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.     

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.     

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.     

A Cuvette Design for Measurement of Ethylene Production and Carbon Dioxide Exchange by Intact Shoots under Controlled Environmental Conditions

A cuvette is described for simultaneous measurement of ethylene production and CO₂ fixation by intact shoots under controlled environmental conditions. This design overcomes potential problems associated with closed systems conventionally used for studies on ethylene production, allowing accurate determination of rates of ethylene production in plants exposed to different environmental conditions.     

Carbon Dioxide Fixation and Ribulose-1, 5-bisphosphate Carboxylase Activity in Intact Leaves of Sugar Beet Plants Exposed to Salinity and Water Stress

The influence of salinity in the growing media on ribulose-1,5-bisphosphate (RuBP) carboxylase and on CO₂ fixation by intactsugar beet (Beta vulgaris) leaves was investigated. RuBP carboxylase activity was mostly stimulated in young leavesafter exposure of plants for 1 week to 180 mM NaCl in the nutrientsolution. This stimulation was more effective at the higherNaHCO₂ concentrations in the reaction medium. Salinity also enhanced CO₂ fixation in intact leaves mostlyat rate-limiting light intensities. A 60 per cent stimulationin CO₂ fixation rate was obtained by salinity under 450 µEm^–2 s^–1. At quantum flux densities of 150 µEm^–2 s^–1 (400–700 nm) this stimulation was280 per cent. Under high light intensities no stimulation bysalinity was found. In contrast, water stress achieved by directleaf desiccation or by polyethylene glycol inhibited enzymeactivity up to fourfold at –1.2 MPa. Beta vulgaris, sugar beet, ribulose-1, 5-bisphosphate carboxylase, salt stress, water stress, carbon dixoide fixation, salinity     

Changes in Transpiration, Net Carbon Dioxide Assimilation and Leaf Water Potential Resulting from Application of Hydrostatic Pressure to Roots of Intact Pepper Plants

Hydrostatic pressures varying from 0 to 6.0 bar were applied to roots of intact Capsicum annuum L. cv. California Wonder plants growing in nutrient solution and the rates of transpiration, and net CO₂ assimilation, apparent compensation point and leaf water potential measured. Increasing the pressure on the roots of plants with roots in solution with either -0.5 or -5.0 bar osmotic potential with 1 bar increments resulted in a decrease in transpiration. With the application of 1 or 2 bar pressure the rate of transpiration returned to near or above the original rate. An application of 3 or 4 bar pressure reduced the rate of transpiration of all plants. The transpiration of plants with roots in solution with -0.5 bar osmotic potential remained at the reduced rate for as long as these pressures were maintained. The transpiration of plants with roots in solution with -5.0 bar was only temporarily suppressed at these pressures. Changing the applied pressure from 3 or 4 bar to 0 resulted in a rapid increase in transpiration which lasted approximately 15 minutes. This was followed by a decrease in transpiration to a rate lower than before the pressure was applied. The pattern of response was similar for plants at low or high light intensity or at normal or low CO₂ concentrations. When leaf diffusive resistance was 6.0 s cm^?1 or greater, changes in net CO₂ assimilation were similar to those of transpiration. The apparent CO₂ compensation point increased as pressure was applied and decreased with a release in pressure. Leaf water potential increased with an increase in pressure and decreased with a decrease in pressure. The changes in leaf water potential were frequently but not always proportional to changes in pressure. It is postulated that the respouses noted were due to changes in resistance to flow of water from xylem terminals through the mesophyll cells and stomatal cavities to the atmosphere.     

The Critical Oxygen Pressures for Respiration in Intact Plants

Two methods for determining critical respiratory oxygen pressure in whole plants are described. By a polarographic method involving the use of cylindrical platinum electrodes the following critical oxygen pressures for root respiration were found: Rice (cv. Norin 36). 0.024 atm: Rice (cv. Norm 37). 0.026 atm: Eriophorum angustifolium. 0.02 atm. These values contrast markedly with those obtained in vitro, and support earlier criticisms of in vitro measurements: they call into question the use of such data in the modelling of root aeration. When the results were assessed by an electrical analogue system, it was concluded that the respiratory activity in the intact root does not follow the normally accepted hyperbolic relationship with oxygen partial pressure. The experimental data were simulated most closely by assuming the critical oxygen pressure to be a function of respiratory responses in the low porosity (high diffusional impedance) tissues of the root meristem and stele, and respiratory activity in the moderately porous root cortex to be unaffected at values greater than 0.001 atm. A critical oxygen pressure of 0.025–0.04 atm for E. angustifolium was found from analyses of the gas phase oxygen in the leaves of whole plants after submergence in the dark. It was concluded that the higher value found by this method was most likely a function of respiratory responses in root tissue remote from the leaf and should not be regarded as the critical oxygen pressure for leaf respiration. The form of the oxygen concentration vs. time plot again suggested a very much lower critical oxygen pressure for certain of the plant tissues.     

Effect of Light Intensity, Carbon Dioxide Concentration, and Leaf Temperature on Gas Exchange of Spray Carnation Plants

The rates of CO₂ assimilation by potted spray carnation plants(cv. Cerise Royalette) were determined over a wide range oflight intensities (45–450 W m^–2 PAR), CO₂ concentrations(200–3100 vpm), and leaf temperatures (5–35 °C).Assimilation rates varied with these factors in a way similarto the response of single leaves of other temperate crops, althoughthe absolute values were lower. The optimal temperature forCO₂ assimilation was between 5 and 10 °C at 45 W m^–2PAR but it increased progressively with increasing light intensityand CO₂ concentration up to 27 °C at 450 W m^–2 PARand 3100 vpm CO₂ as expressed by the equation TOpt = –6.47-h 2.336 In G + 0.031951 where C is CO₂ concentration in vpmand I is photo-synthetically active radiation in W m^–2.CO₂ enrichment also increased stomatal resistance, especiallyat high light intensities. The influence of these results on optimalization of temperaturesand CO₂ concentrations for carnation crops subjected to dailylight variation, and the discrepancy between optimal temperaturesfor growth and net photosynthesis, are discussed briefly     

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.     

Photosynthetic Acclimation to Temperature in the Desert Shrub, Larrea divaricata: I. Carbon Dioxide Exchange Characteristics of Intact Leaves

Larrea divaricata, a desert evergreen shrub, has a remarkable ability to adjust its photosynthetic temperature response characteristics to changing temperature conditions. In its native habitat on the floor of Death Valley, California, plants of this C₃ species when provided with adequate water are able to maintain a relatively high and constant photosynthetic activity throughout the year even though the mean daily maximum temperature varies by nearly 30 C from winter to summer. The temperature dependence of light-saturated net photosynthesis varies in concert with these seasonal temperature changes whereas the photosynthetic rate at the respective optimum temperatures shows little change.

Experiments on plants of the same age, grown at day/night temperatures of 20/15, 35/25, and 45/33 C with the same conditions of day length and other environmental factors, showed a similar photosynthetic acclimation response as observed in nature. An analysis was made of a number of factors that potentially can contribute to the observed changes in the temperature dependence of net CO₂ uptake at normal CO₂ and O₂ levels. These included stomatal conductance, respiration, O₂ inhibition of photosynthesis, and nonstomatal limitations of CO₂ diffusive transport. None of these factors, separately or taken together, can account for the observed acclimation responses. Measurements under high saturating CO₂ concentrations provide additional evidence that the observed adaptive responses are primarily the result of changes in intrinsic characteristics of the photosynthetic machinery at the cellular or subcellular levels. Two apparently separate effects of the growth temperature regime can be distinguished: one involves an increased capacity for photosynthesis at low, rate-limiting temperatures with decreased growth temperature, and the other an increased thermal stability of key components of the photosynthetic apparatus with increased growth temperature.

     

Glycolate Excretion and the Oxygen to Carbon Dioxide Net Exchange Ratio during Photosynthesis in Chlamydomonas reinhardtii

Chlamydomonas reinhardtii cells were grown in high (5% v/v) or low (0.03% v/v) CO₂ concentration in air. O₂ evolution, HCO₃⁻ assimilation, and glycolate excretion were measured in response to O₂ and CO₂ concentration. Both low- and high-CO₂-grown cells excrete glycolate. In low-CO₂-grown cells, however, glycolate excretion is observed only at much lower CO₂ concentrations in the medium, as compared with high-CO₂-adapted cells. It is postulated that the activity of the CO₂-concentrating mechanism in low-CO₂-grown cells is responsible for the different dependence of glycolate excretion on external CO₂ concentration in low- versus high-CO₂-adapted cells.     

Carbon Dioxide Exchange and Acidity Levels in Detached Pineapple, Ananas comosus (L.), Merr., Leaves during the Day at Various Temperatures, Oxygen and Carbon Dioxide Concentrations

The effects of temperature, O₂, and CO₂ on titratable acid content and on CO₂ exchange were measured in detached pineapple (Ananas comosus) leaves during the daily 15-hour light period. Comparative measurements were made in air and in CO₂-free air. Increasing the leaf temperature from 20 to 35 C decreased the total CO₂ uptake in air and slightly increased the total CO₂ released into CO₂-free air. Between 25 and 35 C, the activation energy for daily acid loss was near 12 kcal mol⁻¹, but at lower temperatures the activation energy was much greater.     

Concurrent Measurements of Oxygen and Carbon Dioxide Exchange during Lightflecks in Maize (Zea mays L.)

Leaves of maize (Zea mays L.) were enclosed in a temperature-controlled cuvette under 35 Pa (350 [mu]bars) CO2 and 0.2 kPa (0.2%)O2 and exposed to short periods (1-30 s) of illumination (light-flecks). The rate and total amount of CO2 assimilated and O2 evolved were measured. The O2 evolution rate was taken as an indicator of the rate of photosynthetic noncyclic electron transport (NCET). In this C4 species, the response of electron transport during the lightflecks qualitatively mimicked that of C3 species previously tested, whereas the response of CO2 assimilation differed. Under short-duration lightflecks at high photon flux density (PFD), the mean rate of O2 evolution was greater than the steady-state rate of O2 evolution under the same PFD due to a burst of O2 evolution at the beginning of the lightfleck. This O2 burst was taken as indicating a high level of NCET involved in the buildup of assimilatory charge via ATP, NADPH, and reduced or phosphorylated metabolites. However, as lightfleck duration decreased, the amount of CO2 assimilated per unit time of the lightfleck (the mean rate of CO2 assimilation) decreased. There was also a burst of CO2 from the leaf at the beginning of low-PFD lightflecks that further reduced the assimilation during these lightflecks. The results are discussed in terms of the buildup of assimilatory charge through the synthesis of high-energy metabolites specific to C4 metabolism. It is speculated that the inefficiency of carbon uptake during brief light transients in the C4 species, relative to C3 species, is due to the futile synthesis of C4 cycle intermediates.     

In-Phase Cycling of Photosynthesis and Conductance at Saturating Carbon Dioxide Pressure Induced by Increases in Water Vapour Pressure Deficit

Bunce, J. A. 1987. In-phase cycling of photosynthesis and conductanceat saturating carbon dioxide pressure induced by increases inwater vapour pressure deficit.—J. exp. Bot. 38: 1413–1420. The leaf to air water vapour deficit was increased suddenlyfrom about 1·0 to 2·5 IcPa for single leaves ofsoybean (Glycine max L. Merr.) plants held at 30 °C, 2·0mmol m ^–2 s^–1 photosynthetic photon flux density(PPFD) and carbon dioxide pressures saturating to photosynthesis.After a lag of about 10 min, photosynthetic rate and stomatalconductance to water vapour began to decrease, and then cycledin phase with each other. The period of the cydes was about20 min. During these cycles the substomatal carbon dioxide pressurewas constant in the majority of leaves examined, and was alwaysabove saturation for photosynthesis. Epidermal impressions showedthat most stomata changed in aperture during the cycles, andthat very few were ever fully closed. Water potential measuredon excised discs changed by at most 0·1 MPa from theminima to the maxima in transpiration rate. In contrast, forleaves of sunflower (Helianthus animus L.) grown at low PPFD,the increase in VPD led to leaf wilting and decreased photosynthesis,followed by recovery of turgor and photosynthesis as stomatalconductance began to decrease. In these leaves photosynthesisand conductance then cycled approximately 180° out of phase.It is suggested that in soybeans decreased leaf conductanceinduced by high VPD provided a signal which decreased the rateof photosynthesis at carbon dioxide saturation by a mechanismthat was not related to a water deficit in the mesophyll. Key words: Photosynthesis, stomatal conductance, cycling, vapour pressure deficit     

Enzyme Activities Associated with Carbon Dioxide Exchange in Illuminated Leaves of Hordeum vulgare L.: II. Effects of External Concentrations of Carbon Dioxide and Oxygen

Plants grown in a high carbon dioxide environment (< 1 percent) were found to have increased levels of RuDP carboxylase,and suppressed activities of catalase, glycollate oxidase, andnitrate reductase, enzymes all associated with the peroxisome.Similarly, plants grown in low oxygen concentrations showedsuppressed activities of the peroxisomal enzymes. However, underthese conditions RuDP carboxylase activity was also suppressed.These results further suggest that nitrate reductase activityis associated with photorespiration.