The Influence of Salinity on the Rate of Dark Respiration and Structure of the Cells of Brown Algae Thalli from the Barents Sea Littoral

We studied the changes in the rate of dark respiration (DR) and structure of the cells in Ascophyllum nodosum and Fucus vesiculosus thalli during the incubation at 40, 34, 20, 10, and 2 salinity for 14 days. The changes in salinity affected the rate of DR and the structure of the thallus apical cells: the organelles swollen and were destroyed later. The effect of hyposalinity on the algae was more pronounced as compared to hypersalinity. The stress intensity directly increased with the degree of desalination. Further adaptation of the algae to low salinity enhanced DR and, hence, was an energy-dependent process. Despite higher DR rates (during the stress and adaptation) in F. vesiculosus as compared to A. nodosum, the seaweeds had similar pattern of adaptation to the variation of salinity. Different primary response of the seaweeds to 20 salinity was an important exception; apparently, the salinity around 20 is the limit of these species distribution in desalination zones.     

Effect of dissolved inorganic carbon on oxygen evolution and uptake by Chlamydomonas reinhardtii suspensions adapted to ambient and CO2-enriched air

Mass spectrometric measurements of ¹⁶O₂ and ¹⁸O₂ isotopes were used to compare the rates of gross O₂ evolution (E₀), O₂ uptake (U₀) and net O₂ evolution (NET) in relation to different concentrations of dissolved inorganic carbon (DIC) by Chlamydomonas reinhardtii cells grown in air (air-grown), in air enriched with 5% CO₂ (CO₂-grown) and by cells grown in 5% CO₂ and then adapted to air for 6h (air-adapted).At a photon fluence rate (PFR) saturating for photosynthesis (700 mol photons m^-2 s^-1), pH=7.0 and 28°C, U₀ equalled E₀ at the DIC compensation point which was 10M DIC for CO₂-grown and zero for air-grown cells. Both E₀ and U₀ were strongly dependent on DIC and reached DIC saturation at 480 M and 70 M for CO₂-grown and air-grown algae respectively. U₀ increased from DIC compensation to DIC saturation. The U₀ values were about 40 (CO₂-grown), 165 (air-adapted) and 60 mol O₂ mg Chl^-1 h^-1 (air-grown). Above DIC compensation the U₀/E₀ ratios of air-adapted and air-grown algae were always higher than those of CO₂-grown cells. These differences in O₂ exchange between CO₂- and air-grown algae seem to be inducable since air-adapted algae respond similarly to air-grown cells.For all algae, the rates of dark respiratory O₂ uptake measured 5 min after darkening were considerably lower than the rates of O₂ uptake just before darkening. The contribution of dark respiration, photorespiration and the Mehler reaction to U₀ is discussed and the energy requirement of the inducable CO₂/HCO₃ ^- concentrating mechanism present in air-adapted and air-grown C. reinhardtii cells is considered.Abbreviations DIC dissolved inorganic carbon - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - E₀ rate of photosynthetic gross O₂ evolution - PCO photosynthetic carbon oxidation - PFR photon fluence rate - PS I photosystem I - PS II photosystem II - U₀ rate of O₂ uptake in the light - MS mass spectrometer     

16O2/18O2 analysis of oxygen exchange in Dunaliella tertiolecta. Evidence for the inhibition of mitochondrial respiration in the light

A mass spectrometric ¹⁶O₂/¹⁸O₂-isotope technique was used to analyse the rates of gross O₂ evolution, net O₂ evolution and gross O₂ uptake in relation to photon fluence rate by Dunaliella tertiolecta adapted to 0.5, 1.0, 1.5, 2.0 and 2.5 M NaCl at 25°C and pH 7.0.At concentrations of dissolved inorganic carbon saturating for photosynthesis (200 M) gross O₂ evolution and net O₂ evolution increased with increasing salinity as well as with photon fluence rate. Light compensation was also enhanced with increased salinities. Light saturation of net O₂ evolution was reached at about 1000 mol m^-2s^-1 for all salt concentrations tested. Gross O₂ uptake in the light was increased in relation to the NaCl concentration but it was decreased with increasing photon fluence rate for almost all salinities, although an enhanced flow of light generated electrons was simultaneously observed. In addition, a comparison between gross O₂ uptake at 1000 mol photons m^-2s^-1, dark respiration before illumination and immediately after darkening of each experiment showed that gross O₂ uptake in the light paralleled but was lower than mitochondrial O₂ consumption in the dark.From these results it is suggested that O₂ uptake by Dunaliella tertiolecta in the light is mainly influenced by mitochondrial O₂ uptake. Therefore, it appears that the light dependent inhibition of gross O₂ uptake is caused by a reduction in mitochondrial O₂ consumption by light.Abbreviations DCMU 3-(3, 4-dichlorophenyl)-1, 1-dimethylurea - DHAP dihydroxy-acetonephosphate - DIC dissolved inorganic carbon - DR_a rate of dark respiration immediately after illumination - DR_b rate of dark respiration before illumination - E₀ rate of gross oxygen evolution in the light - NET rate of net oxygen evolution in the light - PFR photon fluence rate - RubP rubulose-1,5-bisphosphate - SHAM salicyl hydroxamic acid - U₀ rate of gross oxygen uptake in the light     

Interactions of glycolate-, HCO 3 - -, Cl--, and H+-balance of Scenedesmus obliquus

Excretion and absorption of glycolate by young cells of Scenedesmus obliquus (Turp.) Krüger strain D₃ grown synchronously with 2% CO₂ was compared after no pretreatment with air (CO₂-adapted) or after a 2 h adaptation to normal air (0.03% CO₂) (air-adapted). At 21% O₂, excretion occurred only from CO₂-adapted cells at high pH (pH 8.0). Under conditions where no excretion occurred, external glycolate (0.2 mM) was taken up by both air-and CO₂-adapted cells at a much faster rate at pH 5 than at pH 8. The uptake was accompanied by an apparent stoichiometric uptake of H⁺. CO₂-adapted algae exhibited high uptake rates that were even higher in the dark than in the light. Air-adapted algae showed high uptake rates in the light but only minimal uptake in the dark. The uptake rate was decreased to about 1/3 with 5% CO₂, except with CO₂-adapted cells in the light, in which a slight stimulation occurred. Cl^- ions inhibited glycolate uptake by air-adapted cells in the light; conversely, light-stimulated Cl^- uptake of these cells was inhibited by glycolate. A hypothesis is discussed according to which the internal pH regulates the uptake and release of Cl^-, HCO ₃ ^- , and glycolate.Abbreviations DCMU 3-(3,4 dichlorophenyl)-1, 1-dimethyl urea - FCCP carbonyl cyanide p-trifluoro-methoxyphenylhydrazone - HEPES 2-(4-(2-hydroxyethyl)-piperazinyl) ethanesulfonic acid - HPMS -hydroxypyridinemethanesulfonate - MES 2-morpholinoethanesulfonic acid - PCV packed cell volume     

Photosynthetic gas exchange under emersed conditions in eulittoral and normally submersed members of the Fucales and the Laminariales: interpretation in relation to C isotope ratio and N and water use efficiency

Summary Ten species of brown macroalgae (five eulittoral and one submersed species of the Fucales; four submersed species of the Laminariales) from a rocky shore at Arbroath, Scotland, were examined for characteristics of emersed photosynthesis in relation to the partial pressure of CO₂ and O₂. The five eulittoral species of the Fucaceae were approaching CO₂ saturation for light-saturated photosynthesis at normal air levels of CO₂ (35 Pa) in 21 kPa O₂. The normally submersed algae are further from CO₂ saturation under these conditions, especially in the case of the four members of the Laminariales. The rate of net photosynthesis in the Fucaceae is O₂-independent in the range 2–21 kPa O₂ over the entire range of CO₂ partial pressure tested (compensation up to 95 Pa). For the other five algae tested, net photosynthesis is slightly inhibited by O₂ at 21 kPa relative to 2 kPa over the entire range of CO₂ partial pressures tested (compensation up to 95 Pa). CO₂ compensation partial pressures are low (<0.5 Pa) for the Fucaceae and independent of O₂ in the range 2–42 kPa. For the other five algae, the CO₂ compensation partial pressure are higher, and increased with O₂ partial pressure in the range 2–42 kPa. These gas exchange data show that the Fucaceae exhibit more C₄-like characteristics of their photosynthetic physiology than do the other five species tested, although even the Laminariales and Halidrys siliquosa are not classic C₃ plants in their photosynthetic physiology. These data suggest that, in emersed conditions as well as in the previously reported work on submersed photosynthesis, a CO₂ concentrating mechanism is operating which, by energized transmembrane transport of inorganic C, accumulates CO₂ at the site of RUBISCO and, at least in part, suppresses the oxygenase activity. Work with added extracellular carbonic anhydrase (CA), and with a relatively membrane-impermeant inhibitor of the native extracellular CA activity (acetazolamide), suggests that, in emersed conditions as well as in the previously reported work on algae submersed in seawater at pH 8, HCO _inf3 ^sup– is the major inorganic C species entering the cell. At optimal hydration, the rate of emersed photosynthesis in air is not less than the rate of photosynthesis when submersed in seawater, at least for the Fucaceae. ¹³C ratios of organic C for the Fucaceae are slightly more negative than is the case for the other five algae; these data are consitent with substantial (half or more of the entering inorganic C) leakage of CO₂ from the accumulated pool, and with some contribution of atmospheric CO₂ to the organic C gain by the eulittoral algae. The predicted increase in N use efficiency of photosynthesis in the Fucaceae, with their more strongly developed CO₂ concentrating mechanism, is consistent with data on emersed, but not submersed, photosynthesis for the algae collected from the wild and thus at a poorly defined N status. The more C₄-like gas exchange charateristics of photosynthesis in the eulittoral Fucaceae may be important in increasing the water use efficiency of emersed photosynthesis from the limited capital of water available for transpiration by a haptophyte.     

Photosynthetic inorganic carbon utilization and growth of Porphyra linearis (Rhodophyta)

Photosynthetic (oxygen evolution) and growth (biomass increase) responses to ambient pH and inorganic carbon (Ci) supply were determined for Porphyralinearis grown in 0.5 L glass cylinders in the laboratory, or in 40 L fibreglass outdoor tanks with running seawater. While net photosynthetic rates were uniform at pH 6.0–8.0, dropping only at pH 8.7, growth rates were significantly affected by pH levels other than that of seawater (c. pH 8.3). In glass cylinders, weekly growth rates averaged 76% at external pH 8.0, 13% at pH 8.7 and 26% at pH 7.0. Photosynthetic O₂ evolution on a daily basis(i.e. total O₂ evolved during day time less total O₂ consumed during night time) was similar to the growth responses at all experimental pH levels, apparently due to high dark respiration rates measured at acidic pH. Weekly growth rates averaged 53% in algae grown in fibreglass tanks aerated with regular air (360 mg L_-1 CO₂) and 28% in algae grown in tanks aerated with CO₂-enriched air (750 mg L^-1 CO₂). The pH of the seawater medium in which P. linear is was grown increased slightly during the day and only rarely reached 9.0. The pH at the boundary layer of algae submerged in seawater increased in response to light reaching, about pH 8.9 within minutes, or remained unchanged for algae submerged in a CO₂-free artificial sea water medium. Photosynthesis of P. linearissaturated at Ci concentrations of seawater (K_0.5560 μM at pH 8.2) and showed low photosynthetic affinity for CO₂(K_0.5 61 μM) at pH 6.0. It is therefore concluded that P. linearisuses primarily CO₂ with HCO₃ ^- being an alternative source of Ci for photosynthesis. Its fast growth could be related to the enzyme carbonic anhydrase whose activity was detected intra- and extracellularly. This revised version was published online in August 2006 with corrections to the Cover Date.     

An improved method for the simultaneous determination of photosynthetic O2 evolution and CO2 consumption in Rhizophora mucronata leaves

The photosynthetic gas-exchange has been assessed traditionally either as O₂ evolution or CO₂ consumption. In this study, we used a liquid-phase O₂ electrode combined with CO₂ optodes to examine simultaneously photosynthesis in intact leaves of mangrove Rhizophora mucronata. We verified suitable conditions for leaf photosynthetic rates by assessing pH levels and NaHCO₃ concentrations and compared these to the gas-exchange method at various PAR levels. The photosynthetic rate in response to pH exhibited a similar pattern both for O₂ evolution and CO₂ consumption, and higher rates were associated with intermediate pH compared with low and high pH values. The net photosynthetic quotient (PQ) of R. mucronata leaves ranged from 1.04–1.28. The PQ values, which were never lesser than 1, suggested that photorespiration did not occur in R. mucronata leaves under aqueous conditions. The similar maximum photosynthetic rates suggested that all measurements had a high capacity to adjust the photosynthetic apparatus under a light saturation condition. The simultaneous measurements of O₂ evolution and CO₂ consumption using the Clark oxygen electrode polarographic sensor with the CO₂ optode sensor provided a simple, stable, and precise measurement of PQ under aqueous and saturated light conditions.     

Anaerobic Formation of d-Lactate and Partial Purification and Characterization of a Pyruvate Reductase from Chlamydomonas reinhardtii

d-Lactate accumulation in Chlamydomonas reinhardtii was dependent on anaerobic conditions. As much as 50% of the ¹⁴C after 2 minutes of photosynthetic ¹⁴CO₂ fixation moved into d-lactate from sugar phosphates if the cells became anaerobic for short time periods. No lactate accumulated in the dark until the O₂ concentration decreased to less than 0.1%. Lactate was determined to be of the d-configuration using stereospecific lactate dehydrogenases. d-Lactate produced anaerobically by algae grown on 5% CO₂ was only slowly metabolized aerobically in the light or dark, and in the dark, only a trace of the lactate was excreted.     

Gas exchange and blood gases of Puna teal (Anas versicolor puna) embryos in the Peruvian Andes

Oxygen consumption, air cell gases, hematology, blood gases and pH of Puna teal (Anas versicolor puna) embryos were measured at the altitude at which the eggs were laid (4150 m) in the Peruvian Andes. In contrast to the metabolic depression described by other studies on avian embryos incubated above 3700 m, O₂ consumption of Puna teal embryos was higher than even that of some lowland avian embryos at equivalent body masses. Air cell O₂ tensions dropped from about 80 toor in eggs with small embryos to about 45 toor in eggs containing a 14-g embryo; simultaneously air cell CO₂ tension rose from virtually negligible amounts to around 26 torr. Arterial and venous O₂ tensions (32–38 and 10–12 toor, respectively, in 12- to 14-g embryos) were lower than described previously in similarly-sized lowland wild avian embryos or chicken embryos incubated in shells with restricted gas exchange. The difference between air cell and arterial O₂ tensions dropped significantly during incubation to a minimum of 11 torr, the lowest value recorded in any avian egg. Blood pH (mean 7.49) did not vary significantly during incubation. Hemoglobin concentration and hematocrits rose steadily throughout incubation to 11.5 g · 100 ml^-1 and 39.9%, respectively, in 14-g embryos.Abbreviations PO₂ partial pressure gradient of O₂ - BM body mass - D diffusion coefficient - G gas conductance (cm³·s^-1·torr^-1) - conductance to water vapor - IP internal pipping of embryos - P _ACO₂ partial pressure of carbon dioxide in air cell - P _AO₂ partial pressure of oxygen in air cell - P _aCO₂ partial pressure of carbon dioxide in arterial blood - P _aCO₂ partial pressure of oxygen in arteries - P _H barometric pressure (torr) - PCO₂ partial pressure of carbon dioxide - P _IO₂ partial pressure in ambiant air - PO₂ partial pressure of oxygen - P _VCO₂ venous carbon dioxide partial pressure - P _VO₂ mixed venous oxygen partial pressure - SE standard error - VO ₂ oxygen consumption     

Effect of anaerobiosis on photosynthetic reactions and nitrogen metabolism of algae with and without hydrogenase

Summary The effect of anaerobic (N₂+CO₂) pre-incubation in the dark on photosynthetic reactions (O₂ evolution, measured manometrically and with the oxygraph; fluorescence; and photoproduction of H₂, measured with the mass spectrometer) was studied in algae with hydrogenase (strains of Chlorella fusca, C. kessleri, C. vulgaris f. tertia, and Ankistrodesmus braunii) and in algae without hydrogenase (strains of Chlorella vulgaris, C. saccharophila, and C. minutissima).The inhibition by anaerobic incubation of photosynthetic O₂ evolution is much stronger in algae without hydrogenase than it is in algae with hydrogenase. The effect of anaerobiosis is most pronounced at rather low light intensity (about 1000 lux), in acid medium (pH 4), and after prolonged anaerobic incubation in the dark (about 20 h). These results indicate that the presence of hydrogenase might be ecologically advantageous for algae under certain conditions.Chlorophyll fluorescence showed the fastest response to anaerobic incubation, and the most pronounced difference between algae with and without hydrogenase. After only 30 min under N₂+CO₂, fluorescence in algae with hydrogenase starts with a peak and decreases within 10 to 20 sec to a rather low steady-state level which is only slightly higher than that found under aerobic conditions. In algae without hydrogenase, fluorescence is rather low during the first 1 to 2 sec and then rises to a higher steady-state level which is much higher than that of the aerobic controls. This indicates an inhibition due to anaerobiosis of photosystem II in algae without hydrogenase.Algae with hydrogenase can react in different ways during the first minutes of illumination. In some cases there is an immediate photoproduction of H₂, which is followed after a few minutes by photosynthetic O₂ evolution; in other algae there is a simultaneous production of H₂ and O₂ from the very beginning; in a few experiments there was no photoproduction of H₂ at all, and in this case there was no photosynthetic O₂ evolution either. Thus, photoproduction of H₂ seems to be the process which normally enables algae with hydrogenase to oxidise and thereby activate their photosynthetic electron transport system after anaerobic incubation.A mass spectrometric search for nitrogen fixation (using N₂ and acetylene) in eucaryotic green algae gave negative results, even with species containing hydrogenase and under anaerobic conditions.     

Enhanced growth of the red algaPorphyra yezoensis Ueda in high CO2 concentrations

Leafy thalli of the red algaPorphyra yezoensis Ueda, initiated from conchospores released from free-living conchocelis, were cultured using aeration with high CO₂. It was found that the higher the CO₂ concentration, the faster the growth of the thalli. Aeration with elevated CO₂ lowered pH in dark, but raised pH remarkably in light with the thalli, because the photosynthetic conversion of HCO ₃ ^? to OH^? and CO₂ proceeded much faster than the dissociation of hydrated CO₂ releasing H⁺. Photosynthesis of the alga was found to be enhanced in the seawater of elevated dissolved inorganic carbon (DIC, CO₂ + HCO ₃ ^? + CO ₃ ^? ). It is concluded that the increased pH in the light resulted in the increase of DIC in the culture media, thus enhancing photosynthesis and growth. The relevance of the results to removal of atmospheric CO₂ by marine algae is discussed.     

Haemoglobin function and respiratory status of the Port Jackson shark,<Emphasis Type="Italic"> Heterodontus portusjacksoni</Emphasis>, in response to lowered salinity

Haemoglobin function and respiratory status of sub-adult sharks, Heterodontus portusjacksoni was investigated for up to 1 week following transfer from 100% to either 75% or 50% seawater. Metabolic rates were unusually low and arterial–venous differences in blood O₂ small. Haemodilution from osmotic inflow lowered haematocrit and reduced blood O₂ content by up to 50%. There was no change in O₂ consumption rate, blood O₂ partial pressure, cardiac output, or the arterial-venous O₂ content difference, and thus O₂ delivery was maintained. Ventilation was acutely elevated but returned to normal within 24 h. The O₂ delivery to the tissues was facilitated by decreased blood O₂-affinity that could not be simply ascribed to changes in the osmolyte concentration. The Hb was unaffected by changes in intra-erythrocyte fluid urea or trimethylamine-N-oxide (TMAO) but was sensitive to changes in NaCl. The Bohr shifts in whole blood were low and there was little role for pH in modulating O₂ transport. Venous Hb saturation remained close to 65%, at the steepest part of the in vivo O₂ equilibrium curve, such that O₂ unloading could be facilitated by small reductions in pressure without increasing cardiac or ventilatory work. H. portusjacksoni tolerated 50% seawater for at least 1 month, but there was little evidence of respiratory responses being adaptive which instead appeared to be consequential on changes in osmotic and ionic status.Abbreviations a–v arterial–venous - CO ₂ CO₂ content - C _a O ₂ content of O₂ in arterial blood - C _v O ₂ content of O₂ in venous blood - %E branchial O₂ extraction efficiency - f _v ventilatory frequency - GTP guanosine triphosphate - Hct haematocrit - [Hb] haemoglobin concentration - ITP inosine triphosphate - met[Hb] methaemoglobin - oxygen consumption - NTP nucleoside triphosphate - OEC oxygen equilibrium curve - P _a O ₂ partial pressure of O₂ in arterial blood - P _e O ₂ partial pressure of expired O₂ - P _i O ₂ partial pressure of inspired O₂ - P _in O ₂ inflow partial pressure of O₂ - PO ₂ partial pressure of O₂ - P _out O ₂ outflow partial pressure of O₂ - pH _a arterial blood pH - pH _pl whole blood pH - PV plasma volume - P _v CO ₂ partial pressure of CO₂in venous blood - P _v O ₂ partial pressure of O₂in venous blood - cardiac output - SW seawater - TMAO trimethylamine-N-oxide - ventilation volume Communicated by G. Heldmaier     

Temperature and starvation affect the hemolymph acid-base balance of the xeric yellow scorpion,Leiurus quinquestriatus

Summary Water conservation is crucial for terrestrial animals such as scorpions which generally live in xeric habitats. One route of water loss is evaporation from their book lungs. In order to save water, scorpions may have a high resistance to gas exchange with the environment. If this is so then the partial pressure of CO₂ in their hemolymph, PCO₂, must be high. Does this affect their acid-base balance? Hemolymph PCO₂ and pH in normally-fed or starved desert-dwelling yellow scorpions Leiurus quinquestriatus were studied in vivo as functions of temperature. An ambient temperature increase (lasting at least 3 days) resulted in a rise of PCO₂ and a fall of pH, with thermal coefficients of 1.6 Torr · °C^-1 and-0.016 pH unit · °C^-1, respectively. The thermal coefficients for cell-free hemolymph studied in vitro were the same. At 28 °C, 3–6 weeks of starvation led to a 4.8 Torr increase in PCO₂ and a 0.056 unit decrease in pH. The in vivo PCO₂ values are among the highest, and pH values are the lowest of the terrestrial arthropods studied so far, e.g., at 28 °C they are 29 Torr and 7.15 pH respectively. It is argued that this particular acid-base balance with a marked hypercapnia is typical of a successful xeric air-breathing animal.Abbreviations ABB acid-base balance - PCO₂ partial pressure of CO₂ - PO₂ partial pressure of O₂     

PO2 and pH changes in the retina of the crab Ocypode ryderi: evidence for aerobic glycolysis

Summary The isolated retina of the terrestrial crab Ocypode ryderi exhibits a pronounced lactate production in spite of being supplied with sufficient O₂ (140 torr). To determine whether this lactate production is caused by hypoxic areas in the tissue or represents aerobic glycolysis, oxygen partial pressure and pH measurements with two-channel glass microelectrodes and additional biochemical analyses were carried out on this organ. Distinct profiles were obtained for O₂ partial pressure and pH inside the tissue. At a depth of 200 m different O₂ partial pressure levels could be observed depending on the O₂ partial pressure in the medium (85 torr at 280 torr and 36 torr at 130 torr, respectively). The extracellular pH displays a similar pattern; it reaches a stable value of 7.15 at 100 m inside the tissue. Lowering bath O₂ partial pressure from 280 torr to about 15 torr (hypoxia) induces a decrease of the O₂ partial pressure in the tissue with different time-courses for different tissue depths. However, hypoxia did not change the extracellular pH. Addition of antimycin A (100 mol · 1^-1) to the medium abolishes the O₂ partial pressure gradient and the delayed recovery of the tissue O₂ partial pressure after hypoxia. These results and the biochemical data suggest that in the crab retina a high glycolytic activity occurs simultaneously with oxydative carbohydrate degradation (aerobic glycolysis).Abbreviations AEC Atkinson energy charge - DC bioelectric potential - dw dry weight - HEPES N-[2-Hydroxyethyl]piperazine-N-[2-ethanesulphonic acid] - PCO₂ carbon dioxide partial pressure - PO₂ oxygen partial pressure - P _tO₂ oxygen partial pressure inside the tissue - P _mO₂ oxygen partial pressure in the medium - pH_t pH inside the tissue - pH_m pH in the superfusion medium     

Oxygen stress and reduced growth of Lobelia dortmanna in sandy lake sediments subject to organic enrichment

1. Lobelia dortmanna is a common representative of the small isoetid plants dominating the vegetation in nutrient‐poor lakes in Europe and North America. Because of large permeable root surfaces and continuous air lacunae Lobelia exchanges the majority of O₂ and CO₂ during photosynthesis across the roots. This leads to profound diel pulses of O₂ and CO₂ in sandy sediments with low microbial O₂ consumption rates. The ready radial root loss of O₂ may, however, make Lobelia very susceptible to more reducing sediments. Therefore, we grew Lobelia for 6 months on natural and organically enriched sandy sediments to test how: (i) root oxygenation influenced degradation of organic matter and depth profiles of N and C; (ii) Lobelia and microbial O₂ consumption rates influenced pool size and depth penetration of O₂ in the sediments; and (iii) sediment enrichment influenced growth and mineral nutrition of Lobelia. 2. Naturally low‐organic sediments (0.32% DW) accumulated organic C and N during the experiment as a result of growth of Lobelia and surface micro‐algae. In contrast, surface layers of enriched sediments (0.58, 0.87 and 2.46% DW) lost organic C and N because of enhanced mineralisation rates because of oxygen availability. In deeper layers of enriched sediments no significant differences in organic C and N pools were found between plant‐covered and plant‐free sediments probably because faster organic degradation because of root oxygenation was balanced by release of organic matter from the plants and because short roots with dense Fe‐Mn coatings in the most enriched sediments constrained O₂ release. 3. Depth‐integrated O₂ pools were much higher in light than darkness, higher in plant‐covered than plant‐free sediments and higher in sandy than in organically enriched sediments. All sediments had a primary O₂ maximum 1–2 mm below the sediment surface in light because of photosynthesis of micro‐algae. Plant‐covered sediments of low organic content (0.32 and 0.58% DW) also had a secondary deep maximum (2–4 cm) because of higher O₂ release from Lobelia roots than microbial O₂ consumption. Nitrification occurred here resulting in depletion of NH and accumulation of NO. In low organic sediments, oxygen pools increased with higher plant biomass both in light and darkness. The deep O₂ and NO₃ maxima disappeared in high organic sediments of greater O₂ consumption rates and smaller O₂ release rates. 4. Lobelia was stressed by increasing O₂ consumption rate of the sediments. Plant weight and leaf number declined twofold and maximum root length declined fourfold suggesting severe problems maintaining sufficient axial O₂ transport to the root tips because of rapid radial O₂ loss. Despite markedly higher nutrient concentrations in the enriched sediments, leaf‐N declined twofold and leaf‐P declined fourfold to growth‐limiting levels. These responses can be explained by constrains on mycorrhisal activity, root metabolism and vascular transport because of O₂ depletion. Management efforts to stop the decline and ensure the recovery of the isoetid vegetation should therefore focus on improving water quality as well as sediment suitability for growth.     

Inhibition of photosynthesis of sunflower leaves by an endogenous solute and interdependence of different photosynthetic reactions

The relationship between components of non-photochemical quenching of chlorophyll fluorescence yield (q_NP) and dissipation of excessive excitation energy was determined in cotton leaves using concurrent measurements of fluorescence and gas-exchange at 2% and 20% O₂ under a range of photon flux densities and CO₂ pressures. A nearly stoichiometric relationship was obtained between dissipation of energy not used in photosynthetic CO₂ fixation or photorespiration and q_NP provided that a component, probably associated with state transitions, was not included in q_NP. Although two distinct components of q_NP were resolved on the basis of their relaxation kinetics, both components appear effective in energy dissipation. The photon yield of open photosystem-II reaction centers decreased linearly with increases in q_NP, indicating that much of the energy dissipation occurs in the pigment bed. However, increases in q_NP appear dependent on the redox state of these centers. The results are discussed in relation to current hypotheses of the molecular basis of non-radiative energy dissipation. It is concluded that determinations of q_NP can provide a quantitative measure of the dissipation of excessive excitation energy if precautions are taken to ensure that the maximum fluorescence yield is measured under conditions that provide complete closure of the photosystem-II reaction centers. It is also concluded that such dissipation can prevent photoinhibitory damage in cotton leaves even under extreme conditions where as much as 80% of the excitation energy is excessive.Abbreviations and symbols F _M, F _O, F _V, F _S fluorescence yield when all PSII centers are closed, when all centers are open, F_M-F_O, at steady state in the light - PFD photon flux density (photon fluence rate) - P(CO₂) sum of rates of CO₂ uptake and dark respiration - P(ET) sum of P(CO₂) and rate of oxygenation - PSI, PSII photosystem I, II - q_NP, q_P non-photochemical, photochemical fluorescence quenching - Q the acceptor for PSII - Q _r/Q _t the fraction of reduced Q or closed PSII centers - _r/ _t intrinsic photon yield of CO₂ fixation in the absence of photorespiration of O₂ evolution - _a P(ET)/PFD (absorbed light) C.I.W. Publication No. 1016     

SO2 and NO2 effects on microbial activity in an acid forest soil

The rate of glucose decomposition and the pH fell in a forest soil (initial pH 4.06) exposed to 1.0 ppm SO₂. No such effect was noted if the soil was exposed to 1.0 ppm nitrogen dioxide (NO₂). Nitrite but not bisulfite (5g N or S/g of soil) inhibited O₂ consumption and CO₂ evolution in the glucose-amended forest soil, and nitrite and bisulfite acted synergistically in inhibiting these processes. Iron and manganese were solubilized when the soil was exposed to 10 ppm SO₂, but NO₂ caused no such change.     

Inorganic-carbon transport in some marine eukaryotic microalgae

Inorganic-carbon transport was investigated in the eukaryotic marine microalgaeStichococcus minor, Nannochloropsis oculata and aMonallantus sp. Photosynthetic O₂ evolution at constant inorganic-carbon concentration but varying pH showed thatS. minor had a greater capacity for CO₂ rather than HCO ₃ ^– utilization but forN. oculata andMonallantus HCO ₃ ^– was the preferred source of inorganic carbon. All three microalgae had a low affinity for CO₂ as shown by the measurement of inorganic-carbon-dependent photosynthetic O₂ evolution at pH 5.0. At pH 8.3, where HCO ₃ ^– is the predominant form of inorganic carbon, the concentration of inorganic carbon required for half-maximal rate of photosynthetic O₂ evolution [K _0.5 (CO₂)] was 53 M forMonallantus sp. and 125 M forN. oculata, values compatible with HCO ₃ ^– transport. Neither extra- nor intracellular carbonic anhydrase was detected in these three microalgal species. It is concluded that these microalgae lack a specific transport system for CO₂ but that HCO ₃ ^– transport occurs inN. oculata andMonallantus, and in the absence of intracellular carbonic anhydrase the conversion of HCO ₃ ^– to CO₂ may be facilitated by the internal pH of the cell.     

Evidence for the contribution of pseudocyclic photophosphorylation to the energy requirement of the mechanism for concentrating inorganic carbon in Chlamydomonas

Mass-spectrometric measurements of ¹⁶O₂ and ¹⁸O₂ were made to compare the rates of light-dependent O₂ evolution and uptake by Chlamydomonas reinhardtii Dang. grown in air (0.035% CO₂; low-C_i cells) or CO₂-enriched air (5% CO₂; high-C_i cells) at pH 5.5 and 8.0. While at pH 5.5, no differences were observed in the isotopic O₂-gas exchange of high- and low-C_i cells, at pH 8.0 the rates of true O₂ evolution and uptake were considerably higher in low-C_i than in high-C_i cells. The enhanced rates of O₂ uptake and evolution by low-C_i cells were completely inducible within 6 h after transferring high-C_i cells to ambient air. At pH 8.0, O₂ uptake in the light was inhibited by 2 M 3-(3,4-dichlorophenyl)-1,1 dimethylurea in both types of alga, but this effect was more pronounced in low-C_i than in high-C_i cells.When the cells were grown at pH 5.5 the activities of the superoxide-radical-degrading enzymes, superoxide dismutase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase, were similar regardless of the CO₂ concentration provided during growth. At pH 8.0, however, the activities of these enzymes were 4 to 20 times higher in low-C_i than in high-C_i cells. When high-C_i cells were allowed to acclimate to ambient air for 6 h at pH 8.0, the activities of superoxide dismutase, ascorbate peroxidase and monodehydroascorbate dehydrogenase increased to more than 50% of the level observed with low-C_i cells. These results are consistent with an enhanced operation of O₂ photoreduction which could provide energy to the inorganic-carbon-concentrating mechanism via pseudo-cyclic photophosphorylation.