Optimal Control of Gas Exchange during Drought: Empirical Evidence

The optimal regulation model by Mäkelä, Berningerand Hari (Annals of Botany 77: 461–467, 1996) was appliedto data for photosynthesis and transpiration of Scots pine duringa 22-d drought period. There was a clear decrease in photosynthesisand transpiration during that period. The agreement betweenmodel and photosynthesis data was good. The residuals of photosynthesiswere not systematic with respect to temperature, irradianceor water vapour deficit. However, the model initially overestimatedtranspiration by 50%, although there was a clear linear relationshipbetween measured and estimated values. The results suggest thatthere was no decrease in photosynthetic capacity during theperiod, but a decrease in stomatal conductance was responsiblefor the changes in photosynthesis and transpiration. The observationsare similar to results in the literature. Transpiration; photosynthesis; stomatal conductance; drought; Pinus sylvestris     

The Effect of Dio-9 on Photosynthesis and Ion Transport in Nitella, Tolypella, and Hydrodictyon

The effect of Dio-9, on photosynthesis and active and passiveion transport at the plasmalemma has been investigated in Nitellatranslucens, Tolypella intricata, and Hydrodictyon africanum.The active K influx and the coupled active Na efflux were moreinhibited by this inhibitor of energy transfer in phosphorylationthan was photosynthesis. The active Cl influx, the associateddownhill cation influxes, and passive ion fluxes were inhibitedby Dio-9, to a smaller extent than was photosynthesis. Cl influxin the light was often stimulated at concentrations of Dio-9,which inhibited photosynthesis. It was concluded that the activeK influx and Na efflux require ATP, while the active Cl influxdoes not. Possible links between the Cl influx and electrontransport and intermediates of photophosphorylation, and possibleinhibition by Dio-9 of the transport ATPase in the plasmalemmaare discussed.     

Photosynthesis and Light Activation of Ribulose 1,5-bisphosphate Carboxylase in the Presence of Starch

Limitation of photosynthesis and light activation of ribulose,1,5-bisphosphate carboxylase (RuBPCO) were examined in the 5thleaf of seedlings of red clover (Trifolium pratense L. cv. Renova)for 5 d following an increase in photosynthetic photon fluxdensity (PPFD) from 200 to 550µmol quanta m^–2 s^–1.Net photosynthesis and its stimulation at 2.0 kPa O₂ initialactivity of rapidly extracted RuBPCO, standard activity of RuBPCOafter incubation of the extracts in the presence of CO₂, Mg²⁺,and inorganic phosphate and contents of soluble protein, starch,soluble sugars, and various photosynthetic metabolites weredetermined. Photosynthesis decreased and starch content increased.No decrease in photosynthesis was found if, when PPFD was increased,all leaves except the investigated 5th leaf were removed, suggestingthat the decrease in photosynthesis was due to accumulated carbohydrates.The stimulation of photosynthesis at 2.0 kPa O₂ did not decreaseand the ratio of the total foliar steady-state contents of triosephosphate to 3-phosphoglycerate increased suggesting that thedecrease in photosynthesis was not due to limiting inorganicphosphate in chloroplasts. Intercellular CO₂ partial pressureand RuBP content were not decreased. Nevertheless, the ratioof photosynthesis to initial RuBPCO activity decreased, suggestingthat the catalysis per active RuBPCO site was decreased. Theincrease in PPFD in the growth cabinet and the PPFD at whichleaves were preconditioned for 1 h, affected not only initialactivity but also the standard activity of RuBPCO. The resultssuggest that a varying proportion of RuBPCO was bound to membranesand was contained in the insoluble fraction of the extracts.A comparison of photosynthesis with extracted RuBPCO activitysuggested that membrane bound RuBPCO did not contribute to photosyntheticCO₂ fixation and that the binding and release to and from membranesmodulated actual RuBPCO activity in vivo. Key words: Photosynthesis, ribulose 1,5-bisphosphate carboxylase, starch     

Photosynthesis and Transpiration in Rice as Influenced by Soil Moisture and Air Humidity

The paper describes the effect of soil moisture content andair humidity on CO₂ exchange (P_N), CO₂ diffusion resistance(Cr) and transpiration (E) in four varieties of japonica rice(Oryza sativa L.). A decrease in soil moisture content reducedthe rate of photosynthesis to a varying degree in the varieties.Reduction in photosynthesis was attributed to increase in Cr.The effect of low soil moisture on photosynthesis and CO₂ diffusionwas further intensified by decrease in air humidity. By maintaininga high humidity in the air around the leaves however, the effectof soil moisture deficiency was reduced considerably, exceptin Rikuto Norin 21 which was very sensitive to soil-moisturedeficiency alone. Dryness of the air enhanced the transpirationrate, although the increase was relatively less in the plantsfacing a simultaneous water crisis at the root surface. In plantsgrowing under flooded conditions, a decrease in air humiditycaused a slight depression in P_N despite the simultaneous decreasein Cr. Oryza sativa L., rice, photosynthesis, transpiration, diffusion resistance, soil moisture, air humidity     

The Effect of Temperature on Photosynthesis of Ryegrass and White Clover Leaves

The rate of photosynthesis of leaves of perennial ryegrass (Loliumperenne L.) and white clover (Trifollum pratense L.) grown atdifferent temperatures was measured at a range of temperatures.There was a small effect of the temperature at which a leafhad grown on its photosynthetic rate, but a large effect ofmeasurement temperature, especially in bright light, where photosyntheticrates at 15°C were about twice those at 5°C. It appearsthat temperature could affect sward photosynthesis in the field.Ryegrass and clover had similar photosynthetic rates which respondedsimilarly to temperature. Lolium perenne L., ryegrass, Trifolium pratense L., white clover, photosynthesis, temperature, irradiance     

Variation in Net Photosynthesis, Rubisco Activity and Chloroplast Ultrastructure among Somatic Hybrids of Solanum tuberosum and S. brevidens

The effect of ploidy, parental chloroplast type and parentalnuclear genome dosage on net photosynthesis, Rubisco activityand chloroplast ultrastructure was studied among somatic hybridsof diploid S. brevidens and dihaploid S. tuberosum. An increasein nuclear ploidy resulted in an increase in net photosynthesisand specific leaf weight. There were no significant differencesin net photosynthesis or Rubisco activity between the hybridshaving different parental chloroplast type. Examination of thehexaploid hybrids indicated that Rubisco activity was affectedby nuclear-organelle genome incompatibility, the most affectedcombination being tuberosum chloroplast type with brevidensnuclear genome. Examination of chloroplast ultrastructure revealedwide variation in the size of chloroplasts, starch granules,plastoglobuli and in grana stacking among the hybrids and betweenfusion parents. Key words: Somatic hybrids, Solanum, net photosynthesis, Rubisco, chloroplast ultrastructure     

Photosynthesis and Photorespiration in Lolium multiflorum and Lolium perenne

The response of net photosynthesis to changing light-flux densityby leaves of Lolium multiflorum (S. 22) and L. perenne (S. 321)is more adequately described by current models when a term allowingfor photorespiration is included. The magnitude of this termwas determined from the changes in the slope of the light-responsecurves for net photosynthesis. A pseudo first-order rate-constantfor photorespiration, and a pseudo second-order rate-constantfor photosynthesis calculated by this technique for L. multiflorumwere found to be similar to corresponding parameters calculatedfrom light-compensation-point measurements using a simple modeldescribed by Brown (1969). The relative magnitudes of respirationand photosynthesis at light saturation for both Lolium specieswere similar to reported values for other temperate species(Lake, 1967). Two selection lines of L. perenne (S. 321) with contrastingdry-matter yields were found to have the same parameters forrespiration and photosynthesis.     

Stimulation of Photosynthesis in Uninfected Leaves of Rust-infected Leeks

Fourth leaves of healthy leek plants exhibit very low ratesof net photosynthesis which appear to be related to the veryslow growth rates of young leeks early in the season. A stimulation in the rate of net photosynthesis was found tooccur in uninfected leaves of leek plants infected with therust, Puccinia porri. This was accompanied by a reduction inthe rate of photorespiration. Although the mechanisms underlyingthis response are not known, it may be instructive to comparethese results with those obtained from partial defoliation experiments.Increased photosynthetic activity in uninfected leaves may enablethe infected plant to maintain a functional shoot: root equilibrium. Allium porrum L., leek, Puccinia porri, leek rust, stimulation, photosynthesis, reduction, photorespiration     

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     

Dark Respiration of Winter Wheat Crops in Relation to Temperature and Simulated Photosynthesis

The dark respiration of shoots (measured between March and anthesisin mid-June) and of ears (measured between anthesis and maturityat end of July) of winter wheat crops, grown in 1982 and 1985under different nitrogen application and irrigation conditions,was determined in the field. The respiration rate of 126 averagesof four samples was measured hourly for a 12–14-h darkperiod including the night. Respiration (expressed per unitdry mass) generally declined through the season for both shootsand ears. The average rate of respiration obtained on the samenight was greater for fertilized and irrigated crops, comparedwith unfertilized and droughted crops. The relationship betweenthe measured respiration and photosynthesis, simulated usinga modified version of the model developed by Spitters (1986),was analysed. This revealed that: (a) Shoot respiration was less well correlated with photosynthesisfrom the day preceding measurement than with the average ofthe photosynthesis from the two days preceding measurement. (b) The constants relating shoot respiration to total crop photosynthesisper unit crop mass and ear respiration to total crop photosynthesisper unit ear mass had similar values. This suggests that allgrowth respiration takes place in the ears at the end of theseason. (c) Crop growth respiration consumes about 35% of assimilatebefore anthesis, and that growth respiration of the ear consumesabout 40% of assimilate at the end of the season. (d) No significant effect of treatment on the relationship betweenrespiration and photosynthesis was detected, suggesting thatthe observed effect of treatment on respiration is due entirelyto differences in photosynthesis. Triticwn aestivum var. Avalon, winter wheat, dark respiration, growth coefficient, photosynthesis model, nitrogen nutrition, irrigation     

Validation of a Photosynthesis Model through the Use of the CO2Balance of a Greenhouse Tomato Canopy

Several leaf photosynthesis models were developed from wellcontrolled experiments in growth chambers. However, only a fewhave been validated under greenhouse conditions for their quantitativeand qualitative adequacy. In this paper, rates of net photosynthesisfor a tomato crop (Lycopersicon esculentum Mill) were measuredin a semi-commercial greenhouse (615 m³) for a significant timeperiod. Concomitant measurements of climatic conditions andLAI were used for simulation of net photosynthesis using theTOMGRO model which integrates Acock's model for photosynthesiscalculations. From simulations and from sensitivity analysis,the prediction of net photosynthesis appeared to be very sensitiveto the quantum use efficiency. The Acock model with originalparameters underestimated the net photosynthesis rate, but anincrease in the quantum use efficiency by 10% gave a good fit.In an effort to generalize the validity of the model, a residualanalysis was performed and showed a systematic bias relatedto light intensity intercepted by the canopy. The Marquardtalgorithm was used to adjust our data to the model but did noteliminate residual heterogeneity of variance with new parametervalues. On the basis of collected data, the criteria of goodnessof fit used showed that the photosynthesis model is inadequatein describing the CO₂-balance of the greenhouse agrosystem.However, it was determined that it could be used as a submodelwithin a more complex model for predicting growth and development.Copyright 1999 Annals of Botany Company Greenhouse, CO₂-balance, photosynthesis, TOMGRO model, Acock's model, residuals, tomato Lycopersicon esculentum Mill.     

Microclimate, Canopy Structure and Photosynthesis in Canopies of Three Contrasting Temperate Forage Grasses: III. Canopy Photosynthesis, Individual Leaf Photosynthesis and the Distribution of Current Assimilate

The rates of canopy and individual leaf photosynthesis and ¹⁴Cdistribution for three temperate forage grasses Lolium perennecv. S24, L. perenne cv. Reveille and Festuc'a arundinacea cv.SI70 were determined in the field during a summer growth period.Canopy photosynthesis declined as the growth period progressed,reflecting a decline in the photosynthetic capacity of successiveyoungest fully expanded leaves. The decline in the maximum photosyntheticcapacity of the canopies was correlated with a decline in theirquantum efficiencies at low irradiance. Changes in canopy structureresulted in changes in canopy net photosynthesis and dark respiration.No clear relationships between changes in the environment andchanges in canopy net photosynthesis and dark respiration wereestablished. The relative distributions of ¹⁴C in the shootsof the varieties gave a good indication of the amount of drymatter per ground area in the varieties.     

Canopy Photosynthesis of Tomato, Cucumber and Sweet Pepper in Greenhouses: Measurements Compared to Models

Two models for canopy photosynthesis (modified versions of thoseof Acock et al. , 1978 and of Thornley, 1976) were examinedby comparison with experimental photosynthesis data of cucumber(Cucumis sativus L.), sweet pepper (Capsicum annuum L.) andtomato (Lycopersicon esculentum Mill.). The data were obtainedin six large-scale, long-term, semi-commercial cultivationsin greenhouses (Nederhoff and Vegter, 1994). Measured environmentalconditions and measured LAI were input to the model. The emphasiswas on the models' sensitivity to the prevailing CO₂ concentration. The (modified) Acock model with 'standard' (originally published)parameters underestimated the photosynthesis rate. This modeltuned to one of our experimental data sets did not fit verywell to the other data sets. As expected, if the model was tunedto each particular data set, it was fairly in agreement withthe measurements, but the fitted parameter values were sometimesquestionable. With the (modified) Thornley model it was obligatoryto estimate or tune the light extinction. The model performedreasonably if all parameters were tuned and also if only thelight extinction was tuned. The modified models were considered usable for practical applications,after parameter tuning. As the sensitivity to CO₂ was not alwaysequal among the models and the measurements, care should betaken when applying the models for CO₂ supply control.Copyright1994, 1999 Academic Press Canopy photosynthesis, Capsicum annuum L., carbon dioxide, cucumber, CO₂, Cucumis sativus L., glasshouse, greenhouse, Lycopersicon esculentum Mill., measurements, model, sweet pepper, tomato     

Dry-matter Production and Photosynthesis in Pine Seedlings

Growth analysis and photosynthesis measurements were carriedout on first-year seedlings of Pinus radiata, P. contorta, andP. nigra. P. sylvestris was also included in two growth-analysisexperiments. There appeared to be no difference in relativegrowth-rate (RGR) between the species mentioned, except betweenP. radiata and P. nigra. It was found that when the level ofmineral nutrition was high, P. radiata had a higher RGR thanP. nigra and that the reverse was true at low mineral nutrientlevels. There was no difference in net assimilation rate (NAR)between the species, but NAR appeared to increase and decreasewith mineral nutrient supply. Net photosynthesis per unit of leaf was somewhat higher in P.radiata than in P. contorta; P. nigra had a lower photosyntheticrate than either P. radiata or P. contorta.     

The Responses of Net Photosynthesis to Vapour Pressure Deficit and CO2 Concentration in Spartina townsendii (sensu lato), a C4 Species from a Cool Temperate Climate

As the initial part of a detailed study of photosynthetic CO₂assimilation in the temperate C₄ grass, Spartina townsendii,the responses of net photosynthesis to the leaf-air vapour pressuredeficit (VPD) and to CO₂ concentration are examined. Water vapourand CO₂ exchange for single attached leaves were measured undercontrolled-environment conditions in an open gas-exchange system.The responses of net photosynthesis, stomatal resistance (r_s),and residual resistance (r_r) to vapour pressure deficit(VPD)and CO₂ concentration under a range of light and temperatureconditions are reported. Net photosynthesis was insensitiveto increase in the VPD up to 1.0 kPa, but beyond this valuenet photosynthesis decreased with further increase in VPD asa result of an increase in r_s. The residual resistance was notaffected by VPD under any of the conditions examined. Net photosynthesisresponded linearly to increase in the CO₂ concentration in theexternal air (C_a up to the normal atmospheric concentrationwhere there was a sharp change in the response, net photosynthesisbeing independent of any further increase in C_a. Differencesbetween the response curves observed here and in other studiesare discussed and the possible reasons for these differencesare considered.     

Factors Controlling Induction of External Carbonic Anhydrase and Change in K?(CO2) of Photosynthesis in Chlorella regularis

Transfer of algal cells of Chlorella regularis from 3% CO₂ inair into ordinary air in the light increased external carbonicanhydrase (CA) activity as well as photosynthetic affinity forCO₂ by several-fold within 2 h. Since no noticeable differencewas observed in CA activity between intact cells and cell homogenates,CA seemed to be mainly localized on the cell surface. Changesin CA activity and K_?(CO₂) of photosynthesis were not observedin the dark. CA induction was 50%-inhibited by incubation with10 µM DCMU during adaptation of high-CO₂ cells to air,whereas it was considerably suppressed when high-CO₂ cells preincubatedwith DCMU in the light for 6 h or without DCMU in the dark for24 h were used. The change in K_?(CO₂) of photosynthesis wasonly slightly affected by DCMU. Uncoupler like carbonylcyanide-m-chlorophenyl-hydrazone(CCCP) and inhibitors of mitochondrial respiration (KCN plussalicylhydroxamic acid) suppressed CA induction during adaptationof high-CO₂ cells to low CO₂ conditions. These results suggest that photosynthesis is not essential forCA induction in Chlorella regularis when some amounts of photosyntheticproducts are previously stored in the cells and respirationis active. A decrease in K_?(CO₂) of photosynthesis during adaptationfrom high to low CO₂ was mostly independent on photosynthesis.However, light is essential for both phenomena. (Received July 16, 1990; Accepted January 21, 1991)     

Inhibition of photosynthesis in olive trees (Olea europaea L.) during water stress and rewatering

The effect of high levels of natural light on leaf photosynthesisin olive trees (Olea europaea L. var. Coratina), grown in potsoutdoors in the summer and subjected to water, stress, was studied.Net photosynthetic rates reached maximum values early in themorning in both control and stressed plants and subsequentlydeclined gradually. This inactivation of photosynthetic activitywas accompanied by changes in the fluorescence characteristicsof the upper intact leaf surface. The maximum fluorescence yield(Fp) and the ratio Fv/Fp decreased at midday especially in water-stressedplants, but the initial fluorescence (Fo) rose to a maximumvalue at midday and declined again in the afternoon. In controlplants the values of maximum fluorescence Fp and the ratio Fv/Fpincreased again in the afternoon and had recovered almost completelyby 8 p.m. as the leaf water potential recovered. In stressedplants this diurnal recovery was not complete, so that the photosyntheticrates and the ratio Fv/Fp declined gradually during the developmentof water stress. These results indicate that in olive treessubjected to severe water stress the non-stomatal componentof photosynthesis was affected and perhaps a light-dependentinactivation of the primary photochemistry associated with photosystemII (PSII) occurred. Four to five days after rewatering severelystressed plants, the predawn leaf water potential, net photosyntheticrates and chlorophyll fluorescence indices recovered only partially. Key words: Olea europaea, photosynthesis, water stress, chlorophyll a fluorescence, inhibition of photosynthesis     

Dynamics of Vertical Leaf Nitrogen Distribution in a Vegetative Wheat Canopy. Impact on Canopy Photosynthesis

The development of vertical canopy gradients of leaf N has beenregarded as an adaptation to the light gradient that helps tomaximize canopy photosynthesis. In this study we report thedynamics of vertical leaf N distribution during vegetative growthof wheat in response to changes in N availability and sowingdensity. The question of to what extent the observed verticalleaf N distribution maximized canopy photosynthesis was addressedwith a leaf layer model of canopy photosynthesis that integratesN-dependent leaf photosynthesis according to the canopy lightand leaf N distribution. Plants were grown hydroponically attwo amounts of N, supplied in proportion to calculated growthrates. Photosynthesis at light saturation correlated with leafN. The vertical leaf N distribution was associated with thegradient of absorbed light. The leaf N profile changed duringcrop development and was responsive to N availability. At highN supply, the leaf N profiles were constant during crop development.At low N supply, the leaf N profiles fluctuated between moreuniform and steep distributions. These changes were associatedwith reduced leaf area expansion and increasing N remobilizationfrom lower leaf layers. The distribution of leaf N with respectto the gradient of absorbed irradiance was close to the theoreticaloptimum maximizing canopy photosynthesis. Sensitivity analysisof the photosynthesis model suggested that plants maintain anoptimal vertical leaf N distribution by balancing the capacityfor photosynthesis at high and low light. Copyright 2000 Annalsof Botany Company Canopy photosynthesis, leaf nitrogen distribution, nitrogen, Triticum aestivum L, wheat     

Extracellular Release of Organic Matter from Two Freshwater Diatoms

The ¹⁴C-labelled extracellular materials released from culturesof Synedra acus and Stephanodiscus hantzschii were separatedby paper chromatography. The major components were identifiedand their rates of release measured. Stephanodiscus in axenicculture released the same extracellular materials under optimumlight conditions as did the natural population from which thediatom was isolated. The major extracellular product of Stephanodiscuswas glycollate; polysaccharide and amino acids were also released.The major extracellular product of Synedra was polysaccharide;amino acids were also released, but no glycollate. Under lightintensities so high as to inhibit photosynthesis the arraysof extracellular substances were unchanged, but some rates ofrelease were reduced. The array of products and the rates ofrelease from Stephanodiscus in darkness are quite differentfrom extracellular release during photosynthesis. Glycollaterelease from Stephanodiscus is greatest when the cultures areyoung and growing rapidly, older cultures release less.     

The Structure of the Mesophyll of Flag Leaves in Three Triticum Species

Flag leaves of Triticum urartu, T. monococcum and T. aestivumcv. Professeur Marchal were examined by light and electron microscopyand by separating cells to determine whether differences inleaf anatomy could be related to known differences in theirlight-saturated rates of photosynthesis. Mesophyll cells fromthe three species were lobed and orientated with their longaxis parallel to the veins. The longest, most-lobed cells flankedthe sclerenchyma associated with the veins. Mean cell dimensionswere greatest in Professeur Marchal, but there was no significantdifference in the ratio of the mesophyll cell surface area tocell volume amongst the three species. Flag leaves of T. urartushowed the highest rates of photosynthesis and were also thethickest, with closely-spaced veins from which many of the mesophyllcells radiated. These flag leaves also had significantly more(21.9 per cent) air-filled space, and the highest ratio (15.2)of mesophyll cell surface exposed to this air-filled space perunit leaf area. Ways in which these anatomical characteristicsmay contribute to the higher rate of photosynthesis are discussed. Triticum urartu, Triticum monococcum, Triticum aestivum, flag leaves, morphology, mesophyll