Further Effects of Light Intensity, Carbon Dioxide Concentration, and Day Temperature on the Growth of Chrysanthemum morifolium cv. Bright Golden Anne in Controlled Environments

In earlier work the effects of light intensity over the range31 to 250 J cm^–2 day^–1 and carbon dioxide concentrationfrom 325 to 900 ppm with 8-h days at 18.3 °C and 16-h nightsat 15.6 °C were described. The present paper is concernedwith three further experiments with light levels up to 375 Jcm^–2 day^–1 (which corresponds to the daily totalin a glasshouse in southern England in early May or August andthe intensity is approximately that of mid-winter sunshine),carbon dioxide concentration up to 1500 ppm, and day temperaturesof 18.3 to 29.4 °C. Final plant weight was increased by light over the range 125–375J cm^–2 day^–1 and by carbon dioxide over the range325–900 ppm, with positive interaction between them; thisinteraction was increased by raising the temperature to 23.9°C and somewhat more at 29.4 °C day temperature. Leaf-arearatio and specific leaf area were reduced by increasing eitherlight or carbon dioxide but there was little effect of temperature.Leaf-weight ratios were uniform within experiments but therewere small consistent differences between one experiment andthe other two which also affected leaf-area ratios. Mean unit leaf rate was scarcely affected by day temperatureover the range investigated. There were the usual increasesdue to increased light and carbon dioxide concentration anda consistent difference in absolute value between one experimentand the other two. These differences in mean unit leaf rateare illustrated in detail in the ontogenetic trend of unit leafrate and plant size. Lower unit leaf rates were to a considerableextent compensated for by increased leaf-area ratios in theusual way. Despite the substantial differences in day temperature the specificwater contents (g water g dry weight^–1) differed little,showing in the majority of cases higher values in the highertemperature for otherwise similar treatment combinations. Flower development was somewhat delayed at 23.9 °C day temperature,and substantially so at 29.4 °C. Lateral branch length wasincreased at 23.9 °C and excessively so at 29.4 °C.This reveals quite clearly that a temperature optimum for vegetativegrowth may not be the optimum for flowering performance norproduce a desirable plant shape. Despite the marked effects of temperature on rate of flowerdevelopment, the relationship between flower development andthe ratio of flower to total weight was the same for all treatmentcombinations in all three experiments and coincident with thatreported earlier. Gasometric determinations indicated that respiratory loss bythe whole plant was a smaller proportion of net photosyntheticgain at a temperature of 29.4 °C than at 18.3 °C andwas likewise a smaller proportion at 1500 ppm carbon dioxidethan at 325 ppm. If photorespiration of leaves is assumed tobe as great as their dark respiration, the respiratory lossesare in the range of 31–50 per cent of the gross gain.Greater rates of photorespiration would increase the proportionaterespiratory loss.     

The Effects of Light Intensity and Carbon Dioxide Concentration on the Growth of Chrysanthemum morifolium cv. Bright Golden Anne

Rooted cuttings were grown in controlled-environment cabinetsat daily visible light totals of 31, 63, 125, and 250 J cm^–28-h day^–1 and carbon dioxide concentrations of 325 and600 ppm. The experiment was repeated on another occasion withthe inclusion of a further carbon dioxide level of 900 ppm.A 5-h tungsten night break was used in the first week to delayflower initiation The plants in the various treatment combinationswere sampled by frequent small harvests for leaf area and freshand dry weights of leaf, stem, root, and flower, and also forvarious morphological features. Other growth measures were obtainedby manipulation of the primary data, including the fitting ofprogress curves. Plants were respaced at intervals to minimizemutual shading. There was an increase in total dry-matter production with increasinglight and carbon dioxide, with a small positive interactionbetween them. Plants in one experiment had a somewhat higherunit leaf rate and a lower leaf-area ratio, the latter beingdue to a slightly smaller leaf-weight ratio. The effects ofadditional carbon dioxide were largely accounted for by increasedphotosynthesis. Although there were substantial differencesin specific leaf area between treatment combinations withineach experiment, the leaf-weight ratio was little altered inthe period of vegetative growth. The inverse relationship betweenspecific leaf area and unit leaf rate showed a very similartrend for all combinations of light and carbon dioxide concentration.Leaf area was a linear function of absolute leaf water contentfor all treatment combinations within an experiment, but therewas a small significant difference between occasions. Flower development was extremely delayed in the lowest lightlevel and substantially delayed at the next higher level. Thenumber of leaves below the flower decreased with increasinglight level Flower weight increased with increasing light above63 J cm^–2 8-h day^–1 and with increasing carbon dioxideconcentration, there being a positive interaction between them The initial weight and leaf area of cuttings differed for thetwo experiments, and although the results on the two occasionswere in the same direction, their magnitudes were different.Some of the discrepancy was eliminated by expressing the variousgrowth measures as functions of plant dry weight, but therewas evidently a difference in the potential for growth of thetwo batches of cuttings. The plants which were initially smallerhad a higher average unit leaf rate which, due to a higher leafwater content, was not offset by a lower leaf area ratio.     

Development and Control of the Number of Flowers per Node in Pisum sativum L.

Non-dormant flower initials are laid down in the axils of successiveleaf initials as they are formed by the apical meristem of Pisumsativum L. In cultivars with a maximum capability of two flowersper raceme, the undeveloped flower meristem divides into twoportions. One forms the first flower and the other either developsinto a small protrusion on one side of the first flower or becomesthe second flower, depending on the prevailing environment.Flower development in conditions favouring single-flowered racemeswas advanced by one plastochron. Variation in the number offlowers per raceme occurs between cultivars and between environments.The number of double flowers formed was favoured by higher lightintensity (120 Js^–1 m^–2) and carbon dioxide concentration(330 µ11^–) and lower temperature (15°C). Incultivars producing more than two flowers per raceme, lowerlight intensity (60 Js^–1 m^–2) plus higher temperature(20°C) increased the mean number of flowers per raceme.Soluble sugar levels in all varieties were higher (36.05 mgeq glucose g^–1 fresh weight) in the low temperature/highlight environment than the high temperature/low light environment(14.80 mg eq glucose g^–1 fresh weight). The flowering potential and stability of 13 cultivars have beenassessed in controlled environment and in sowing date trialsin the field. A stable variety, which consistently producedtwo flowers per raceme, was identified in controlled environmentand its stability was maintained in field trials. A linear regressionof stability of flower number in the field on stability in controlledenvironment accounted for 89.6 per cent of the variance (P<5per cent), but the flowering potential in a sowing date experimentwas not related to temperature or radiation intensity.     

The Variation in Response to Light Intensity and Carbon Dioxide Concentration Shown by Two Cultivars of Chrysanthemum morifolium Grown in Controlled Environments at Two Times of Year

The growth of the cultivar Golden Princess Anne (G.P.A.) wasstudied in controlled announcement cabinets in a range of lightconditions (125–375 J cm^–2 8-h day^–1) andcarbon dioxide concentrations (325–1500 ppm) in all combinationsPlants obtained in January and grown from January to April showedgreater final total dry weight and flower dry weight at bothhigher light intensity and higher carbon dioxide concentrationwith a strong positive interaction between them, whereas plantsobtained in September and grown from September to December didnot respond much to increased carbon dioxide concentration andthere was only a small positive interaction with light intensity.The plants grown from January to April had larger final leafareas, larger mean leaf-area ratios due mainly to larger specificleaf areas, and higher mean specific leaf-water contents comparedwith September–December plants. Despite the differencein specific leaf-water content, leaf area was almost the samelinear function of absolute leaf-water content at both timesof year. The other vegetative parts also had higher specificwater contents throughout the January–April experimentand the lateral branches were longer when compared with thecorresponding values for September–December Flower developmentwas slightly faster in September–December and the plantsbore on average one flowering branch less compared with January–Aprilplants. Plants in the lower light and carbon dioxide conditions hadlower unit leaf rates, but for plants of similar total dry weightthe effects of this on dry-matter increment were partially offsetby larger leaf areas at both times of year. The January–Aprilplants had greater leaf areas than September–Decemberplants of similar unit leaf rate and total dry weight. The cultivar Bright Golden Anne (B.G.A ) showed effects whichwere in the same direction but smaller in magnitude, tendingto diminish the differences between the times of year For example,the positive interaction in total plant dry weight was smallerin January–April compared with G P A , but larger in September–December.Leaf area, leaf-area ratio, specific leaf area, specific watercontent of leaf, stem, and root, and lateral branch length,were all larger for B G A in corresponding treatment-combinationsin two January–April experiments than in a September–Decemberone, although the difference between the times of year was smallerthan for G.P.A except for leaf area which was relatively butnot absolutely smaller Dry-matter increment and leaf area showedan inverse relationship for plants of the same total dry weight,as in G P A. In January–April B G.A plants of similarunit leaf rate and total dry weight also had greater leaf areasthan in September–December but the differences were notso large as for G.P.A Total dry-matter production was slightlygreater for B.G.A. in January–April and considerably greaterin September–December compared with G P A , and at bothtimes of year B.G.A. was more leafy, with higher specific watercontents for the vegetative parts. It was not possible to determine the cause of the differencesin growth obtained at the two times of year. It could have arisenbefore the cuttings were removed from the stock plants, duringpropagation, or during the course of the experiments in thegrowth cabinets.     

Mutual Shading in Quantitative Studies

For interpreting growth studies it is necessary to know to whatextent, if any, the experimental plants are interfering witheach other, especially by shading. It is also desirable to useexpensive experimental space as efficiently as possible. Plantsshould be spaced only as widely as needed to reduce mutual shadingto a negligible level, and hence a means of estimating the interferencebetween plants is required. The situation is assessed in thecase of Callistephus chinensis in growth cabinets by consideringthe efficiency of energy conversion on a unit leaf-area basisin relation to the leaf-index of the cabinet, bearing in mindthat the latter is changing due to the continuous growth ofthe plants, on the one hand, and the removal of plants for harvestat discrete intervals, on the other. In the example illustratedit was demonstrated that mutual shading caused a depressionof less than 10 per cent in growth of the individual plantson about 25 days during the total experimental period of 126days in the case of the treatments with 325 and 600 ppm carbondioxide and less than 5 per cent in the 900 ppm treatment. Itis suggested that a depression of 5 per cent be regarded asthe criterion of mutual shading, and it is explained how theleaf-area index in such conditions corresponds to the self-shadingfactor of the plant for the light source concerned.     

Effects of Different CO2 Environments on the Photosynthesis-Yield Relationship and the Carbon and Water Balance of a White Clover (Trifolium repens L. cv. Blanca) Sward

Effects of atmospheric CO₂ enrichment to a level above 600 parts10^–6 on leaf and canopy gas exchange characteristics wereinvestigated in Trifolium repens, using an open system for gasexchange measurement. The cuvettes of the system served as growthchambers, allowing continuous measurement in a semi-controlledenvironment of ±350 and ±600 parts 10^–6CO₂, respectively. Carbon balance data were compared with cropyield and effects on the canopy level were compared with measuredleaf responses of photosynthesis and stomatal behaviour. Photosyntheticstimulation by high CO₂ was stronger at the canopy level (103%on average) than for leaves (90% in full light), as a consequenceof accelerated foliage area development. The latter increasedabsolute water consumption by 16%, despite strong stomatal closure.The overall result was a 63% improvement in canopy water useefficiency (WUE), while leaf WVE increased almost 3-fold insaturating light. The stomatal response was such that, whilethe internal CO₂ concentration in the leaf, ch increased withrising atmospherical CO₂ concentration, c_a, ci/c_a was somewhatdecreased. Total canopy resistance, R_c, was generally lowerat high CO₂ levels, despite higher leaf resistance. Higher canopyCO₂ loss at night and faster light extinction in a larger-sizedhigh CO₂ canopy were major drawbacks which prevented a furtherincrease in dry matter production (the harvest index was increasedby a factor 1.83). Key words: CO₂ enrichment, canopy CO₂ exchange, carbon balance, water use efficiency, leaf and canopy resistance     

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     

Effect of CO2 Concentration on Growth of Sugar-beet, Barley, Kale, and Maize

Increasing the concentration of CO₂ in the air from the usual300 ppm to 1, 000 ppm in growth rooms with temperatures of 20°C during the 16-h light period and 15° C during the 8-hdark period increased the total dry weight of sugar-beet, barley,and kale by about 5o per cent. A further increase in CO, concentrationto 3, 300 ppm increased dry weight slightly more. These effectsoccurred with light intensities ranging from 3.7 to II.6 caldm–² min–¹ of visible radiation supplied by a mixtureof fluorescent and tungsten lamps, and were only slightly greaterwith the brighter light. Extra CO₂ also increased leaf area,though relatively less than dry weight, and the number of barleyshoots but not of sugar-beet or kale leaves; it decreased leaf-arearatio, specific leaf area, and the ratio of tops to roots. Maizewas taller with extra CO₂. Net assimilation rates in 1, 000 and 3, 300 ppm CO₂ were about20 and 30 per cent respectively greater than in 300 ppm. Uptakeof CO₂ in the light by complete tops and single leaves alsoincreased with increase in CO₂ concentration. Photosynthesisof leaves of plants recently transferred to a new CO₂ concentrationdepended only on that concentration and not on the originalone. Doubling the light intensity from 3.7 to 7.7 cal dm–²min–¹ affected dry weight, leaf area, net assimilationrate, etc., similarly to a tenfold increase in CO₂ concentration.     

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     

Kinetics of Leaf Growth in Lolium temulentum at Optimal and Chilling Temperatures

Lolium temulentum plants were grown at 20 °C, under an 8-hdaylength, in a controlled-environment chamber, and the kineticsof leaf expansion were observed by measuring the movement ofan optical grid attached to the fourth leaf. The leaf emerged23–24 d after sowing and was fully expanded 9–10d later. Extension rate was maximal between the second and fifthdays after emergence and declined markedly thereafter. Duringthe rapid growth phase the rate of elongation exhibited a distinctdiurnal rhythm, fluctuating between 1.9 to 2.3 mm h^–1in the light period, and 1.3 to 1.7 mm h^–1 in the dark.A circadian oscillation with a period of about 27 h was observedin leaves elongating in continuous darkness. When plants weretransferred to 5 °C soon after emergence of the fourth leafthere was an immediate reduction in rate of growth to about22 per cent of the rate at 20 °C: the Q₁₀ for the mean elongationrate in the range 20–5 °C was 3.7. When plants weretransferred from 20 to 2 °C at fourth leaf emergence, meanextension rate declined to less than 5 per cent, correspondingto a Q₁₀ in the range 5–2 °C of more than 300. Furthermore,growth at 2 °C was confined almost entirely to the darkphase of the photoperiod cycle. The responsive tissue was shownto be a small area of expanding leafless than 1.5 cm above theshoot apex and the possible mechanisms underlying low temperatureeffects in this region are discussed. Lolium temulentum L., leaf growth, auxanometer, low temperature, diurnal rhythm     

Maintenance and Growth Components of Carbon Dioxide Efflux from Growing Pea Fruits

Carbon dioxide efflux from 5- to 20-day-old pea fruits was measuredfor plants grown in controlled environment at 15 °C and600 µmol s^–1 m^–2 photon flux density in a16 h photoperiod. The rate of CO₂ output per fruit increasedquickly from 0.005 to 0.018 mg CO₂ min^–1 during fruitelongation and subsequently more slowly to 0.030 mg CO₂ min^–1as the fruits inflated. On a d. wt basis the rate was highest,0.175 mg CO₂ g^–1 min^–1, in the youngest fruits anddeclined curvilinearly with increasing fruit weight to 0.02mg CO₂ g^–1 min^–1. Separation of maintenance andgrowth components was achieved by starvation methods and bymultiple regression analysis. From the latter method estimatesof the maintenance coefficient declined hyperbolically from150±8.7 mg carbohydrate g^–1 d. wt day^–1 inthe very young fruits (0.05 g) to 10.4±0.36 mg carbohydrateg^–1 d. wt day^–1 in older fruits (2.0 g). On a nitrogenbasis maintenance costs decreased from 2240 to 310 mg carbohydrateg^–1 nitrogen day^–1 while nitrogen concentrationfell from 6.7 to 3 per cent d. wt. A simple linear relationshipbetween maintenance cost per unit d. wt and nitrogen concentrationwas not observed. A growth coefficient of 50±6.7 mg carbohydrate g^–1growth (equivalent to a conversion efficiency, Y_G, of 0.95)was estimated for all fruits examined. The overall efficiency, Y, increased from a mean of 0.70 to0.85 during fruit elongation and subsequently declined to 0.80.For a given fruit weight, efficiency increased asymptoticallywith relative growth rate; both asymptote and slope of the relationshipincreased as the fruits grew. Pisum sativum L., garden pea, legume fruit, carbon dioxide efflux, maintenance respiration, growth respiration     

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.     

The Effect of Current Photosynthesis on the Origin of Translocates in Old Tomato Leaves

The rate of carbon transport from an old tomato leaf (54 days),grown at 80 W m^–2, was measured under light flux densitiesbetween 7 and 90 W m^–2. Under low light, the rate of carbontransport over a 6 h period was about 1 mg C dm^–2 h^–1,well in excess of the concurrent photosynthetic rate. The lossfrom these leaves of ¹⁴C-leaf assimilate which was fixed beforethe experimental period amounted to 62 per cent of the totalinitial uptake and was higher than that from leaves with higherconcurrent photosynthetic rates. The higher loss of ¹⁴C fromleaves with low photosynthetic rates was due to a greater contributionof ¹⁴C from the starch and residue fractions. The rate of transportappeared to be determined by the concentration of the labilesucrose, not the total sucrose concentration. In comparisonwith young fully-expanded tomato leaves (Ho, 1976) the sizeof the labile sucrose pool appeared to decrease with age. Thephotosynthesistranslocation coefficient was low (k₁k₂=0•21)for an old tomato leaf. Based on these results a scheme of carbonpartitioning in relation to translocation is proposed. Criteriafor assessing the efficiency of translocation in leaves arediscussed.     

Nitrogen Fixation in the Phyllosphere of Tropical Plants: Occurrence of Phyllosphere Nitrogen-Fixing Micro-organisms in Eastern India and their Utility for the Growth and Nitrogen Nutrition of Host Plants

Of the 560 leaf samples belonging to 259 species of green plantsexamined more than 50 per cent of the Angiosperms and 25 percent of the Pteridophytes and Gymnosperms revealed the presenceof N₂-fixing micro-organisms in their phyllosphere. Plants particularlyremarkable in this respect are orchids and several other epiphytes,Scindapsus officinalis, Ficus and cucurbits. Most of the isolatesappear to be biotypes of Klebsiella pneumoniae. The more activestrains fixed more than 5 mg N g^–1 glucose utilized andreduced more than 100 nmol C₂H₂ mg^–1 cell d. w h^–1. The efficacy of the phyllosphere N₂-fixing isolates for N-nutritionof host plants was studied by spraying suspensions of the culturesgrown on N-free media on rice and wheat seedlings. In IR-26rice or Sonalika and Janak wheat grown on soil in wooden flatsor earthenware pots, 22 per cent of the 161 cultures studiedcaused increased height and about three-quarters of the culturesenhanced dry weight by more than 50 per cent; chlorophyll andN-contents were enhanced more than 50 per cent by about halfand two-thirds of the cultures respectively. In N-free sandculture 26 of the 50 promising strains doubled N-content, and30 doubled dry weight of the tested plants. In some cases dryweight, number of grains per panicle, and 1000 grain weightwere increased by 300, 70–83 and 126–158 per centrespectively; N-content of straw and seed was increased three-or fourfold. In several cases the beneficial effects were foundto match closely the performance of plants receiving ammoniumsulphate. Nitrogen-fixing micro-organisms, nitrogen nutrition, phyllosphere, rice, tropical plants, wheat     

Light Distribution and Photosynthesis in Field Crops

In a new model of light distribution in field crops a parameters is the fraction of light passing through unit leaf layer withoutinterception. Radiation profiles measured with solarimetersand photocells give values of s from 0.7 for grasses to 0.4for species with prostrate leaves. Knowing s, leaf transmissionT and leaf-area index L the light distribution in a field cropmay be described by a binomial expansion of the form {s+(I-s)T)^L.To calculate crop photosynthesis at given light intensity thisexpansion is combined with two parameters describing the shapeof the light-response curve of single leaves. Finally, the assumptionthat solar radiation varies sinusoidally allows daily totalphotosynthesis to be estimated from daylength and insolation. The theory predicts about the same potential photosynthesisin a cloudy temperte climate with long days as in a more sunnyequatorial climate with short days. When L < 3 photosynthesisincreases as s decreases, i.e. as leaves become more prostrate;but when L > 5, photosynthesis increases as s increases,i. e. as leaves become more erect. Assuming that respirationis proportional to leaf area, estimated dry-matter productionagrees well with field measurements on sugar-beet, sugar-cane,kale, and subterranean clover. Estimates of maximum gross photosynthesis(for sugar-cane and maize) range from 60 to 9 g m^–2 day^–1depending on insolation.     

An Analysis of the Growth of Young Tomato Plants in Water Culture at Different Light Integrals and CO2 Concentrations: I. Physiological Aspects

Young tomato plants were grown from germination in water cultureat light-flux densities from 6 to 110 W m^-2 (400–700 nm),daylengths from 8 to 24 h and CO₂ concentrations from 0.4 to2.2 g CO² m^-3 in controlled environment cabinets. The growth rates and net assimilation rates of 14–17-day-oldplants at the highest light integrals were appreciably greaterthan most values previously recorded for tomato, and diminishedwith time. Plants in the lowest light conditions had leaf arearatios five times larger than those in the highest light, attributablemainly to a difference in leaf dry weight/area. Such flexibilityin leaf area ratio has not previously been associated with ‘sun’plants such as the tomato. Relatively normal growth was obtained in continuous light, incontrast to most other reports. This may have been due to theuse of conditions which would minimise water stress. The efficiency of the conversion of incident light energy tochemical energy by the whole plant ranged from 15 per cent inseedlings in low continuous light to about 6 per cent, tendingto be higher in young plants in long days under CO₂ enrichment.The higher values are probably overestimates because of theexclusion of reflected light from the energy receipt values.     

Physiological and Ecological Studies in the Analysis of Plant Environment: XII. The Role of the Light Factor in Limiting Growth

Previous investigations in southern England on twenty-two herbaceousspecies have demonstrated that for widely spaced plants thediurnal solar radiation limits the net assimilation rate ofall species and restricts the relative growth rate of many.In examining how far these limitations apply to other environmentsit is now shown that in the subtropics and tropics the levelsof net assimilation rate and relative growth rate can greatlyexceed those so far recorded for cool temperate regions, andthese differences are attributed to the higher insolation andtemperatures. From a variety of evidence it is concluded that as the distancebetween plants is reduced 8O the net assimilation rate is progressivelydiminished even in regions of high insolation through the enhancedmutual shading. In consequence levels of light which may besupra-optimal for relatively isolated individuals may yet limitthe dry-matter production of a dense population. There is anoptimal ratio of leaf area to ground surface (leaf-area index)for the maximal exploitation of the incoming radiation in carbonfixation by the population and this optimum will vary with thespecies and the light intensity. Where other environmental factorsare favourable, light may limit dry-matter production everywhere. On an annual basis dry-matter production will be dependent ontwo components—the length of the ‘growing season’and the period over which the leaf-area index remains optimal.In the tropics the highest annual rate of production so farrecorded is 7⁸ tonnes/hect. produced by Saccharum officinarumandin north-east Europe 23.5 tonnes by Fagus sylvatica. Over shortperiods the rate of dry-matter production can attain 3⁸g./m.²/dayand the utilization of solar energy can be as high as 4.2 percent., or 9.5 per cent, for the range 4, 000–7, 000 A. Although information on the productivity of natural communitiesis still ex-ceedingly scanty, an attempt has been made to interpretthe general pattern in terms of the length of the growing season,the level of solar radiation, the magni-tude of the leaf-areaindex of the whole community, and the period over which theleaf canopy remains green. It is postulated that in any regionthe vegetation reaches a dynamic equilibrium when there is themaximum exploitation of the incoming radiation to produce thegreatest production of dry matter.     

Assimilation of 14CO2 by the Inflorescence of Poa annua L. and Lolium perenne L.

The relative assimilatory activity of the inflorescence, itsindividual components, and the leaves of flowering tillers ofPoa annua L. and Lolium perenneL. was determined over the periodfrom inflorescence emergence to seed shedding. The pattern of¹⁴CO₂ fixation was similar for both species and the inflorescencewas by far the most important assimilatory organ of the reproductivetiller, particularly over the latter period of seed developmentas leaf senescence progressed. With the exception of the seedsall parts of the inflorescence showed significant assimilatoryactivity and the lemmas and paleas accounted for 40–50per cent of the total ¹⁴C fixed by the inflorescence in bothspecies. The importance of the grass inflorescence as a photosyntheticstructure is discussed in relation to similar studies on cereals. Poa annua, Lolium perenne, carbon dioxide assimilation, inflorescence     

The Influence of Applied Nitrogen on Export and Partitioning of Current Assimilate by Field-grown Potato Plants

Field-grown potatoes were subjected to N deficiency (no appliedN) or received high levels of N (240 kg N ha^–1) at planting.The effects of these treatments were monitored at five stagesduring growth in terms of the allocation of photosynthate withinthe leaf, and the export and partitioning of carbon to differentsinks. N deficiency significantly raised the starch concentrationin all organs of the plants, particularly in leaves and stems,and as a consequence the total amount of starch in the canopyof the low N plants remained greater than that of the high Nplants until approx. 100 days after planting (DAP). The totalamounts of carbohydrates, protein and amino acids were calculatedfor each treatment and these values were used to derive a balancesheet for major reserves. Net losses of reserves occurred fromthe canopy in both treatments in the period 97–133 DAP,although these were shown to represent < 3 per cent of thetotal gain in tuber dry weight for the season. Partitioning of ¹⁴C assimilates was examined in whole plantsand also in single leaves. Reduced partitioning to the tubers,seen in high N plants throughout their growth, was shown tobe due to decreased percentage export by the leaf and accumulationof exported ¹⁴C by the stems. Partitioning to the tubers inlow N plants increased prior to senescence when 87 per centof the fixed ¹⁴C was exported within 24 h, 80 per cent of thisto the tubers. The equivalent values for the high N plants were77 and 60 per cent respectively. Increased percentage exportcoincided with decreased allocation to starch in the leaf, anda link between these processes is suggested. N also significantlyaltered the allocation of ¹⁴C within the leaf and may have influencedthe degradation of starch in the dark to a greater degree thanits synthesis in the light. The enzymes sucrose phosphate synthase (SPS), and starch synthasewere measured concurrently with partitioning. High N plantsshowed higher rates of activities of each of the enzymes althoughboth enzymes showed a similar pattern of development over theseason, irrespective of N treatment. The data are discussed in the light of conflicting reports concerningthe influence of N on translocation and partitioning. ¹⁴C assimilates, carbohydrates, nitrogen, potato (Solanum tuberosum L.), protein     

Short-term Products of 14C-acetate Assimilation by Chlorella pyrenoidosa in the Light

The kinetics of ¹⁴C-2-acetate assimilation by Chlorella pyrenoidosain the light were examined. Under aerobic conditions the primaryproduct of acetate assimilation was succinic acid which, afterten seconds, contained over 60 per cent of the ¹⁴C incorporatedby the cells. The percentage of the total ¹⁴C in succinate fellwith time, while that in citrate and glutamate increased. After1800 sec over 60 per cent of ¹⁴C was present in two compounds,glutamic acid and an unknown compound (X). Glucose-6-phosphate,fructose-6-phosphate, phosphoglyceric acid and phosphoenolpyruvicacid became labelled after 60 sec but together never containedmore than one per cent of the total ¹⁴C incorporated. Underanaerobic conditions succinate was still the primary productof acetate assimilation, and the absence of carbon dioxide resultedin a decrease in ¹⁴C incorporation into compound X. The patternof acetate assimilation in acetate grown and acetate adaptedChlorella was very similar to that in photo-autotrophicallygrown Chlorella. In the presence of 10^–6M DCMU, succinicacid was the primary product of acetate assimilation, but therewas an early Incorporation of ¹⁴C into glutamate, aspartate,and malate. 4 x10^–3M MFA did not effect the early incorporationof ¹⁴C into succinic acid, but resulted in accumulation of ¹⁴Cin citrate and a decreased amount in glutamate and in compound X.