The Influence of Partial Pressure of Carbon Dioxide upon Carbon Metabolism in the Tomato Leaf

The incorporation of radioactive carbon into various photosyntheticproducts was investigated with tomato plants in atmospherescontaining between 40 and 1400 parts/10⁶ carbon dioxide. A significantlygreater proportion of ¹⁴C entered sucrose and alcohol-insolublematerial at high concentrations of carbon dioxide. Incorporationinto glycine and serine was significantly greater at lower carbon-dioxideconcentrations. The pool size of these intermediates was alsodetermined and it was concluded that in the presence of highpartial pressures of carbon dioxide the flow of carbon fromthe photosynthetic cycle through the C² pathway is decreased.     

Short- and Long-Term Inhibition of Respiratory Carbon Dioxide Efflux by Elevated Carbon Dioxide

Dark carbon dioxide efflux rates of recently fully expandedleaves and whole plants of Amaranthus hypochondriacus L., Glycinemax (L.) Merr., and Lycopersicon esculentum Mill. grown in controlledenvironments at 35 and 70 Pa carbon dioxide pressure were measuredat 35 and 70 Pa carbon dioxide pressure. Harvest data and whole-plant24-h carbon dioxide exchange were used to determine relativegrowth rates, net assimilation rates, leaf area ratios, andthe ratio of respiration to photosynthesis under the growthconditions. Biomass at a given time after planting was greaterat the higher carbon dioxide pressure in G. max and L. esculentum,but not the C₄ species, A. hypochondriacus. Relative growthrates for the same range of masses were not different betweencarbon dioxide treatments in the two C₃ species, because highernet assimilation rates at the higher carbon dioxide pressurewere offset by lower leaf area ratios. Whole plant carbon dioxideefflux rates per unit of mass were lower in plants grown andmeasured at the higher carbon dioxide pressure in both G. maxand L. esculentum, and were also smaller in relation to daytimenet carbon dioxide influx. Short-term responses of respirationrate to carbon dioxide pressure were found in all species, withcarbon dioxide efflux rates of leaves and whole plants lowerwhen measured at higher carbon dioxide pressure in almost allcases. Amaranthus hypochondriacus L., Glycine max L. Merr., Lycopersicon esculentum Mill., soybean, tomato, carbon dioxide, respiration, growth     

A Null Balance Carbon Dioxide and Water Vapour Porometer

The Binos IRGA is suitable for portable use in the field aftermodification and can be added to the null-balance water vapourdiffusion porometer in a closed loop with the porometer chamberand used as a null-balance indicator for measurements of CO²flux, without the need for substantial structural or electricalmodification. The null-balance concept works satisfactorily in the measurementof both CO² influx and efflux and enables the CO² flux to bemeasured at either the ambient CO² concentration or at otherknown CO² concentrations. The combined CO² and water vapour porometer enables measurementsof the rate of photosynthesis, and estimates of stomatal andmesophyll conductance to be made extensively in the field withoutthe need for an elaborate mobile laboratory.     

The Diffusion of Carbon Dioxide and Water Vapour through Stomata

An account is given of the diffusion of carbon dioxide and ofwater vapour through the stomata of leaves in the presence ofair. It shows that the argument given in K. J. Parkinson andH. L. Penman's paper (1970): ‘A Possible Source of Errorin the Estimation of Stomatal Resistance’ is substantiallyincorrect. However, the correction factors to the sugar beetdata presented in their paper are valid owing to a fortuitousset of circumstances including the similarity in magnitude oftwo mutual diffusion coefficients. The concept of stomatal resistanceis criticized.     

Influence of pH upon the Warburg Effect in Isolated Intact Spinach Chloroplasts: I. Carbon Dioxide Photoassimilation and Glycolate Synthesis

The influence of pH upon the O₂ inhibition of ¹⁴CO₂ photoassimilation (Warburg effect) was examined in intact spinach (Spinacia oleracea) chloroplasts. With conditions which favored the Warburg effect, i.e. rate-limiting CO₂ and 100% O₂, O₂ inhibition was greater at pH 8.4 to 8.5 than at pH 7.5 to 7.8. At pH 8.5, as compared with 7.8, there was an enhanced ¹⁴C-labeling of glycolate, and a decrease of isotope in some phosphorylated Calvin cycle intermediates, particularly triose-phosphate. The ¹⁴C-labeling of starch was also more inhibited by O₂ at higher pH. The enhanced synthesis of glycolate during ¹⁴CO₂ assimilation at higher pH resulted in a diminution in the level of phosphorylated intermediates of the Calvin cycle, and this was apparently a causal factor of the increased severity of the Warburg effect.     

On Photosynthesis and Organic Carbon, Carbon Dioxide, and Oxygen Flows in the Ocean

The modern concept of photosynthesis as a mechanism for utilizing the energy of solar radiation is used as the basis for assessing the scale of photosynthetic production of initial organic matter in the ocean (primary biological production), its destruction, the carbon and carbon dioxide cycles (flows) involved in this process, and the size of oil- and gas-bearing hydrocarbonaceous formations originating in sedimentary deposits.     

The Control of Water and Carbon Dioxide Flux in Water-stressed Sugar Beet

Changes in leaf and canopy water potential of sugar beet growingin soil of decreasing water content depended on soil water potentialand were independent of water flux from the plant when thiswas varied by changing the water vapour content of the air.The calculated hydraulic conductance of the plant increasedas flux increased and decreased as leaf water potential decreasedand as the plant aged. The conductances to water vapour of individualleaves and of the canopy decreased as leaf water potential decreasedand increased with increasing humidity of the air. The lattereffect was independent of changes in leaf water potential. Theconductances were not affected by the rate of evaporation orleaf temperature. The rate of photosynthesis was directly relatedto leaf conductance except in severely stressed, mature leavesin which leaf water potential had a more direct effect on photosynthesis.Stomatal conductances, transpiration, and photosynthesis weregreater in young leaves than mature leaves on the same plantand at the same leaf water potential. These results are discussedin relation to current agricultural irrigation practices usedfor sugar beet.     

Carbon Dioxide and Water Vapour Exchange of Leaves on Field-Grown Citrus Trees

Carbon dioxide and water vapour exchange rates were measuredon attached leaves of field-grown citrus trees. The exchangerates were measured continuously during several weeks in thespring of two successive years. These data confirmed the ratherlow rates of maximum CO₂ exchange (6–11 µmol m^–2s^–1) by citrus leaves. However, the maximum rate was maintainedthrough the midday period on only about half the days. On theother days, characterized by high temperatures and high atmosphericwater vapour pressure deficits, pronounced midday depressionsin CO₂ exchange rates were observed. Since midday transpirationremained stable at a constant rate even with increasing vapourpressure deficit, these results indicate that stomatal closurewas occurring. In fact, the data suggest tfiat specific, maximumtranspiration rates were associated with differing rootstocks.Thus, the rate of water supply to the leaves may be an importantfactor in determining the maximum transpiration rate, and therebymediating control of stomatal conductance and the resultantmidday depression in CO² exchange rates.     

Apparatus for the Simultaneous Measurement of Water Vapour and Carbon Dioxide Exchanges of Single Leaves

Equipment is described which delivers air with concentrationsof CO₂ and water vapour closely controlled in the ranges 0 to2500 ppm and 5 to 15 mb respectively, at flow rates of up to10 1 min^-1, to each four leaf chambers. The leaf temperatureis controlled to ±0.5 °C and, with a light intensityof 0.3 cal cm^-2 min^-1 visible radiation (0.4 to 0.7 µm)leaf temperature can be maintained at 17.5 °C.The apparatusused to measure the concentration differences between the watervapour and CO₂ entering and leaving the leaf chamber (used tocalculate transpiration, photosynthetic, and respiration rates)is described in detail.Results of tests, which show the necessityfor mounting a fan within the leaf chamber, are reported.Typicallight- and CO₂-response curves are given for kale leaves (Brassicaoleracca var. acephala) and an attempt is made to quantify theerrors in the measurement of photosynthesis and transpiration.     

Influence of pH upon the Warburg Effect in Isolated Intact Spinach Chloroplasts: II. Interdependency of Glycolate Synthesis upon pH and Calvin Cycle Intermediate Concentration in the Absence of Carbon Dioxide Photoassimilation

The light-dependent synthesis of glycolate derived from fructose 1,6-diphosphate, ribose 5-phosphate, or glycerate 3-phosphate was studied in the intact spinach (Spinacia oleracea) chloroplasts in the absence of CO(2). Glycolate yield increased with an elevation of O(2), pH, and the concentration of the phosphorylated compound supplied. No pH optimum was observed as the pH was increased from 7.4 to 8.5. The average maximal rate of glycolate synthesis was 50 mumoles per milligram chlorophyll per hour while the highest rate observed was 92 with 2.5 mm fructose 1,6-diphosphate in 100% O(2). The highest yields of glycolate synthesized from fructose 1,6-diphosphate, ribose 5-phosphate, or glycerate 3-phosphate were 0.14, 0.24, and 0.30, respectively, on a molar basis.