The effects of low pH on the respiration of Daphnia magna Straus.

The effect of low pH values on Daphnia magna is shown to severely depress the O₂ uptake rates. The reason for this is discussed with respect to a decrease in the ability of the gills to exchange CO₂ with the surrounding medium due to a reduction in the CO₂ diffusion gradient as a result of increasing acidity. Respiration in CO₂ free water at acid pH values is shown to be apparently unaffected.     

Effect of food concentration on the respiration of Daphnia magna

The relationship between respiration rate and dry weight forDaphnia magna was investigated in the absence of food. In addition the respiration and feeding rates of matureDaphnia magna females were measured simultaneously at differentChlorella concentrations. It was found that, besides the expected effect of food concentration on the feeding rate, there also was an effect of food concentration on the respiration rate. For food concentrations above a certain critical level a negative correlation between respiration rate and food concentration was found. Below this critical level the effect of the food concentration on the respiration rate was not significant.     

Comment on the position of nitrate respiration in metabolic evolution

This is a reply to Broda's criticism of our concept that nitrate respiration antedated oxygen respiration.     

The effect of prior exposure on sodium uptake in tadpoles exposed to low pH water

Summary Bullfrog tadpoles (Rana catesbeiana) were pre-exposed (7d) to 5 different solutions which varied in ionic composition and pH. Unidirectional sodium influx was then measured over a range of sodium concentrations (50–2000 M) and at 2 pH's (4.0 and 5.8). Tadpoles pre-treated in either distilled water or pH 4.0 soft water exhibited higher sodium influx than animals pre-treated in pH 5.8 soft water. Pre-exposure to solutions high in calcium or sodium reduced sodium influx. Tadpoles pre-treated in pH 4.0 soft water exhibited an increasedV _max for sodium transport, whileK _m was unchanged relative to tadpoles pre-treated in pH 5.8 soft water. In contrast,K _m was increased andV _max was unchanged in tadpoles pre-exposed to high concentrations of calcium or sodium. Within each pre-exposure treatment, influx was inhibited in pH 4.0 test water relative to pH 5.8 test water. However, the magnitude of inhibition was lessened with increasing external concentrations of sodium.Abbreviations ASW artificial soft water - DBM dry body mass - DW distilled water     

Effects of low water potentials on respiration and on glucose and acetate uptake,by Chlorella pyrenoidosa

Summary Chlorella pyrenoidosa was subjected to a range of water potentials and the effects of these treatments on endogenous respiration and on the uptake and respiration of glucose and acetate were measured.For a given water potential the reductions were greatest for glucose, less for acetate, and least for endogenous respiration. At intermediate water potentials of about-10 atm, glucose respiration was depressed strongly at first, but this respiration approached control levels after two to three hours at low water potentials.The reduced respiration of substrates was caused by inhibition of glucose and acetate uptake, as demonstrated by ¹⁴C uptake experiments over short periods. These effects on uptake are attributed to low water potentials, rather than to any possible competition between the molecules of the osmotica and the substrates. Evidence for this view includes the equal inhibitions of glucose-induced respiration by osmotica with such diverse molecular structure as mannitol, KCl, and polyethylene glycol 1540. More conclusively, glucose itself was used as an osmotic agent and its inhibition of glucose-induced respiration was very similar to that by mannitol solutions of equal water potentials.Respiratory activity was much less reduced than uptake. This was demonstrated by lowering the water potential of cells which had already absorbed glucose from a control medium. The subsequent respiration was much higher than that for cells continuously exposed to low water potential.The findings are discussed in relation to the reduced transport of ions and sucrose, which is known to occur in vascular plants subjected to a water stress.The results demonstrate the advantages of using a unicellular organism in the study of metabolic effects of water deficits in plants.     

Effects of water stress on respiration in soybean leaves

The effect of water stress on respiration and mitochondrial electron transport has been studied in soybean (Glycine max) leaves, using the oxygen-isotope-fractionation technique. Treatments with three levels of water stress were applied by irrigation to replace 100%, 50%, and 0% of daily water use by transpiration. The levels of water stress were characterized in terms of light-saturated stomatal conductance (g(s)): well irrigated (g(s) > 0.2 mol H(2)O m(-2) s(-1)), mildly water stressed (g(s) between 0.1 and 0.2 mol H(2)O m(-2) s(-1)), and severely water stressed (g(s) < 0.1 mol H(2)O m(-2) s(-1)). Although net photosynthesis decreased by 40% and 70% under mild and severe water stress, respectively, the total respiratory oxygen uptake (V(t)) was not significantly different at any water-stress level. However, severe water stress caused a significant shift of electrons from the cytochrome to the alternative pathway. The electron partitioning through the alternative pathway increased from 10% to 12% under well-watered or mild water-stress conditions to near 40% under severe water stress. Consequently, the calculated rate of mitochondrial ATP synthesis decreased by 32% under severe water stress. Unlike many other stresses, water stress did not affect the levels of mitochondrial alternative oxidase protein. This suggests a biochemical regulation (other than protein synthesis) that causes this mitochondrial electron shift.     

Benthic faunas of streams of low pH but contrasting water chemistry in New Zealand

Water chemistry and benthic invertebrate communities were investigated at 37 sites on acid streams originating on the Stockton-Denniston Plateau, North Westland, New Zealand. The region is characterised by high rainfall and runoff, highly acidic soils and the presence of extensive coal measures that have been mined for over 120 years. Four groups of streams were identified: naturally acid plateau streams with clear water and very low conductivity; brown water (humic) streams with pH<4 and low conductivity; coastal plains streams with higher pH and conductivity; and streams contaminated by acid mine drainage. TWINSPAN and cluster analysis also grouped streams into four groups based on presence-absence of invertebrate taxa, the groups being similar to, but not identical to those based on physico-chemical factors. Diptera (mainly Chironomidae) were represented by most species in all site groups followed by Plecoptera in plateau streams, and Trichoptera on the coastal plain and where mine drainage occurred. Species of Orthocladiinae (Chironomidae), Plecoptera and Trichoptera were found at the most contaminated sites (pH <3, conductivity >900 µS cm^–1, total reactive aluminium >25 mg 1^–1). The leptophlebiid mayfly Deleatidium was found at 32 of the 37 sites, and some species of Plecoptera, Trichoptera and Chironomidae were also widely distributed. Our findings indicate that species tolerant of low pH (i.e., <4.5) are not confined to humic waters as has been postulated, but also occur in soft, non-humic waters where concentrations of labile, non-organically bound aluminium may be elevated.     

A model for temperature correction of size-specific respiration in Bythotrephes cederstroemi and Daphnia middendorffiana

Respiration rates for the cladocerans Bythotrephes cederstroemi and Daphnia middendorffiana were measured over a broad range of temperatures. The data were fit to the model f(K) W^b where f(°K) is a formulation based on enzyme activity as a function of temperature. The enzyme kinetic model better described the biological observations of respiration as a function of temperature than standard empirical models. The results indicate that Bythotrephes has characteristics of a stenotherm and that the arctic Daphnia middendorffiana has characteristics of a eurytherm based on the linear region of Arrhenius plots (where enzymes are fully active). Above 23°C, Bythotrephes was limited by inactivation of respiratory enzymes. Also, below 14°C, enzyme inactivation became significant and not fully compensated for. Daphnia middendorffiana has a temperature region from 10 to 26°C in which the respiratory process was linear on an Arrhenius plot. Temperature-dependent and weight-specific respiration was described for each species with a formulation over a complete range of environmental temperatures. The formulation for temperature inactivation is applicable to all enzyme processes and should be used in aquatic studies requiring a broad temperature range.      

Tolerance to low ambient calciumshows inter-population differences in Daphnia galeata

The tolerance to low ambient calcium (Ca) was assessed in twopopulations of Daphnia galeata. There was a threshold for survivalbetween 0 and 2 mg Ca l^-1. However, the ability to cope withlow Ca concentrations clearly differed between the two populations,as the population from the low-Ca locality was less tolerantto low Ca. Additionally, neonate individuals had poorer survivalthan adults when reared at ~0 mg Ca l^-1, supporting a suggestedjuvenile bottleneck regarding the tolerance to low Ca concentrations.The mean specific Ca content in adult D. galeata was not differentbetween the two populations, but individuals reared in mediumwith 1 mg Ca l^-1 only had two-thirds of the Ca content of thosereared in medium with 10 mg Ca l^-1. The significant differencesbetween the two populations investigated suggest that inter-populationvariation in tolerance to low ambient Ca concentrations mightbe important to explain the success of Ca-demanding crustaceansin softwater lakes.     

Circulatory oxygen transport in the water flea Daphnia magna

To determine the contribution of circulatory convection to tissue oxygen supply in animals of Daphnia magna, heart rate ( f(H)), in-vivo Hb oxygen-saturation ( S(Hb)) and NADH fluorescence intensity ( I(NADH)) as a measure of the tissue oxygenation state were simultaneously measured using digital motion analysis, microabsorption spectroscopy and fluorescence microscopy. In addition, the relationship between stroke volume and body size was established. Groups of differently sized animals (small: 1.4-1.6 mm, medium: 2.7-2.9 mm, large: 3.3 mm) with either low (Hb-poor) or high Hb concentration (Hb-rich) in the hemolymph were exposed to a gradual decrease in ambient oxygen partial pressure ( P(O2amb)) between normoxia and anoxia. In all groups, f(H) increased in response to progressive hypoxia. The hypoxic maximum in f(H) was highest in medium-sized Hb-poor animals, whereas perfusion rate increased continuously with increasing body size in Hb-poor and Hb-rich animals. The P(O2amb) at which Hb in the heart region was half-saturated (in-vivo P(50)) was higher in medium-sized (Hb-poor: 3.2 kPa, Hb-rich: 2.0 kPa) than in small (Hb-poor: 2.1 kPa, Hb-rich: 1.5 kPa) and large animals (Hb-poor: 1.9 kPa). The in-vivo P(50) was always lower in Hb-rich than in Hb-poor animals. The I(NADH) indicated an impairment of tissue oxygenation starting at higher critical P(O2amb) with increasing body size and with lower Hb concentration. Model calculations suggest that at the respective critical P(O2amb), circulatory convection delivers less than half of the oxygen demand in Hb-poor animals. In contrast, in Hb-rich animals, the contribution of circulatory convection to tissue oxygen supply at respective critical P(O2amb) was much greater due to the higher concentration of Hb.     

Food quality for Daphnia in humic and clear water lakes

1. Growth and reproduction of Daphnia fed lake seston were measured in two categories of meso‐ to eutrophic lakes differing with respect to terrestrial organic matter influence (humic and clear water lakes). The content of highly unsaturated fatty acids (HUFA), P and N, as well as the taxonomical composition of seston were analysed. 2. Seston HUFA and C : P ratios were similar between lake categories, whereas C : N ratios were lower in the clear water lakes in both spring and summer. Despite the similarity in HUFA and P content of seston, Daphnia growth rate, clutch size and the proportion of gravid females were, respectively, about 1.5, 3 and 6 times higher in the clear water lakes. 3. Differences in growth and reproduction were related to a combination of higher N content and good fatty acid quality of the seston in the clear water lakes. Relatively high biomass of edible algae, such as Rhodomonas sp. and Cryptomonas sp., in the clear water lakes, and differences in water pH likely contributed to the observed differences in Daphnia growth and reproduction between lake categories. Additionally, it is possible that Daphnia was energy limited in the humic lakes despite high particulate organic carbon (POC) concentrations, as the contribution of non‐algal and detrital C to the POC pool was high. 4. Our results suggest that dietary HUFA content has the potential to improve herbivore growth and reproduction if N and P are not limiting. N merits more attention in studies of zooplankton nutrition.     

Phenotypic convergence in a natural Daphnia population acclimated to low temperature

Fluidity of a given membrane decreases at lower ambient temperatures, whereas it rises at increasing temperatures, which is achieved through changes in membrane lipid composition. In consistence with homeoviscous adaptation theory, lower temperatures result in increased tissue concentrations of polyunsaturated fatty acids (PUFAs) in Daphnia magna, suggesting a higher PUFA requirement at lower temperatures. However, so far homeoviscous adaptation has been suggested for single or geographically separated Daphnia genotypes only. Here, we investigated changes in relative fatty acid (FA) tissue concentrations in response to a lower temperature (15°C) within a D. magna population. We determined juvenile growth rates (JGR) and FA patterns of 14 genotypes that were grown on Chlamydomonas klinobasis at 15°C and 20°C. We report significant differences of JGR and the relative body content of various FAs between genotypes at either temperature and between temperatures. Based on slopes of reaction norms, we found genotype‐specific changes in FA profiles between temperatures suggesting that genotypes have different strategies to cope with changing temperatures. In a hierarchical clustering analysis, we grouped genotypes according to differences in direction and magnitude of changes in relative FA content, which resulted in three clusters of genotypes following different patterns of changes in FA composition. These patterns suggest a lower importance of the PUFA eicosapentaenoic acid (EPA, C20:5ω3) than previously assumed. We calculated an unsaturation index (UI) as a proxy for membrane fluidity at 15°C, and we neither found significant differences for this UI nor for fitness, measured as JGR, between the three genotype clusters. We conclude that these three genotype clusters represent different physiological solutions to temperature changes by altering the relative share of different FAs, but that their phenotypes converge with respect to membrane fluidity and JGR. These clusters will be subjected to different degrees of PUFA limitation when sharing the same diet.     

The effect of aluminum in soft water at low pH on water balance and hemolymph ionic and acid-base regulation in the dragonflyLibellula julia Uhler

The physiological responses of last instarLibellula julia nymphs exposed for 96 (or 192) h to low pH (4.0 and 2.3) and elevated Al concentrations (0.3, 3, and 30 mg l^–1) at low pH were investigated. To some extent, both low pH alone and Al at low pH were found to affect water balance (wet weight and hemolymph volume), ionic regulation (hemolymph osmolality and concentrations of Na⁺, Cl^–, and K⁺), and acid-base balance (hemolymph pH). The extent and significance of these alterations are discussed.     

Influence of food density on respiration rate of two crustacean plankters,Daphnia galeata and Bosmina longirostris

Summary The influence of food density on respiration rate was measured for two cladoceran plankton species, Daphnia galeata and Bosmina longirostris, over the range 0 to 2.5 mg C 1^-1, using the modified Winkler technique in order to examine how this affects the respiration rate and whether the functional response is the same in the two species. The respiration rate for animals of equivalent body size did not differ significantly between the two species in the absence of food, but was significantly lower in Bosmina longirostris than Daphnia galeata at high food density. Within a species, the response of respiration rate to changing food density did not differ among individuals of different body size. The respiration rate of D. galeata increased with increasing food density and reached a plateau at a high food density. A similar response curve was also found with the respiration rate of B. longirostris, although the response was less conspicuous. This response curve cannot be explained by the energy cost of known feeding behavior in cladocerans. Since the respiration rate related linearly with the assimilation rate, increase in food density seemed to increase the respiration rate by increasing the energetic cost required to process food biochemically, known as specific dynamic action.     

The influence of water stress preconditioning on dark respiration

The respiration rate of individual leaves of cotton (Gossypium hirsutum L. cv. Stoneville 213), beans (Phaseolus vulgaris L. cv. Bush Blue Lake), and sorghum (Sorghum vulgare Pers.) which had been fully expanded prior to a series of severe water stresses was compared with those of unstressed leaves of similar age. Measurements were made over a range of leaf temperatures. The respiration rate per unit area of the leaves of all rewatered plants were significantly lower than those of the plants which had not undergone water stress. During the stress periods, the leaves of all species suffered dry matter loss. The respiration rates per unit dry matter for cotton and beans were the same for the plants which had undergone stress as they were for the plants which had not undergone stress, thus for these two C3 plants the decrease in dark respiration due to water stress may be explained entirely by the loss of dry matter. Respiration rates of the water stressed sorghum leaves expressed on a per unit weight basis were significantly lower than those which had not undergone water stress preconditioning. The lower respiration rates of the stressed leaves when expressed on both a per unit area basis and a per unit weight basis for the C4 species indicate that water stress adaptation of C4 plants may include alterations in the respiratory mechanism or on the amount of residual respirable substrate. The light compensation points of all the species were not altered by the water stress preconditioning. This indicates that the mechanisms controlling the net photosynthetic exchange per unit leaf area underwent adaptations as a result of repeated water stress which decreased its efficiency.     

Some aspects of respiration and respiration inhibitors in low temperature effects of the cotton plant

Respiration of leaf tissue from cotlon plants in the nine leaf stage was found to be severely reduced at temperatures below 15°C. In another study, young cotton plants were exposed to chilling temperature (2.8°C) for 72 hours and the ability of the plant tissues to recover respiration at normal temperatures (15 and 25°C) was examined at periodic intervals. Chilling exposures of 12 hours injured cotton tissues as indicated by increased respiratiou of leaves and roots at 25°C. Further chilling malerially reduced the capacity of the leaves to re-estahlish normal respiration rales at higher temperatures. Picolinic acid, Dexon and matonate were used to study the influence of respiratory inhibitors on the chill damage of the collon plants. The chemicals were applied six hours before cold exposure aud fhe growth and development of cold injured plants was studied to indicate the effectiveness of the treatments. Tissue weights at the final harvests indicated that picolinic acid and Dexon treated plants recovered better after cold injury than the untreated plauts. The results suggest thai 15°C may be a critical temperaliire for many physiological processes of the cotton plant because the supply of energy needed for plant reactionsis restricted due to inadequate respiration. They also indicate that the disturhances in respiration are among the early effects of chilling colton plants and may be the cause of delayed growth and development of cotton plants subjccled to non-lethal chilling exposures. It is concluded that chemicals like picolinie acid and Dexon may he effective through protection of specific systems rather than a general reduction of respiration.