilization (NPU) and lipid efficiency ratio (LER) were higher in the S3 fish group than in the other groups (P < 0.05). Whole body protein and lipid contents were highest in S1 fish. The hepatosomatic index (HSI) and viscerosomatic index (VSI) were significantly different among groups (P < 0.05). Feed conversion ratio (FCR) was significantly lower in starvation groups S1, S2 and S3 than in the control (P < 0.05). Compensation coefficient (CC) values were higher than 1 in all starvation groups. The concluding indicate that rainbow trout exposed to 1 and 2 days of starvation in week cycles could achieve over compensation compared to the control. Additionally, partial growth compensation and improved feed utilization could be achieved in a starvation group within 3 days in a week, by beginning with the juvenile size over a 10‐week experimental period.     

Seasonal variations in the rates of aquatic and aerial respiration and ammonium excretion of the ribbed mussel, Geukensia demissa (Dillwyn)

Aquatic and aerial rates of oxygen consumption and ammonium excretion of ribbed mussels, Geukensia demissa (Dillwyn), collected from the mid-intertidal zone of a mid-Atlantic salt marsh, were measured under ambient conditions of food, temperature, and salinity over five seasons. Rates of aquatic respiration covaried with body size and season, as the rates were high and strongly related to mussel tissue weight in spring and summer but low and weight independent in winter. There was a significant interannual difference between summer of 1995 and 1996. Rates of aerial respiration also varied seasonally, with high rates of oxygen consumption in summer and low rates in winter. The magnitude of these seasonal variations were greater than those for aquatic respiration, and as a result, the ratio of aerial to aquatic respiration was higher in summer (0.61 and 0.52) than in winter (0.11). This indicates that G. demissa was able to actively regulate aerial respiration, thereby permitting high aerobic metabolism during prolonged periods of air exposure in summer. We hypothesize that such high rates of aerial respiration, during the seasons of high metabolic activity, are required to provide sufficient energy for mussels to facilitate food digestion during air exposure at low tide. Rates of ammonium excretion varied seasonally and increased with mussel weight in all seasons. The atomic ratio of oxygen to nitrogen (O:N), calculated from aquatic respiration vs. ammonium excretion, was significantly lower in autumn (26) than in other seasons (46–60) among which the O:N did not vary significantly.     

Gas Exchange of Algae: II. Effects of Oxygen, Helium, and Argon on the Photosynthesis of Chlorella pyrenoidosa

Changes in the oxygen partial pressure of air over the range of 8 to 258 mm of Hg did not adversely affect the photosynthetic capacity of Chlorella pyrenoidosa. Gas exchange and growth measurements remained constant for 3-week periods and were similar to air controls (oxygen pressure of 160 mm of Hg). Oxygen partial pressures of 532 and 745 mm of Hg had an adverse effect on algal metabolism. Carbon dioxide consumption was 24% lower in the gas mixture containing oxygen at a pressure 532 mm of Hg than in the air control, and the growth rate was slightly reduced. Oxygen at a partial pressure of 745 mm of Hg decreased the photosynthetic rate 39% and the growth rate 37% over the corresponding rates in air. The lowered metabolic rates remained constant during 14 days of measurements, and the effect was reversible after this time. Substitution of helium or argon for the nitrogen in air had no effect on oxygen production, carbon dioxide consumption, or growth rate for 3-week periods. All measurements were made at a total pressure of 760 mm of Hg, and all gas mixtures were enriched with 2% carbon dioxide. Thus, the physiological functioning and reliability of a photosynthetic gas exchanger should not be adversely affected by: (i) oxygen partial pressures ranging from 8 to 258 mm of Hg; (ii) the use of pure oxygen at reduced total pressure (155 to 258 mm of Hg) unless pressure per se affects photosynthesis, or (iii) the inclusion of helium or argon in the gas environment (up to a partial pressure of 595 mm of Hg).