Dark Oxygen Uptake Research Articles

A biogeochemical survey of the anoxic basin Golfo Dulce, Costa Rica

The waters and surface sediments of a 200 m deep tropical fjord were investigated with respect to chemical zonation, rates of respiratory processes. and benthic fluxes. Oxygen was found to ca. 100 m water depth. but only the upper pan of the oxycline was associated with the pycnocline. which was situated above the sill located at 60 m. Nitrate-rich water entered the bay at sill depth, and denitrification was indicated at anoxic depths. Hydrogen sulfide was only found in low concentrations near the bottom, and nitrate was a possible oxidant for the hydrogen sulfide. The observations reproduced those of a survey in 1969 to a large extent. This suggests that water exchange is frequent enough to prevent the development of strongly reducing conditions in the bottom water, High rates of dark oxygen uptake indicated intense carbon cycling within the euphotic zone. The rates decreased rapidly with depth, and at anoxic depths, rates of denitrification and sulfate reduction were more than 100-fold lower than the surface oxygen uptake. The chemical zonation as well as x-radiographs indicated that sediments underlying oxic bottom water were strongly irrigated and bioturbated while anoxic sediments were laminated and composed of turbidites. The rates of carbon oxidation were 5-10 times higher in the sediments underlying oxic bottom water than in those of the bottom of the basin. Sulfate reduction was a dominating process. accounting for about 50% and 100% of the carbon oxidation at the oxic and anoxic sites respectively. Even at the anoxic sites, hydrogen sulfide did not accumulate in the pore Waler and a high sedimentation of reactive iron phases is suggested as a contributing cause.

Anemonefish oxygenate their anemone hosts at night

Many stony coral-dwelling fishes exhibit adaptations to deal with hypoxia among the branches of their hosts; however, no information exists on the respiratory ecophysiology of obligate fish associates of non-coral organisms such as sea anemones and sponges. This study investigated metabolic and behavioral interactions between two-band anemonefish (Amphiprion bicinctus) and bulb-tentacle sea anemones (Entacmaea quadricolor) at night. We measured the net dark oxygen uptake ( , μmol O2 h(-1)) of fish-anemone pairs when partners were separate from each other, together as a unit, and together as a unit but separated by a mesh screen that prevented physical contact. We also measured the effects of water current on sea anemone and quantified the nocturnal behaviors of fish in the absence and presence of host anemones in order to discern the impacts of anemone presence on fish behavior. Net of united pairs was significantly higher than that of both separated pairs and united pairs that were separated by a mesh screen. Anemone increased with flow rate from 0.5 to 2.0 cm s(-1), after which remained constant up to a water flow rate of 8.0 cm s(-1). Furthermore, the percentage time and bout frequency of flow-modulating behaviors by fish increased significantly when anemones were present. We conclude that physical contact between anemonefish and sea anemones elevates the of at least one of the partners at night, and anemonefish behavior at night appears to oxygenate sea anemone hosts and to augment the metabolism of both partners.

EFFECT OF SALICYLIC ACID ON PHOTOSYNTHESIS AND SOME ANTIOXIDANT ENZYMES OF STRESSED SCENEDESMUS OBLIQUUS CULTURES

This study followed the effect of salicylic acid on growth criteria, photosynthetic pigments, photosynthesis, respiration, proline and the activities of some antioxidant enzymes of stressed Scenedesmus obliquus cultured for 7 days. The growth criteria (cell number and dry weight) and total pigments ofnon- stressed and stressed Scenedesmus obliquus cultures were significantly increased, when the algal cultures were subjected to 200 mM NaCl and treated with 100and 200 ppm of salicylic acid. Also, Photosynthesis (oxygen evolution), respiration (dark oxygen uptake), proline, amino acids and catalase enzyme of non- salinized and salinized Scenedesmus obliquus cultured were significantly increased, when the algal cultures were subjected to 200 mM NaCl and treated with 100and 200 ppm of salicylic acid. However, both respiration (oxygen uptake) , lipid peroxidation as termed (malondialdhyde) and peroxidase were significantly decreased, when the algal cultures were subjected to 200 mM NaCl and treated with 400 ppm of salicylic. These values were compared with that of the control cultures.

Impacts of longline mussel farming on oxygen and nitrogen dynamics and biological communities of coastal sediments

Benthic communities and benthic mineralization were studied in two shallow coastal regions of New Zealand: Tasman Bay, a possible future site for mussel farm development, and Beatrix Bay, which already hosts several longline mussel farms. In Tasman Bay, microphytobenthic (MPB) production added significantly to the total primary production of the bay. The activity of benthic microalgae had a pronounced effect on oxic conditions, solute exchange and denitrification rates. Benthic mineralization, quantified as the dark oxygen uptake, was in the range of 675±11 μmol m −2 h −1. Denitrification rates were high and fueled entirely by nitrate produced by the nitrifying community within the sediment. Competition for inorganic nitrogen between benthic microalgae and nitrifiers/denitrifiers resulted in diel variation in nitrogen cycling and reduced the inorganic nitrogen efflux and denitrification activity in the light. Calculated in electron equivalents, denitrification accounted for 11–20% of the total carbon mineralization—one of the highest numbers reported for coastal sediments. Reduced sediments, containing low MPB biomass and few subsurface macroinvertebrate species, were observed below a mussel farm in Beatrix Bay, presumably due to the intensified sedimentation of organic matter. Oxygen consumption increased in the organic-rich sediments, and ammonium effluxes were up to 14 times higher than those of unaffected sediments 250 m away from the farm. Denitrification rates below the farm were low as the coupled nitrification–denitrification was inhibited by the presence of sulfide. The dissimilative reduction of nitrate to ammonium (DRNA) was, however, stimulated in the reduced sediment. The enhanced benthic mineralization was associated with sulfidic sediments and a lower nitrogen removal rate due to impeded benthic photosynthesis and denitrification activity. The described local conditions associated with mussel farming should be taken into account when new areas are considered for development.

Factors affecting microphytobenthic biomass, species composition and production in the Colne Estuary (UK)

Biomass, species composition and primary production of the microphytobenthos (MPB) were investigated along environmental gradients in the Colne Estuary between August 1996 and March 1998. Mean monthly sediment chlorophyll a (chl a) concentrations varied between 6 and 241 mg m -2 . There was no seasonal pattern in chl a distribution. Low chl a concentrations were asso- ciated with the estuary mouth, which was characterised by exposed sandy sediments and low water column nutrient concentrations. Position on the shore affected biomass, with greater chl a concentra- tions on the high shore. Chl a concentrations followed the same pattern at both high and low shore positions. There was a significant relationship between concentrations of sediment colloidal carbo- hydrate and chl a. Epipelic diatoms dominated the MPB, with cluster analysis identifying 10 distinct species assemblages. Navicula spp. were an important component of all assemblages. Peaks in chl a biomass occurred when a single species made up >65% of the cell numbers. The distribution of the diatom assemblages was related to salinity, temperature and dissolved inorganic nitrogen (DIN) con- centrations. Net production of oxygen occurred in sediments under illumination at all sites on almost all occasions. Oxygen uptake by sediment in the dark was positively correlated with temperature at the head of the estuary, but not at any other site. Mean annual chl a concentrations correlated posi- tively with total annual dark oxygen uptake. Annual primary production was estimated by 4 models using chl a concentrations and a model based on gross O2 fluxes across the sediment-water interface. Production was estimated to be in the range of 25 to 1199 gC m -2 yr -1 , depending on site and model. There was greater production on the high shore than on the low shore, due to higher chl a concen- trations and longer emersion periods. Total production of MPB in the estuary was estimated to be between 117 and 852 tons C yr -1 . Assimilation by the MPB provided a temporary sink for DIN, equiv- alent to 12.8% of the annual 1996 load to the Colne Estuary. N assimilation rates by the MPB were in the same order of magnitude as denitrification, indicating that assimilation by the MPB is an impor- tant process affecting the flux of DIN through this mesotidal estuary.

Seasonal organic mineralisation and denitrification in intertidal sediments and their relationship to the abundance of Enteromorpha sp. and Ulva sp.

Sedimentary organic matter mineralisation (oxygen uptake), nitrogen (N) loss (denitrification) and nutrient exchange were measured seasonally in areas of both high and low Enteromorpha sp. and Ulva sp. cover at 6 sites in 2 harbours on the south coast of England. Measurements of macroalgal and phytoplankton photosynthesis were also carried out. Sedimentary carbon (C) and N cycling was most rapid at the sites with a heavy cover of macroalgae. Macroalgae were responsible, on average, for 57% of total dark oxygen uptake, with sediment bacterial respiration accounting for the remaining 43 %. Dark rates of nutrient uptake for Enteromorpha sp. and Ulva sp. were equivalent to 70% of those in the light. Denitrification rates were low (D w [NO 3 - from overlying water] 98%) remained within the system. External inputs of nutrients (N and P) to the harbours may have supported the spring growth of macroalgae, but it seemed unlikely that they were capable of supporting the summer peaks in algal biomass and rapid rates of N turnover. More likely the intense recycling (ammonification) of organically bound N within the sediments, coupled to a minimum loss via denitrification, provided a sustained and sufficient N supply for the macroalgae.

Effects of prolonged drought stress and nitrogen deficiency on the respiratory O2 uptake of bean and pepper leaves

We analyzed the combined effects of mild drought stress and severe nitrogen (N) deprivation on respiration of acclimated mature leaves of beans (Phaseolus vulgaris L. cv. Garrofal) and peppers (Capsicum annuum L., pure line B6). Rates of oxygen uptake were measured polarographically, and inhibitors were added to the closed cuvette to compare the effects of environmental stress on the cytochrome (cyt) and alternative pathways of mitochondrial respiration. Dark oxygen uptake was decreased by the water deficit treatment in both plants, and in the case of N limitation leaf respiration rates (RD) of peppers were also reduced. RD of leaves of beans and peppers grown under N-limiting conditions did not follow the decrease in leaf N concentration, since RD expressed per unit of tissue N was considerably higher in the N-stressed leaves. Values obtained with specific inhibitors of the two terminal oxidases of mitochondrial respirations suggested that the cyt pathway of respiration was affected by mild drought and severe N stress. When plants were exposed to both environmental stresses, leaf respiration response was similar to that under N limitation, in this case the most severe stress.

Acclimation of Respiratory O2 Uptake in Green Tissues of Field-Grown Native Species after Long-Term Exposure to Elevated Atmospheric CO2.

C3 and C4 plants were grown in open-top chambers in the field at two CO2 concentrations, normal ambient (ambient) and normal ambient + 340 [mu]LL-1 (elevated). Dark oxygen uptake was measured in leaves and stems using a liquid-phase Clark-type oxygen electrode. High CO2 treatment decreased dark oxygen uptake in stems of Scirpus olneyi (C3) and leaves of Lindera benzoin (C3) expressed on either a dry weight or area basis. Respiration of Spartina patens (C4) leaves was unaffected by CO2 treatment. Leaf dry weight per unit area was unchanged by CO2, but respiration per unit of carbon or per unit of nitrogen was decreased in the C3 species grown at high CO2. The component of respiration in stems of S. olneyi and leaves of L. benzoin primarily affected by long-term exposure to the elevated CO2 treatment was the activity of the cytochrome pathway. Elevated CO2 had no effect on activity and capacity of the alternative pathway in S. olneyi. The cytochrome c oxidase activity, assayed in a cell-free extract, was strongly decreased by growth at high CO2 in stems of S. olneyi but it was unaffected in S. patens leaves. The activity of cytochrome c oxidase and complex III extracted from mature leaves of L. benzoin was also decreased after one growing season of plant exposure to elevated CO2 concentration. These results show that in some C3 species respiration will be reduced when plants are grown in elevated atmospheric CO2. The possible physiological causes and implications of these effects are discussed.

In situ bacterial production and growth yield measured by thymidine, leucine and fractionated dark oxygen uptake

<i>In situ</i> bacterial production and growth yield measured by thymidine, leucine and fractionated dark oxygen uptake

Regulation of Mitochondrial Function and Biogenesis in Cucumber (Cucumis sativus L.) Cotyledons during Early Seedling Growth

The aim of this work was to characterize the respiratory metabolism of the greening cotyledons of cucumber (Cucumis sativus L.) during early seedling growth and to investigate how this is integrated with changes in mitochondrial biogenesis and function. In light-grown cotyledons, lipid mobilization extended from germination to 6 days postimbibition, reaching a maximum at 3 to 4 days postimbibition. The rate of dark oxygen uptake reached a maximum at 2 days postimbibition in dark-grown and 3 days postimbibition in light-grown cotyledons. Development of photosynthetic capacity occurred from 4 to 7 days postimbibition. In dark-grown cotyledons, lipid mobilization extended beyond 7 days postimbibition, and there was no greening or acquisition of photosynthetic competence. Measurements of mitochondrial function indicated that the respiratory capacity of the tissue changed such that during lipid mobilization there was a much greater capacity for the operation of the nondecarboxylating portion of the citric acid cycle (succinate to oxaloacetate), whereas during the development of photosynthetic function the activity of the remainder of the cycle (oxaloacetate to succinate) was induced. Comparison of the maximum capacities for mitochondrial substrate oxidations in vitro with the rates of in vivo substrate oxidations, predicted from the rate of lipid breakdown, indicated that mitochondria in this tissue operate at or below state 4 rates, suggesting limitation by both availability of ADP and substrate.

Effect of Na-Ca Combinations on Photosynthesis and some Related Processes of Chlorella Vulgaris

Summary The physiological responses of Chlorella vulgaris to various NaCl levels and Na-Ca combinations were followed. Cell number, dry weight, photosynthetic pigments (chlorophyll a and chlorophyll b), photosynthetic oxygen evolution, respiration (dark oxygen uptake), the content of free amino acids and proline were investigated. With the rise of the NaCl level, growth was retarded. Inclusion of Ca 2+ in the media enhanced the growth of salinized cultures. The maxima of cell number, dry matter and pigments were recorded under a Na + /Ca 2+ ratio of 13.5. The photosynthetic oxygen evolution was generally inhibited by NaCl. The partial substitution of Ca 2+ for Na + improved photosynthetic oxygen evolution. Respiration was enhanced with the rise of the salinization level. Minimal respiration rates of variously treated Chlorella cultures also occured under a Na + /Ca 2+ ratio of 13.5. Proline accumulation was markedly enhanced in variously treated cultures, but under a Na+/Ca2+ ratio of 13.5 proline accumulation was retarded. Therefore the Na+/Ca2+ ratio of 13.5 could be regarded as the optimal ratio for growth of stressed Chlorella vulgaris cultures.

Photosynthetic and respiratory oxygen gas exchange measured by mass spectrometry in the filamentous cyanobacterium Oscillatoria chalybea in dependence on the nitrogen source in the growth medium

Thylakoid particle preparations of the filamentous cyanobacterium Oscillatoria chalybea were prepared from cultures that were grown on nitrate, ammonium sulfate or arginine as the sole nitrogen source in the medium. Moreover, cultures that had no exogenous nitrogen source in the medium, hence used air as nitrogen source, were also grown. Oxygen gas exchange of these preparations was analyzed by means of mass spectrometry in an assay system that contained in the liquid phase only H216O-containing buffer (hence no H218O label) and air as gas phasein which part of the 16O2 had been substituted by 18O2. Oxygen uptake in the dark was very low in all preparations but reacted in a subtle way already to very dim (less than 10 lx) illumination. In preparations of nitrate- and ammonium sulfate-grown cultures the dark-uptake rate was enhanced in dim light and appeared further enhanced in the dark period following this illumination. In preparations of arginine-grown cells or cells without nitrogen source in the medium dim light inhibited dark oxygen uptake. In weak light (80 lx) none of the preparations showed an O2-uptake phenomenon but rather an 02-evolution phenomenon. Both mass signals (mass 32 and mass 36) indicated O2 evolution. No mixed label 16O18O was found indicating that 18O2 evolved cannot come from water produced by respiratory activity for instance, but should come from H2O2. Only in strong saturating light (2 · 104 lx white light) an appreciable l8O2-uptake was observed. This uptake was sensitive to DCMU, o-phenanthroline, the uncoupler CCCP, KCN and SHAM. The uncoupler CCCP stimulated 18O2 uptake in strong light, but also affected as an ADRY-reagent photosynthetic oxygen evolution. CCCP abolished also the 1802-evolution signal in weak light (80 lx) demonstrating that the S-state system is involved in 18O2 production from H2O2. KCN also abolishes the weak light 18O2 evolution and inhibits 18O2 uptake in strong light. It appears that the low light intensity signal, also when measured as flash-induced signal, is inverted by KCN to an uptake phenomenon which, when analyzed under flash light, exhibits a periodicity of 2. It is suggested that part of the KCN effect observed with such preparations is due to an effect on cytochrome b-559. The effect of SHAM on oxygen uptake in strong light seems to indicate that O.chalybea owns in addition a CN−-insensitive respiratory pathway. Hence, in O. chalybea our method permits the distinction of at least three types of oxygen uptake: one is associated with Photosystem II and the S-state system, whereas the two other types apparently belong to the respiratory pathway.

Substrate Restriction in Entomophilous Splachnaceae: II. Effects of Hydrogen Ion Concentration on Establishment of Gametophytes

The authors tested the hypothesis that establishment of Splachnum gametophytes is limited to neutral substrates by examining the effect of hydrogen ion concentration on spore germination, protonemal growth, and gametophore production in Splachnum ampullaceum, S. luteum, and S. sphaericum. Decreased germination was observed in S. sphaericum spores grown at pH 4 as compared to pH 7. Splachnum ampullaceum and S. luteum, however, exhibited no spore germination response to pH. Protonemal growth and gametophore production were inhibited at pH 4 compared to pH 7 in all taxa. Numbers of cells and protonemal branches per filament, chlorophyll a content, and total protein content were significantly reduced at pH 4. In addition, dark oxygen uptake was higher and light-dependent oxygen evolution was lower in protonema of S. ampullaceum grown at pH 4. In vivo ({sup 35}S) sulfate-labelled protonema of S. ampullaceum grown at pH 4 and pH 7 produced generally similar polypeptide patterns on one-dimensional polyacrylamide gels, but four major differences were detected. Total ({sup 35}S) sulfate uptake and incorporation into protein were reduced in protonema grown at pH 4. These observations are consistent with the neutrophilic hypothesis of substrate restriction in Splachnum.

Assessing photosynthetic oxygen liberation using a BBC microcomputer

Photosynthetic oxygen liberation is measured in cultures of green and blue-green algae using a BBC microcomputer. A program is described which can take readings from an oxygen electrode (which holds a culture sample) and a photocell simultaneously. The readings are displayed graphically on a monitor and printed out immediately, for periods of up to 24 hours and longer, with constant temperatures. Results obtained clearly demonstrate the effect of light as a limiting factor. From printed data of longer running experiments it has been possible to identify the precise time during the early morning when net oxygen output first occurred. From such data the extent of dark respiratory oxygen uptake and consequently the difference between true and apparent photosynthetic oxygen liberation in the light have also been deduced. Cultures of blue-green algae have considerable photorespiratory activity but show lower rates of oxygen uptake in the dark compared with green algae.

A comparison of the photosynthesis — light intensity relationship in phylogenetically different marine microalgae

Measured under equivalent physiological conditions, the photosynthesis-light intensity relationship based on oxygen production/mg chlorophyll a was found to be the same in five species representing the different chlorophyll c containing divisions of marine phytoplankton. Other non-photochemical metabolic processes related to photosynthesis such as diurnal variations, maximal photosynthesis rates, and dark oxygen uptake were quite different, and so these are the more significant factors in production and ecological distribution of diatoms, dinoflagellates, and coccolithophores. In contrast, the green algae tested showed a significantly different photosynthesis-light intensity curve from the chlorophyll c group.

Respiration in cell development.

Dark oxygen uptake was measured manometrically for cells of green high-temperature alga, Chlorella 7-11-05, separated from nonsynchronized populations by centrifugation into fractions of predominantly small or large cells. In the presence of exogenous glucose, respiration activity of the smaller (younger) cell fraction was invariably higher than that of the larger (older) cell fraction. In the absence of exogenous substrate, the difference in respiration rates in two fractions of cells was inconsistent from one experiment to another both in size and in sign. The dependence of dark respiration on the amount of available substrate makes the endogenous respiration rate unsuitable as an indicator of the inherent capacity of respiratory mechanisms. In observations on synchronized heterotrophically grown cells, the glucose respiration rate expressed per dry weight of cells gradually declined over the developmental period irrespective of the adequate exogenous supply of glucose or illumination by weak light. Observations on synchronized heterotrophically grown Chlorella cells thus corroborated studies of glucose respiration in cells separated into are groups by centrifugation. The decline in metabolic activity in the course of cell development previously established for growth and photosynthesis extends to include respiration activity. Disagreements among several investigators in regard to the course of respiration during cell development are probably due to the effects of accessory factors such as strong light during the preceding growth period or the scarcity of respiratory substrate during respiration measurements which affect and distort changes in the inherent capacity of metabolic mechanisms in the course of cell development.

Effects of phosphorus and sulphur on dark respiration of subterranean clover leaves

Respiration rates in the dark (oxygen uptake) of leaves sampled from subterranean clover plants (Trifolium subterraneum L. cv. Mt Barker) increased with the phosphorus supply in the culture solutions in which the plants were grown. Over a period of 3 hr no differences were detected in respiration rates when leaves of these plants were placed in Warburg flasks containing complete solutions or solutions without phosphorus. However, when whole plants were transferred to complete and no-phosphorus solutions, the differences in respiration rates of leaves sampled from the two groups of plants depended on the phosphorus status of the plants at transfer. Leaves from plants raised at an adequate phosphorus level showed no differences over a period of 96 hr after transfer, but leaves from plants raised at suboptimal phosphorus levels before transfer to complete and no-phosphorus solutions showed significant differences in respiration rates as early as 18-19 hr after transfer. Similar results were obtained for leaves sampled from plants raised at different sulphur levels when transferred to complete solutions and to solutions without sulphur. However, these differences took longer to develop than in the phosphorus experiments. When phosphorus-deficient plants were transferred to complete solutions and to other solutions each without a different element, the respiration rates of the leaves sampled from the plants in the solutions without phosphorus were much lower than for the leaves of plants in the other solutions.

The Effeots of the Dipyridyl Diquat on the Metabolism of Chlorella Vulgaris I. Gas Exchange in the Light

The effects of diquat on gas exchange in illuminated C. vUlgaris have been studied by manometric procedures. Estimates of dark oxygen uptake were made by transfer of treated cells to darkness. Analysis of the results indicates that on adding diquat to C. vUlgariB there is a rapid fall in the rate of apparent photosynthesis. This is due to an immediate and large increase in dark metabolism (C02 and O2 exchange) accompanied by irreversible inhibition of real photosynthesis firstly, then of respiration. At some unspecified stage a light-dependent oxygen uptake begins, rises to a maximum rate, and declines to a low value, continuing after the inhibition of respiration. These results are discussed in relation to the known effects of diquat on plastid reactions and to the hypothesis that in illuminated green tissue diquat produces a toxic substance which damages both the photosynthetic and respiratory apparatus.