Measurement of the Carbon Dioxide Compensation Point and the Rate of Loss of 14CO2 in the Light and Dark in Some Bryophytes

The CO₂ compensation point at 25 °C and 250 µEinsteinsm^–2 s^–1 wasmeasured for 27 bryo-phyte species, andwas found to be in the range of 45–160 µl CO₂ I^–1air. Under the same conditions Zea mays gave a value of 11 µlI^–1 and Horde um vulgare 76 µI^–1. The rate of loss of photosyntheticallyfixed ¹⁴CO₂ in the light and dark in six bryophytes (three mosses,two leafy liverworts, one thalloid liverwort) was determinedin CO₂-free air and 100% O₂. The rate of ¹⁴CO₂ evolution inthe light was less than that in the dark in CL₂-free air, butin 100% O₂ the rate in the light increased, so that in all butthe leafy liverworts it was greater than that in the dark. Raisingthe temperature tended to increase the rate of 14CO₂ evolutioninto CO₂-free air both in the light and dark, so that the light/dark(L/D) ratio did not greatly vary. The lower rate of loss of¹⁴CO₂ in the light compared tothe dark could be due to partialinhibition of ‘dark respiration’ reactions in thelight, a low rate of glycolate synthesis and oxidation, or partialreassimilation of the ¹⁴CO₂ produced, or a combination of someor all of these factors.     

Effect of Temperature on Photosynthesis and Photorespiration of Wheat Leaves

Wheat plants were grown in a controlled environment with daytemperatures of 18 ?C and with 500 µ Einsteins m^–28^–1 of photosynthetically active radiation for 16 h. Beforeanthesis and 2 to 3 weeks after, rates of net photosynthesiswere measured for leaves in 2 or 21% O₂ containing 350 vpm CO₂at 13, 18, 23, and 28 ?C and with 500 µEinsteins m^–2s^–1 of photosynthetically active radiation. Also, underthe same conditions of light intensity and temperature, therates of efflux of CO₂ into CO₂-free air were measured and,for mature flag leaves 3 to 4 weeks after anthesis, gross andnet photosynthesis from air containing 320 vpm ¹⁴CO₂ of specificactivity 39?7 nCi µmol^–1. When the O₂ concentration was decreased from 21 to 2% (v/v)the rate of net photosynthesis increased by 32 per cent at thelowest temperature and 54 per cent at the highest temperature.Efflux of CO₂ into CO₂-free air ranged from 38 per cent of netphotosynthesis at 13 ?C to 86 per cent at 28 ?C. Gross photosynthesis,measured by the ¹⁴C assimilated during 40 s, was greater thannet photosynthesis by some 10 per cent at 13 ?C and 17 per centat 28 ?C. These data indicate that photorespiration was relativelygreater at higher temperatures.     

Modification of the CO2 Responses of Maize Stomata by Abscisic Acid and by Naturally-Occurring and Synthetic Cytokinins

Fragments of maize leaves were incubated at controlled temperatureand irradiance either on distilled water or on one of threeconcentrations of cytokinin (10^–1, 10^–2 and 10^–3mol m^–3). The effects of zeatin or kinetin on stomatalaperture were determined by stripping abaxial epidermis fromthe fragments after incubation and immediately measuring stomatalapertures under the microscope. At each cytokinin concentrationleaf pieces were incubated at 5 or 350 µmol mol^–1CO₂ with or without ABA (10^–1 mol m^–3). At 5.0 µmolmol^–1 CO₂ increasing the concentrations of zeatin hada negligible effect upon stomatal aperture. When air containing350 umol mol^–1 CO₂ was bubbled through the incubationsolutions, apertures of stomata incubated on water were morethan halved. Increasing cytokinin concentrations reduced theeffect of CO₂ on stomata and incubation on 10^–1 mol m^–3zeatin completely removed any CO₂ response. The addition ofABA restored the effect of CO₂, even at the highest cytokininconcentration. Key words: Maize, CO₂ response, ABA, Cytokinins     

Photosynthetic carbon metabolism in photoautotrophically and photomixotrophically cultured tobacco cells

Labeling patterns of light and dark ¹⁴CO₂-fixation in photoautotrophicallyand photomixotrophically cultured tobacco cells were determined.During short term ¹⁴CO₂ fixation under light, malate(C₃–C₃carboxylation) was heavily labeled as were phosphoglyceric acidand sugar phosphates(C₁–C₅ carboxylation). Dark fixationcould not account for this high ¹⁴CO₂ incorporation into theC₄ compounds linked to PEPCase. Two carboxylation pathways linkedto the RuBPCase and PEPCase were indicated in ¹⁴CO₂-fixationin light in photoautotrophically and photomixotrophically culturedcells. (Received October 25, 1979; )     

Bisulfite compounds as metabolic inhibitors: nonspecific effects on membranes

Bisulfite compounds are shown to be nonspecific inhibitors ofphotosynthetic processes and of ion transport in green tissues.CO₂ fixation and light-dependent transient changes in externalpH are inhibited about 50% by 5x10^–4 M glyoxal-Na-bisulfite.Chloride uptake in the light and in the dark is inhibited tothe same extent at this concentration. At 5x10^–3 M theinhibitor reduces ATP levels in the light and in the dark, andeffects on glycolate oxidase and PEP carboxylase are observed.The extent of inhibition is dependent on time of treatment withglyoxal-Na-bisulfite and freshly prepared NaHSO₃ is equallyas effective as the addition compound. Possible explanations of the bisulfite effects and the relationshipsto SO₂ effects on photosynthesis are discussed. (Received September 1, 1971; )     

Sources of Inorganic Carbon Acquired through CAM in Littorella uniflora (L.) Aschers

Madsen, T. V. 1987. Sources of inorganic carbon acquired throughCAM in Littorella uniflora (L.) Aschers.—J. exp. Bot.38: 367–377. The CO₂ dynamics of the lacunal air and the relative contributionof external and internal CO₂ sources to dark CO₂ assimilationwas examined in the submerged aquatic CAM species Littorellauniflora (L.) Aschers. Refixation of internal CO₂, released by dark respiration, constitutedabout 30–35% of the total dark CO₂ assimilation. At aCO₂ concentration of 0·2 mol m^–3 around the leavesthe external CO₂ uptake through the roots increased from 45%of the total CO₂ uptake at 0·7 mol m^–3 CO₂ to 100%at 1·6 mol m^–3 and 3·1 mol m^–3 CO₂around the roots. The negligible importance of leaf CO₂ uptakeat high CO₂ concentrations around the roots was the result ofa causative high CO₂ concentration in the leaf lacunae. The CO₂ permeability of Littorella leaves was high relativeto root permeability. This has at least two ecological implications:(1) it enhances the potential diffusive release of CO₂ fromthe sediment C0₂-pool via the lacunal system of the plants.This loss of CO₂, however, was found to be greatly reduced byCAM activity of the plants. (2) The high permeability of theleaf surface to CO₂ exchange allows the plants to assimilateCO₂ from the water surrounding the leaves when the concentrationis high, i.e. during extensive epiphyte dark respiration. Thus,CAM tends to facilitate retension of a high CO₂ pool in thesediment-plant system and at the same time allows the plantsto exploit the water column CO₂ source when it is abundant.This result is in accordance with the general idea that CAMin aquatics constitute a carbon conserving mechanism. Key words: Aquatic macrophytes, dark CO₂ assimilation, inorganic carbon sources     

Photosynthetic Carbon Sources of Stream Macrophytes

Rates of photosynthesis of four submerged stream macrophyteswere examined under varying pH and composition of inorganiccarbon species. Callitriche stagnatis and Sparganium simplexused only CO₂ for photosynthesis. Potamogeton crispus and P.pectinatus used HCO₃ in addition to CO₂, but with much lowerefficiency. The photosynthetic rates at air equilibrium anda total inorganic carbon concentration of 5.0 mM were 2–3times lower than maximum rates at CO2 saturation for the HCO₃users and 10–14 times lower for the CO₂ users. The CO₂compensation point of entire plants of Callitriche (2.5 µM)and Sparganium (6.0µM) was well below the equilibriumconcentration (15 µM). and the low saturation points (250–500µM) also pointed to efficient use of CO2. Callitricheand Sparganium compete successfully with HCO₃^– users inhardwater streams, which have a higher exchange and generationcapacity of CO2 than stagnant and more soft waters. Rates ofphotosynthesis of Potamogeton crispus and P. pectinatus decreasedat high pH. Depending on the two alternative hypotheses forHCO₃use, this decline can be explained by CO₃^––inhibition of HCO₃^– uptake or by increasing capacity tobuffer H+efflux from the plant. Habitats subject to high pH,e. g. small ponds with dense vegetation, may have a strong selectionfor efficient mechanisms of HCO₃ use. Key words: Photosynthesis, Macrophytes, Carbon-source     

EFFECTS OF CHLORAMPHENICOL AND KINETIN ON UPTAKE AND INCORPORATION OF AMINO ACIDS BY TOBACCO LEAF DISKS

The effects of chloramphenicol and kinetin on uptake and incorporationof ³⁵S-methionine and some ₁₄C-amino acids have been investigatedin leaf-disks of Nicotiana rustica in light and dark. Chloramphenicolin a concentration of 1 mg per ml inhibits the uptake of aminoacids from 30 to 60 per cent compared with the water control.The incorporation of amino acids into bulk protein is stronglyinhibited in light (40 to 70 per cent), but only to a smalldegree in dark (10 to 20 per cent), as revealed also by ¹⁴CO₂-photosynthesisof the disks and following treatment with chloramphenicol indark. The stimulating effect of kinetin on uptake and incorporationof amino acids is dependent upon its concentration (10^–5to 10^–6 M ; but 10^–4 M solution inhibits stronglyboth uptake and incorporation). The stimulation seems to influencemore incorporation than uptake processes. Possible interactionsof chloramphenicol and kinetin in the protein metabolism oftobacco leaves have been discussed. (Received April 27, 1964; )     

Long Term Effects of High CO2 Concentration on Photosynthesis of Water Hyacinth (Eichhornia crassipes (Mart.) Solms)

The photosynthetic response to CO₂ concentration, light intensityand temperature was investigated in water hyacinth plants (Eichhorniacrassipes (Mart.) Solms) grown in summer at ambient CO₂ or at10000 µmol(CO₂) mol^–1 and in winter at 6000 µmol(CO₂)mol^–1 Plants grown and measured at ambient CO₂ had highphotosynthetic rate (35 µmo1(CO₂) m^–2 s^–1),high saturating photon flux density (1500–2000) µmolm^–2 s^–1 and low sensitivity to temperature in therange 20–40 °C. Maximum photosynthetic rate (63 µmol(CO₂)m^–2 s^–1) was reached at an internal CO₂ concentrationof 800 µmol mol^–1. Plants grown at high CO₂ in summerhad photosynthetic capacities at ambient CO₂ which were 15%less than for plants grown at ambient CO₂, but maximum photosyntheticrates were similar. Photosynthesis by plants grown at high CO₂and high light intensity had typical response curves to internalCO₂ concentration with saturation at high CO₂, but for plantsgrown under high CO₂ and low light and plants grown under lowCO₂ and high light intensity photosynthetic rates decreasedsharply at internal CO₂ concentrations above 1000 µmol^–1. Key words: Photosynthesis, CO₂, enrichment, Eichhornia crassipes     

Photosynthetic Nitrogen Metabolism in High and Low CO2-adapted Scenedesmus: I. INORGANIC CARBON-DEPENDENT O2 EVOLUTION, NITRATE UTILIZATION AND NITROGEN RECYCLING

Larsson, M., Larsson, C.-M. and Guerrero, M. G. 1985. Photosyntheticnitrogen metabolism in high and low CO₂-adapted Scenedesmus.I. Inorganic carbon-dependent O2 evolution, nitrate utilizationand nitrogen recycling.—J. exp Bot. 36: 1373–1386 Scenedesmus obtusiusculus Chod. was grown on an inorganic mediumflushed with either air or air supplemented with 3% CO₂. Inair-grown cells, O₂ evolution dependent on low, but not high,HCO^–₃ concentrations was strongly inhibited by the carbonicanhydrase inhibitor acetazolamide. Cells grown with 3% CO² exhibitedlow rates of O2 evolution at low external inorganic C; however,after 30 min in air O2 evolution rates at low inorganic C approachedthose of air-grown cells. These results are compatible withthe view that Scenedesmus develops a ‘CO² concentratingmechanism’ in air, with carbonic anhydrase as an importantconstituent When 3% CO²-grown cells were subjected to air-level of CO²,just a transient decline in NO^–₃ utilization was observed,but in the presence of acetazolamide the rate of the processdecreased drastically in response to the decrease in the CO²level. In CO²-free air NO₃^– was taken up at high ratesbut in a deregulated manner, leading to release of NH₄⁺. A portionof the NO₃^– taken up in the absence of CO² was apparentlyassimilated Cellular nitrate reductase (NR) activity initially decreasedbut subsequently recovered after a transition from 3% CO² toair. In the presence of acetazolamide, a persistent decreasein NR activity was observed. Cellular glutamine synthetase (GS)activity increased after transition from 3% CO² to air, theactivity increase being unaffected by acetazolamide. NH₄⁺ releaseto the medium in the presence of L-methionine-D, L-sulphoximine(MSO) transiently increased in 3% CO²-grown cells in responseto a transfer to air. MSO-induced NH₄⁺ release was in fact higherin air-grown cells than in 3% CO²-grown cells. Glycollate wasinitially released after transition from 3% CO² to air, butthere was no difference in glycollate release between MSO-treatedand untreated cells. In air-adapted Scenedesmus, N recyclingseems to be of minor importance in comparison to primary N assimilation Key words: CO²-fixation, N recycling, nitrate uptake, Scenedesmus     

Studies on the Role of Photosynthesis in the Photoperiodic Induction of Flowering in the Short-Day Plants Kalanchoe blossfeldiana Poellniz and Xanthium pensylvanicum Wallr: I. THE REQUIREMENT FOR CO2 DURING PHOTOPERIODIC INDUCTION

It has been established that Kalanchoe blossfeldiana and Xanthiumpensylvanicum require CO₂ during the light period of short daysfor successful photoperiodic induction of flowering, even ifall but the induced leaf are held in normal air. In X. pensylvanicumfloral induction in normal air was independent of the starchstatus of the leaves but when reserves were reduced, lack ofCO₂ in the light suppressed floral induction to an even greaterextent. Injection into the induced leaf (Kalanchoe) or leaftip feeding (Xanthium) of carbohydrates, organic and amino acidsor several other metabolites failed to substitute for the CO₂requirement for induction. A small response was produced by10 mg ml^–1 sucrose in X. pensylvanicum while in normalair 25 parts 10^–6 ATP reduced the time to flowering inK. blossfeldiana and 10^–4 M proline was inhibitory. Anexperiment on the light requirement established a need for redlight ( max 660 nm) during photoperiods but red light alonedid not facilitate maximal induction. It is concluded that someearly, possibly labile, product of photosynthetic CO₂ fixationis essential to floral induction in these species.     

Physiological Studies of the Sulpholipids of Diatoms

The sulpholipids of three species of freshwater and marine diatomNitzschia palae Kutz, Navicula muralis Lewin and Navicula incertaGrün, have been investigated under various culture conditions.The plant sulpholipid, sulphoquinovosyl diglyceride, was predominantlysynthesized in the light rather than in the dark while the unknownsulpholipids, designated as U₁ and U₂, were produced more inthe dark than in the light. It was found that cells starvedof carbon or sulphate utilized their sulpholipid reserve assources of these materials. Generally, cultures incubated inthe light and bubbled with air (with or without CO₂) showeda high level of incorporation of ³⁶S into sulpholipids. In culturesbubbled with oxygen-free nitrogen the incorporation of tracerwas very small. The photosynthetic and respiratory inhibitors,DCMU and DNP appreciably reduced the amount of tracer incorporatedinto the sulpholipids.     

Regulation of CO2-fixation in Chlorella by light of varied wavelengths and intensities

1) The wavelength effects on ¹⁴CO₂-fixation by Chlorella cellswere studied, using monochromatic light of different light intensities. 2) Blue light (453 mµ) stimulated the incorporation of¹⁴C into aspartate, glutamate and malate. Red light (679 mµ),on the other hand, stimulated its incorporation into P-esters,free sugars and insoluble material. 3) The blue light effect was observed in the presence of CMUat concentrations completely suppressing ordinary photosyntheticCO₂-fixation. 4) The blue light effect in the presence of CMU was inducedat very low intensities. At 453 mµ, 300 erg cm^–2sec^–1 was sufficient for complete saturation. 5) Time courses of ¹⁴C-incorporation into individual compoundswere investigated. Irrespective of the wavelength of the illuminatinglight, the first stable CO₂-fixation product formed under weaklight (400–500 erg cm^–2 sec^–1) was citrulline.At higher light intensities (4,000–7,000 erg cm^–2sec^–1), PGA was the first stable CO₂-fixation product.The incorporation of ¹⁴C into citrulline was not inhibited byCMU. 6) Experimental results indicate that both blue light-inducedincorporation of ¹⁴C into amino and organic acids and the incorporationof ¹⁴C into citrulline induced by low intensity light are operatedby a mechanism(s) independent of ordinary photosynthetic CO₂-fixation.Possible effects of light regulating the carbon metabolism inalgal cells are discussed. (Received July 24, 1969; )     

Effects of elevated CO2 concentrations on three montane grass species: III. Source leaf metabolism and whole plant carbon partitioning

Agrostis capillaris L.⁵, Festuca vivipara L. and Poaalpina L.were grown in outdoor open-top chambers at either ambient (340 3µmol mol^–1) or elevated (6804µmol mol^–1)concentrations of atmospheric carbon dioxide (CO₂) for periodsfrom 79–189 d. Photosynthetic capacity of source leaves of plants grown atboth ambient and elevated CO₂ concentrations was measured atsaturating light and 5% CO₂. Dark respiration of leaves wasmeasured using a liquid phase oxygen electrode with the buffersolution in equilibrium with air (21% O₂, 0.034% CO₂). Photo-syntheticcapacity of P. alpina was reduced by growth at 680 µmolmol^–1 CO₂ by 105 d, and that of F. vivipara was reducedat 65 d and 189 d after CO₂ enrichment began, suggesting down-regulationor acclimation. Dark respiration of successive leaf blades ofall three species was unaltered by growth at 680 relative to340 µmol mol^–1 CO₂. In F. vivipara, leaf respirationrate was markedly lower at 189 d than at either 0 d or 65 d,irrespective of growth CO₂ concentration. There was a significantlylower total non-structural carbohydrate (TNC) concentrationin the leaf blades and leaf sheaths of A. capillaris grown at680µmol mol^–1 CO₂. TNC of roots of A. capillariswas unaltered by CO₂ treatment. TNC concentration was increasedin both leaves and sheaths of P. alpina and F. vivipara after105 d and 65 d growth, respectively. A 4-fold increase in thewater-soluble fraction (fructan) in P. alpina and in all carbohydratefractions in F. vivipara accounted for the increased TNC content. In F. vivipara the relationship between leaf photosyn-theticcapacity and leaf carbohydrate concentration was such that therewas a strong positive correlation between photosynthetic capacityand total leaf N concentration (expressed on a per unit structuraldry weight basis), and total nitrogen concentration of successivemature leaves reduced with time. Multiple regression of leafphotosynthetic capacity upon leaf nitrogen and carbohydrateconcentrations further confirmed that leaf photosynthetic capacitywas mainly determined by leaf N concentration. In P. alpina,leaf photosynthetic capacity was mainly determined by leaf CHOconcentration. Thus there is evidence for down-regulation ofphotosynthetic capacity in P. alpina resulting from increasedcarbohydrate accumulation in source leaves. Leaf dark respiration and total N concentration were positivelycorrelated in P. alpina and F. vivipara. Leaf dark respirationand soluble carbohydrate concentration of source leaves werepositively correlated in A. capillaris. Changes in source leafphotosynthetic capacity and carbohydrate concentration of plantsgrown at ambient or elevated CO₂ are discussed in relation toplant growth, nutrient relations and availability of sinks forcarbon. Key words: Elevated CO₂, Climate change, grasses, carbohydrate partitioning, photosynthesis, respiration     

The Damping and Reinitiation of the Circadian Rhythm of CO2 Output in Bryophyllum Leaves in Relation to their Malate Content

The circadian rhythm of CO₂ output in leaves of Bryophyllumfedtschenkoi damps out after 3–4 d in continuous darknessand a CO₂-free air stream at 15°C. The rhythm is reinitiatedafter a single exposure to white light of 2, 4, 6 or 8 h duration,damps out again after a further 3–4 d and can be reinitiatedfor a second time by a further exposure to light. During the exposure to light there is a burst of CO₂ outputconsistent with the decarboxylation of malate, and the rhythmbegins afterwards with an initial high rate of CO₂ fixation.Malate gradually accumulates in the leaves in continuous darknessto attain a maximum value (35 mol m^–3) at the time whenthe circadian rhythm disappears, and decreases to a low value(19 mol m^–3) after a 4 h exposure to light which reinitiatesrhythmicity. These results support the hypothesis that damping of the rhythmof CO₂ output in continuous darkness is due to the accumulationof malate in the leaf cells, eventually reaching such a levelthat its removal from the cytoplasm into the vacuole cannottake place, with the result that PEPc activity, upon which therhythm of CO₂ output depends, remains allosterically inhibited. Key words: CAM, circadian rhythm, Bryophyllum, CO₂-fixation, malate metabolism     

Diurnal regulation of NO-3 uptake in soybean plants IV. Dependence on current photosynthesis and sugar availability to the roots

The short-term dependence of NO^–₃ uptake upon photosynthesisand sugar supply to the roots of soybean plants was investigatedin a series of experiments where CO₂ availability, light intensityor conduction of phloem sap to the roots were severely limited.Removal of CO₂ from the atmosphere or girdling of the stem equallyprevented the stimulation of NO^–₃ uptake when plants weretransferred from darkness to the light. The effect of thesetwo treatments can be reversed by CO₂ re-supply or by additionof 10 mM glucose in the nutrient solution, respectively. Glucosewas also more effective in stimulating NO^–₃ uptake byintact plants in darkness than in light. Collectively, theseobservations are interpreted as evidence that the diurnal changesin NO^–₃ uptake are due to decreased phloem transport ofphotosynthates in darkness. Accordingly, the magnitude of thesechanges was much dependent on starch accumulation in the leavesat the end of the photo-period. Shading the plants lowered thisaccumulation, and resulted in an amplification of the diurnalchanges in NO^–₃ uptake. These results are discussed inconnection with the hypothesis that the carbon-dependent plasticityof the night/day ratio of NO^–₃ uptake is an importantfeature of the co-ordination of the acquisition of N and C bythe plant. Key words: Glycine max, light/dark cycle, NO^–₃ uptake, C and N acquisition     

Oxygen as an Enviromnental Factor in Influencing Normal Morphogenetic Development in Germinating Rice Seedlings

Rice seedlings germinated in the dark in O₂-deficient and normalair environments manifest dimorphism and are designated hereas d^– and d⁺ plants. Both d^– and d⁺ seedlings lackchlorophyll but the d^– plants are stark-white whereasthe d⁺ plants are yellow or yellow-green in appearance. Riceseedlings germinated in the light under O₂ deficiency also lackchlorophyll and manifest the same developmental characteristicsas the d^– dark-germinated seedlings. Thus, in an O₂-deficientenvironment, light-germinated rice seedlings behave as thoughthey were germinated in the dark under O₂ deficiency. Exposureof the dark-germinated d^– and d⁺ seedlings and the light-germinatedd^– seedlings to normal air in the light brings about chlorophyllformation and normal morphogenetic development in all threetypes of germinating seedlings. Thus O₂ exerts a critical influenceon the response of germinating rice seedlings to light energywith respect to their normal morphogenetic development.     

Photosynthetic Net CO2 Uptake and Leaf Phosphate Concentrations in CO2 Enriched Clover (Trifolium subterraneum L.) at Three Levels of Phosphate Nutrition

Net CO₂-uptake of sets of clover plants (Trifolium subterraneumL.) was measured over 3 weeks in ambient air and in a highlyCO₂-enriched atmosphere (400 Pa CO₂). Phosphate (P) in the nutrientsolution was varied between 0·05 mol m^–3 P (reducedP) and 2·0 mol m^–3 P (high P). In ambient air,the daily increments of the daily rate of net CO₂-uptake (DICU;a parameter related to relative growth) were higher at reducedP than at high P. Stimulation by high CO₂ of net CO₂-uptakein the first day was less at reduced P than at high P. In thefollowing days, high CO₂ markedly inhibited DICU at reducedP, and thus growthstimulation by high CO₂ ceased after between4 and 12 d. By contrast, at high P, DICU increased more than2-fold upon CO₂-enrichment, and thus growth stimulation by highCO₂ was maintained. Intermediate results were obtained withhalf-strength Hoagland's solution (0·5 mol m^–3P). Leaf pools of inorganic ortho P, soluble esterified P, and totalP declined markedly in high CO₂ when P-nutrition had been reduced.Considerable decline also occurred in high CO₂ when P-nutritionhad been increased suggesting that P-uptake was not well tunedwith net CO₂-uptake (growth). It is proposed that high CO₂ can perturb the P-metabolism ofclover, the impairment being less at high levels of P-nutrition.With regard to high CO₂ as a growth stimulus, these resultsdemonstrate that increasing P-nutrition to a level supraoptimalin ambient air can considerably improve the growth of a C₃-plantin high CO₂. Key words: Atmospheric CO₂-enrichment, phosphate nutrition, photosynthesis, clover     

Carbon Dioxide Exchange of Developing Apple (Malus pumila Mill.) Fruits

The carbon dioxide exchange of developing apple fruits was monitoredduring development. The results of measurements on detachedfruits in the laboratory were consistent with those made onattached fruit in the field. Respiration rate at 20 °C inthe dark declined from 120 ng CO₂ g^–1 fr. wt. s_–1on 5 June (4 weeks after full bloom) to less than 3 ng g^–1fr. wt. s^–1 by late September. In the light, net CO₂ evolutionwas much decreased, but on no occasion did photosynthesis exceedrespiration and no net CO₂ uptake was detected. The Q₁₀ fordark respiration over the interval from 15 to 25 °C changedfrom 2.8 in early June to 1.6 in early August     

Alkalization of the Medium by Unicellular Green Algae during Uptake Dissolved Inorganic Carbon

When Chlorella vulgaris 11h, Chlorella vulgaris C-l, Chlamydomonasreinhardtii, Chlamydomonas moewusii, Scenedesmus obliquus, orDunaliella tertiolecta were illuminated in with 0.5 mM NaHCO₃,the pH of the medium increased in a few minutes from 6 to about9 or 10. The alkalization, which was accompanied by O₂ evolution,was dependent on light, external dissolved inorganic carbon(DIC) as HCO^-₃, and algae grown or adapted to a low, air-levelCO₂ in order to develop a DIC concentrating mechanism. Therewas little pH increase by algae without a DIC concentratingprocess from growth on 3% CO₂ in air. Photosynthetic O₂ evolutionwithout alkalization occurred using either internal DIC or externalCO₂ at acidic pH. The PH increase stopped between pH 9 to 10,but the alkalization would restart upon re-acidification betweenpH 6 and 8. Alkalization was suppressed by the carbonic anhydraseinhibitors, acetazolamide, ethoxyzolamide or carbon oxysulfide.The pH increase appeared to be the consequence of the externalconversion of HCO^–₃ into CO₂ plus OH^– during photosynthesisby cells with a high affinity for CO₂ uptake. Cells grown onhigh CO₂ to suppress the DIC pump, when given low levels ofHCO^–₃ in the light, acidified the medium from pH 10 to7. Air adapted Scenedesmus cells with a HCO^–₃ pump, aswell as a CO₂ pump, alkalized the medium very rapidly in thelight to a pH of over 10, as well as slower in the dark or inthe light with DCMU or without external DIC and O₂ evolution.Alkalization of the medium during photosynthetic DIC uptakeby algae has been considered to be part of the global carboncycle for converting H₂CO₃ to HCO^–₃ and for the formationof carbonate salts by calcareous algae from the alkaline conversionof bicarbonate to carbonate. These processes seem to be a consequenceof the algal CO₂ concentrating process. ¹Present address: Department of Biology, Faculty of Science,Niigata University, Niigata, 950-21 Japan.