Some Effects of Light Intensity, Daylength and Temperature on Growth of Fruiting and Non-fruiting Watermelon (Citrullus lanatus)

Plants of watermelon [Citrullus lanatus(Thunb.) Matsum. &Nakai, cv. Early Yates] were grown for up to 3 months aftergermination in controlled environment cabinets, and variousaspects of vegetative growth and fruit development were measured.Effects of light intensity were studied by comparing growthat 8, 16 and 32 klx at constant temperature and daylength (25^°C, 14 h). Effects of daylength were studied by comparing8, 14 and 24 h at constant light intensity and temperature (32klx, 25 ^°C), and effects of tem perature were studied bycomparing 20^°, 25^°, 30^°, 35^° and 40 ^°C atconstant light intensity and day- length (32 klx, 14 h). Withincreasing light intensity and daylength lateral growth waspromoted whereas main shoots were less affected. Increase intemperature above 25 ^°C resulted in longer main shoots andprolific lateral growth, due both to more and to longer laterals.Environmental differences had little effect on internode lengthbut did affect the size of basal leaves. However, an increasein total leaf area at higher temperatures or with Continuouslight was mainly due to more leaves rather than larger leaves.The presence of developing fruit greatly reduced vegetativegrowth of plants. Main shoot length, lateral growth, numberof leaves, and even size of individual leaves, were all reduced.This reduction did not apply to d. wt of whole plants. Fruitingplants were very efficient, on a leaf area basis, in accumulatingd. wt. At 25 ^°C at the two higher light intensities with14 h days the presence of one developing fruit was inhibitoryto the setting of any subsequent fruit. With short days or lowlight, more fruits were set but they were small. With continuouslight or high temperature more than one fruit could developand they were large.     

Control of the Acclimation of Photosynthesis to Light and Temperature in Relation to Partitioning of Photosynthate in Developing Soybean Leaves

Photosynthetic acclimation was examined by exposing third trifoliolateleaves of soybeans to air temperatures of 20 to 30°C andphotosynthetic photon flux densities (PPFD) of 150 to 950µmolphotons m^–2 s^–1 for the last 3 d before they reachedmaximum area. In some cases the environment of the third leafwas controlled separately from that of the rest of the plant.Photosynthesis, respiration and dry mass accumulation were determinedunder the treatment conditions, and photosynthetic capacity,and dry mass and protein content were determined at full expansion.Photosynthetic capacity, the light-saturated rate of net carbondioxide exchange at 25°C and 34 Pa external partial pressureof carbon dioxide, could be modified between 21 and 35 µmolCO₂ m^–2 s^–1 by environmental changes after leaveshad become exporters of photosynthate. Protein per unit leafmass did not differ between treatments, and photosynthetic capacityincreased with leaf mass per unit area. Photosynthetic capacityof third leaves was affected by the PPFD incident on those leaves,but not by the PPFD on other leaves on the plant. Photosyntheticcapacity of third leaves was affected by the temperature ofthe rest of the plant, but not by the temperature of the thirdleaves. Photosynthetic capacity was linearly related to carbondioxide exchange rate in the growth regimes, but not to daytimePPFD. At high PPFD, and at 25 and 30°C, mass accumulationwas about 28% of the mass of photosynthate produced. At lowerPPFD, and at 20°C, larger percentages of the photosynthateproduced accumulated as dry mass. The results suggest that photosynthatesupply is an important factor controlling leaf structural growthand, consequently, photosynthetic acclimation to light and temperature. Key words: Glycine max (L.) Merr., photosynthesis, temperature acclimation, light acclimation, photosynthate partitioning     

Studies on the Expansion of the Leaf Surface: I. THE INFLUENCE OF TEMPERATURE

An investigation was made of the expansion of the leaf surfaceof cucumber at temperatures of 12°, 18°, 24°, and30°C. with two levels of visible radiation (40 and 80 cal.cm.^–2 day^–1). The relative rate of expansion ofthe leaf surface increased with temperature up to 24° butwas lower at 30° than at 24°. It was slightly greaterwith the higher than the lower level of radiation at the lowertemperatures only. This rate was the resultant of the rate ofunfolding of new leaves and the rate of expansion of the componentleaves. The rate of leaf production increased with increasingtemperature up to 24° and was constant there-after, butleaves unfolded from the terminal bud more rapidly with increasein temperature over the entire range. The rate of expansionof individual leaves was greatest at 24°, being less atboth lower and higher temperatures. Differences in this ratebetween temperatures increased in the order: cotyledon, leaf1, leaf 2. Leaf production and unfolding was greater with thehigher level of radiation but the expansion of individual leaveswas not influenced. These results suggested the following interpretation of theexpansion the leaf surface. Its potential rate is set by therate of unfolding of leaves from the terminal bud, which dependsmainly on the temperature and the rate of assimilation by theupper leaves and the terminal bud, the demand for assimilateexceeding the supply in this region. The demand for mineralsubstrates by the terminal bud is low and not influenced bya wide variation in potential supply. After unfolding from theterminal bud, the leaf provides most of its own supply of carbohydrateby assimilation and this can be met at a low level of radiation.Surplus assimilate is diverted to the roots and stems whichrespond much more to increased radiation than does the leafsurface. The demand for mineral substrates by expanding leaves,however, is high—the greater the number expanding at anytime the more likely is the demand by any one leaf to exceedthe supply. This leads to a reduction in the number of celldivision and, consequently, a reduced rate of expansion anda smaller leaf. The optimum level of any environmental factoris that at which the most effective compromise between theseconflicting processes is reached.     

Effects of Nitrogen on the Development and Growth of the Potato Plant. 1. Leaf Appearance, Expansion Growth, Life Spans of Leaves and Stem Branching

Potatoes (Solanum tuberosum L) were planted in pots in a temperature-controlledglasshouse to collect data on the rate of leaf apearance, leafexpansion, apical lateral branching and active life spans ofleaves The treatments consisted of three rates of nitrogen supply,i e the NI treatment with 2 5 g N per pot and the N2 and N3treatments with 8 and 16 g N per pot, respectively The rate of leaf appearance was 0·53 leaves d^–1(one leaf per 28 °C d) and was negligibly affected by nitrogensupply The rate of leaf expansion was related to leaf numberand nitrogen supply The areas of mature leaves increased withleaf number on the main stem to reach a maximum for leaf numbers12–14, and declined for higher leaf numbers Leaves onapical lateral branches declined in mature area with increasein leaf number The expansion rate of leaves was the dominantfactor that determined the mature leaf area, irrespective ofleaf number and nitrogen treatment The smallest leaves wereobserved at the lowest rate of nitrogen supply Nitrogen promotedapical branching and hence the total number of leaves that appearedon a plant The proportion of total leaf area contributed byleaves on apical branches increased with time and nitrogen supply Active life span, i e the period of time between leaf appearanceand yellowing of the leaf, showed a similar relation to leafnumber as mature leaf area, at least in qualitative terms Leavesof the N3 treatment showed systematically longer life spansthan leaves of the NI and N2 treatment in the order of 3 weeksThe number of main stem leaves was not affected by nitrogensupply Potato, Solanum tuberosum L, leaf development, leaf extension, plant structure, nitrogen nutrition     

Soyabean Stem In Vivo Nitrate Reductase Activity

Stem from three- and four-week-old Soyabean [Glycine max (L.)Merr. cv. Tracy] plants reduced from 0.3 to 0.7 µmol nitrateh^–l g^–l f. wt. Leaf activity was 4.7–7.6 µmolnitrate h^–l g^–l f. wt. Outer stem was two to fourtimes more active at reducing nitrate than was inner stem. Plantnitrate nutrition had a strong effect upon the ratio of activitypresent in stem and leaf. More nitrate increased the proportionpresent in leaves. Glycine max L., soyabean, nitrate assimilation, nitrogen metabolism, Rhizobium japonicum     

The Growth and Development of Simulated Swards of Perennial Ryegrass: I. Leaf Growth and Dry Weight Change as Related to the Ceiling Yield of a Seedling Sward

The leaf growth, tiller production, light interception, anddry weight increase of a simulated sward of S24 perennial ryegrass(Lolium perenne) were followed during the development of thesward from a collection of two-leaved seedlings to a closedcanopy with an LAI of 23, of which 15 consisted of green leaflaminae. The dry weight of live shoots increased exponentiallyat first, but then entered a long linear phase of increase.This was equivalent to a crop growth rate of 200 Kg ha^–1day^–1 and a conversion efficiency of radiant energy (400–700nm) of 7.2 per cent. Towards the end of the growth period therate of increase of live shoots declined rapidly to zero anda ceiling yield was reached equivalent to 10 metric tons ha^–1.Leaf growth continued at a high rate, but was equalled by therate of leaf death, so that the weight of live leaf tissue remainedconstant. By this time the swards had achieved a stable tillerpopulation (about 1 cm^–1), each tiller bore a constantnumber of live leaves (about three), and the length of eachnewly expanded leaf equalled the length of the old leaf it replaced(about 70 cm). The swards were grown in Perlite so that in theabsence of soil fauna dead leaves accumulated at the base ofthe sward where, after 12 weeks, they accounted for 19 per centof the total weight of dry matter produced.     

Studies on the Expansion of the Leaf Surface: II. THE INFLUENCE OF LIGHT INTENSITY AND DAYLENGTH

The parts played by constant amounts of visible radiation perday and its two components—daylength and intensity—ininfluencing the growth of Cucumis sativus have been investigated.The amount of radiation per day had a far greater influencethan either of its components per se. Nevertheless, small significanteffects of photoperiod were found, leaf expansion and dry weightincrease being greatest at daylengths between 10 and 15 hr.rather than with longer days which, with similar daily totals,would be expected to give the greatest amounts of assimilation. Rates of leaf production and appearance were greatest with thehighest amounts of radiation, but the rates of expansion ofindividual leaves and their maximum areas were greatest withintermediate amounts of radiation. This response resulted inan optimum curve relating the leaf surface and the dry weightattained after a given period to radiation. The amount of radiationgiving the maximum leaf surface and dry weight decreased withage and with external nutrient supply, but at any one age washigher for increase in dry weight than for increase in leafsurface; stem and root tissues responded more to high radiationthan did the leaf surface. The net assimilation rate was a linearfunction of visible radiation over the range of 15–120cal. cm.^-2 day^-1 explored, the highest value of radiation usedrepresenting the intensity at which photosynthesis would beexpected to be maximal over a 12–15 hr. day. The inhibitory effect of high radiation on leaf expansion andthe resultant influence on the growth of the plant are explainedin terms of the number and intensity of ‘sinks’for carbohydrate and mineral nutrients within the plant.     

Curd Initiation in the Cauliflower: I. JUVENILITY

Hand, D. J. and Atherton, J. G. 1987. Curd initiation in thecauliflower. I. Juvenility.—J. exp. Bot. 38: 2050–2058. Four cauliflower (Brassica oleracea var. botrytis L.) cultivarswere screened for differences in juvenility, measured as thephase of insensitivity to vernalization. Juvenility persisteduntil the initiation of a critical number of leaves which sharplydefined transition to the sensitive, mature form at 13 to 15leaves in cv. Perfection and at 17 to 19 leaves in cv. WhiteFox. Preliminary investigation showed transition in cv. AlphaCliro to occur between 9 and 18 leaves initiated and in cv.Dole after 19 leaves. Leaf number was a stable marker of theend of juvenility in plants grown under different light conditions,whereas time, leaf area and leaf dry weight were not. Leaf numberwas linearly related to log whole shoot dry weight. The rateof leaf initiation in plants of cv. Perfection growing duringthe juvenile phase was approximately one third that of plantsin the mature phase, when measured on a thermal time base. Chilling mature, vegetative plants at 5 °C for 28 d advancedcurd initiation by up to 35 leaves in cv. Perfection; 27 leavesin cv. White Fox; 27 leaves in cv. Alpha Cliro and 21 leavesin cv. Dok, compared with plants grown continuously at 20 °C. Key words: Cauliflower, vernalization, juvenility     

The Effect of Shade During Leaf Expansion on Photosynthesis by White Clover Leaves

In three experiments measurements of photosynthesis were madeon single leaves of white clover (Trifolium repens L.) on threecultivars grown in a controlled environment. Plants which had grown under an irradiance of 30 J m^–2s^–1, or in shade within a simulated mixed sward, producedleaves with photosynthetic capacities some 30 per cent lowerthan did plants grown at 120 J m^–2 s^–1 without shade.There were no differences between treatments either in photosynthesismeasured at 30 J m^–2 s^–1, or in respiration ratesper unit leaf dry weight. Respiration per unit leaf area washigher in the plants grown at 120 J m^–2 s^–1, reflectingthe lower specific leaf area of these leaves. There were nodifferences between the three cultivars examined. Leaves which were removed from the shade of a simulated swardshortly after becoming half expanded achieved photosyntheticcapacities as high as those which were in full light throughouttheir development. It is suggested that it is this characteristicwhich enables clover plants growing in an increasingly densemixed sward to produce a succession of leaves of high photosyntheticcapacity, even though each lamina only reaches the top of thesward at a relatively late stage in its development. Trifolium repens L., white clover, photosynthesis, leaf expansion, shade, specific leaf area, stomatal conductance     

Temporal and Spatial Development of the Cells of the Expanding First Leaf of Arabidopsis thaliana (L.) Heynh

The three-dimensional quantitative leaf anatomy in developingyoung (9–22 d) first leaves of wild type Arabidopsis thalianacv. Landsberg erecta from mitosis through cell and leaf expansionto the cessation of lamina growth has been studied. The domainsof cell division, the relative proportion of the cell typespresent during development and the production of intercellularspace in the developing leaf have been determined by image analysisof entire leaves sectioned in three planes. Mitotic activityoccurs throughout the youngest leaves prior to unfolding andcell expansion is initiated firstly at the leaf tip with a persistentzone of mitotic cells at the leaf base resulting in a gradientof development along the leaf axis, which persists in the olderleaves. Major anatomical changes which occur during the developmentare, a rapid increase in mesophyll volume, an increase in thevein network, and expansion of the intercellular spaces. Thepattern of cell expansion results in a 10-fold variation inmesophyll cell size in mature leaves. In the youngest leavesthe plan area of mesophyll cells varies between 100 µm²and 400 µm² whereas in mature leaves mesophyll cells rangein plan area from 800 µm² to 9500 µm². The volumesof mesophyll tissue and airspace under unit leaf area increase3-fold and 35-fold, respectively, during leaf expansion. Thevolume proportions of tissue types mesophyll:airspace:epiderrnal:vascularin the mature leaf are 61:26:12:1, respectively. This studyprovides comparative information for future identification andanalysis of leaf development mutants of Arabidopsis thaliana. Key words: Arabidopsis, quantitative leaf anatomy, leaf expansion, image analysis     

Diurnal Extension Rates of Wheat Leaves in Relation to Temperatures and Carbohydrate Concentrations of the Extension Zone

The objective of this experiment was to determine how diurnalvariations in rates of leaf extension of wheat plants in anirrigated field crop were related to temperatures and carbohydrateconcentrations of the extension zone. Leaves 3, 4. 5 of themain shoot were studied as each emerged from the encirclingsheath. The carbohydrates in the extension zone of the emergingleaf were analysed by converting them to glucose-6-phosphateand then measuring the reduction of NADP in the presence ofglucose-6-phosphate dehydrogenase. Average hexose concentrations(glucose and fructose) increased each day from 4 up to 5 mgg^–1 fr. wt. and sucrose from 3 up to 7 mg g^–1 fr.wt. with the maximum in mid-afternoon; there were no differencesamong the three leaves. Concentrations of fructans were constantthroughout the day for leaves 3 and 4 but showed a mid-afternoonrise in leaf 5. The average concentrations of fructans in theextension zones increased from 0 to 5 to 11 mg g^–1 fr.wt. for leaves 3, 4, and 5 respectively and was consistent withthe conclusion that there was an increasing over-supply of carbohydratesfor growth of the shoot as the plant increased in size. Ratesof leaf extension were correlated with temperature but not withhexose concentrations. We concluded that the supply of carbohydratesdid not limit the growth of leaves under field conditions buttheir utilization in leaf growth was limited by temperature.The rates of leaf extension increased exponentially with temperatureand the relationship was described by the Arrhenius equation.The Q10 at 15 °C for leaf extension was 2.7 for leaves 4and 5 and 3.2 for leaf 3.     

Difference in light-induced increase in ploidy level and cell size between adaxial and abaxial epidermal pavement cells of Phaseolus vulgaris primary leaves

Changes in nuclear DNA content and cell size of adaxial andabaxial epidermal pavement cells were investigated using brightlight-induced leaf expansion of Phaseolus vulgaris plants. Inprimary leaves of bean plants grown under high (sunlight) ormoderate (ML; photon flux density, 163 µmol m^–2s^–1) light, most adaxial epidermal pavement cells hada nucleus with the 4C amount of DNA, whereas most abaxial pavementcells had a 2C nucleus. In contrast, plants grown under lowintensity white light (LL; 15 µmol m^–2 s^–1)for 13 d, when cell proliferation of epidermal pavement cellshad already finished, had a 2C nuclear DNA content in most adaxialpavement cells. When these LL-grown plants were transferredto ML, the increase in irradiance raised the frequency of 4Cnuclei in adaxial but not in abaxial pavement cells within 4d. On the other hand, the size of abaxial pavement cells increasedby 53% within 4 d of transfer to ML and remained unchanged thereafter,whereas adaxial pavement cells continuously enlarged for 12d. This suggests that the increase in adaxial cell size after4 d is supported by the nuclear DNA doubling. The differentresponses between adaxial and abaxial epidermal cells were notinduced by the different light intensity at both surfaces. Itwas shown that adaxial epidermal cells have a different propertythan abaxial ones. Key words: Cell enlargement, endopolyploidization, epidermal pavement cells, incident light intensity, leaf expansion, nuclear DNA content, Phaseolus vulgaris     

Sink Activity Estimation by Sink Size and Dry Matter Increase During the Ripening Stage of Barley (Hordeum vu/gare) and Rice (Oryza sativa)

During the ripening stage of barley and rice, the sink activitywas defined as the dry matter increase per units sink size,leaf area and time, as follows: NAR = A.SinkW+NAR', where NAR is the net assimilation rate (g d.wt dm^–2d^–1);A is the sink activity [g d.wt g^–1d.wt (ear) dm^–2d^–1]; Sink W is ear wt per plant at heading (g d.wt);and NAR' is net assimilation rate excluding the assimilate ofsink organ (g d.wt dm^–2 d^–1). Plant material with 16 combinations of mutually different sink(ear) and source (leaf) size were produced at heading for eachcrop: parts of each leaf and ear were removed to produce fourgrades in barley, and also a part of each leaf was removed producingfour grades for four rice varieties showing different ear size.NAR and NAR' were determined during 26 and 21 d in barley andrice after heading, respectively. Sink activity (A), representedas the assimilation rate induced by the sink organ, was estimatedfrom the relationship between SinkW and NAR using the previousequation. The sink activity was significantly higher in ricewith a value of 0–0.028 g d.wt g^–1 d.wt (ear) dm^–2d^–1 vs. 0–0.0017 in barley, suggesting that therelative role of leaves for grain filling is considerably higherin rice than in barley. The sink activity obtained in the studymight be introduced into a model to predict the yields of barleyand rice. Hordeum vulgare L, barley, Oryza saliva L, rice, dry matter, NAR, sink, source, sink activity, model     

Carbon Dioxide Exchange of Spring-wheat in Relation to Age and Photon-flux Density at Different Growth Temperatures

CO₂-exchange rates (CER) of the sixth and the flag leaves oftwo spring-wheat varieties, Kolibri and Famos, were comparedusing an open-circuit infrared gas analysing system. Measurementswere repeated every two weeks starting when leaf blades werefully expanded. Single plants were grown in a controlled environmenthaving a photopuiod of 15 h and a day/night temperature of 24/19°C(H), 18/13 °C (M), and 12/7 °C (L) respectively untilapprox. 2 weeks after anthesis and at 18/13 °C until maturity.The photosynthetic photon-flux density (PPFD) at the top ofthe plants was 500 µE m^–2 sec^–1. During themeasurements PPFD was gradually reduced from 2000 to 0 µEm^–2 sec^–1 whereas the temperature was maintainedat the respctive growth-temperatures during the light period.The CER of the sixth leaf declined fairly similarly for bothvarieties, except for Kolibri where a faster decline was observedduring the first two weeks after full leaf expansion. The CERof the flag leaf declined more slowly than that of the sixthleaf. With the flag leaf of Famos, the decline was nearly linear,whereas with Kolibri it was very slow during the first few weeksbut rapid as the leaves further senesced. This pattern becamemore pronounced as the growth temperature decreased. The declinein relation to leaf age was much smaller at low PPFD than athigh PPFD during the same period. At full leaf expansion Kolibrireached higher maximum CER than Famos except at H. As the PPFDwas reduced the difference became smaller and at very low PPFDsuch as 50 µE m^–2 sec^–1 was reversed for thesixth leaf. Under optimum growth conditions maximum values ofCER were greater than 50mg CO₂ dm^–2h^–1 and PPFDfor light saturation was close to 2000 µE m^–2 sec^–1.A comparison between the actual CER and a fitted curve widelyused, PN=(a+b/l)^–1–DR, showed that the goodnessof fit strongly depends on cultivar, treatment and leaf ageas well as on the number and the level of PPFD from which datafor calculations are taken. Triticum aestivum, L., wheat, photosynthesis, photon-flux density, light response, carbon, dioxide exchange     

Effects of Temperature on Growth and Nitrogen Fixation by Swards of Subterranean Clover

Subterranean clover (Trifolium subterraneum L.) cv. ‘Woogenellup’ swards were grown at 10, 15, 20 and 25 Cwith a 12 h photoperiod of 500 or 1000 µmol m^–2s^–1 [low and high photosynthetic photon flux density (PPFD)].Nitrogen-fixing swards received nutrient solution lacking combinednitrogen while control swards received a complete nutrient solution.Growth was measured by infra-red analysis of carbon dioxideexchange and by accumulation of dry matter. Swards were harvestedat intervals between 95 and 570 g d. wt m^–2 for estimationof nitrogenase activity by acetylene reduction and hydrogenevolution assays. Nitrogen fixation was also measured by increasein organic nitrogen. The growth rate was highest at 10 C at low PPFD, and at 10–15C at high PPFD. Nitrogen-fixing swards grew slower than thosereceiving combined nitrogen. Nitrogen fixation measured by increasein organic nitrogen responded similarly to the growth rate,as did acetylene reduction between 10 and 20 C. At 25 C therelationship between acetylene reduction and nitrogen fixationwas distrupted. The difference between the rates of acetylenereduction and hydrogen evolution, theoretically proportionalto nitrogen fixation, was not a reliable indicator of nitrogenfixation because hydrogen uptake developed. Trifolium subterraneum L, subterranean clover, growth, nitrogen fixation, temperature, acetylene reduction     

The Growth Rate of Wheat Leaves in Relation to the Extension Zone Sugar Concentration Manipulated by Shading

The main objective of this study was to determine the relationshipbetween the relative rate of growth of emerging wheat leavesand the hexose sugar concentration of the extension zone. Shortperiods of intense shading (to 20 or 5% of full sun for up to14 d) were used to decrease hexose concentrations. Shading decreased hexose concentrations to a fraction of thatof controls and also resulted in thin and narrow leaves thatwere less in dry weight than control leaves of the same length.Shading did however increase the length of the zone of extendingtissue at the leaf base by 30%. The effect of hexose concentrations on the relative rate ofleaf growth was evaluated by determining the ratio between growthrates of shaded and control leaves. This ratio declined as hexoseconcentrations declined and the relationship was described bya rectangular hyperbola (r > 0.95, P < 0.01). Combineddata from many leaves on the main shoot and its tillers fromtwo irrigated wheat crops all conformed to the same relationship.The hexose concentrations where the ratio of growth rates washalf the maximum rate were 0.42 mg g^–1 fr. wt. for extensiongrowth and 1.74 mg g^–1 fr. wt. for dry weight growth.These values were significantly (P < 0.01) different. These results were compared with data from emerging leaves offield crops and it was concluded that hexose concentrationshad not limited leaf growth rates, the lowest values recordedbeing 2.5–3.0 mg g^–1 fr. wt. It was further suggestedas unlikely that leaf growth rates of wheat crops in the fieldwould be limited by hexose concentrations.     

The Effects of CO2 Enrichment and Nutrient Supply on Growth Morphology and Anatomy of Phaseolus vulgaris L. Seedlings

Plants of Phaseolus vulgaris were grown from seed in open-topgrowth chambers at the present (P, 350 µmol mol^–1)atmospheric CO₂ concentration and at an elevated (E, 700 µmolmol^–1) CO₂ concentration, and at low (L, without additionalnutrient solution) and high (H, with additional nutrient solution)nutrient supply for 28 d The effects of CO₂ and nutrient availabilitywere examined on growth, morphological and biochemical characteristics Leaf area and dry mass were significantly increased by CO₂ enrichmentand by high nutrient supply Stomatal density, stomatal indexand epidermal cell density were not affected by elevated CO₂concentration or by nutrient supply Leaf thickness respondedpositively to CO₂ increasing particularly in mesophyll areaas a result of cell enlargement Intercellular air spaces inthe mesophyll decreased slightly in plants grown in elevatedCO₂ Leaf chlorophyll content per unit area or dry mass was significantlylower in elevated CO₂ grown plants and increased significantlywith increasing nutrient availability The content of reducingcarbohydrates of leaves, stem, and roots was not affected byCO₂ but was significantly increased by nutrient addition inall plant parts Starch content in leaves and stem was significantlyincreased by elevated CO₂ concentration and by high nutrientsupply Phaseolus vulgaris, elevated atmospheric CO₂, CO₂-nutrient interaction, stomatal density, leaf anatomy, chlorophyll, carbohydrates, starch     

Afternoon Depression In Photosynthesis in Grapevine Leaves--Evidence for a High Light Stress Effect

A midday depression in net photosynthesis and in stomatal conductancewas observed when leaves of well-watered Vitis vinifera plantswere subjected to a diurnal pattern of variation in leaf temperatureand leaf-to-air water vapour pressure difference similar toa summer day, while photon flux density was kept constant at1450 µmolm^–2 s^–1,. When leaves were kept atconstant leaf temperature (22.5°C) and leaf-to-air watervapour presure difference (8.5 Pa kPa^–1) at the same lightintensity, stomata opened with the onset of illumination andmaximal conductance and photosynthesis values were observedabout 1 h later. Subsequently, conductance and photosynthesisdecreased gradually. Leaf water potential never dropped below{macron}0.3 MPa. Leaves kept under constant environmental conditionsshowed an afternoon decline in photosynthesis at high internalCO₂, in carboxylation efficiency and in maximum conductanceas well as an increase in stomatal sensitivity to CO₂. Whenthe photon flux density during the day was reduced to 750 µmolm^–2 s^–1, the afternoon depression in gas exchangerates was attenuated. To evaluate the possible effects of highlight stress on changes in chloroplastic behaviour we comparedlight response curves of photosynthesis determined with an oxygenelectrode, in the morning and in the afternoon after the plantswere exposed to either high or moderate photon flux densities.A significant depression in photosynthetic capacity was foundby this method in high light treated leaves, but not in leavespreviously exposed to moderate photon flux density. Apparentquantum yield decreased in the afternoon, particularly afterexposure to high light. Maximum chlorophyll a fluorescence at22°C was reduced and the quenching of fluorescence afterreaching the peak was slower in the afternoon than in the morning,especially in high light-treated leaves. Changes in the patternsof chlorophyll fluorescence kinetics were observed after lighttreatment, i.e. in the afternoon, with oscillations either absent(after high light) or significantly reduced (after moderatelight) in comparison to the morning. The significance of theseresults is discussed and it is suggested that a direct inhibitoryeffect of high light at the chloroplast level provides the bestinterpretation for the observed afternoon decline in photosyntheticrate. Key words: Carboxylation efficiency, chlorophyll fluorescence, photosynthetic capacity, quantum yield, stomatal conductance, Vitis vinifera L.