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.     

Growth Analysis of Sweet Pepper (Capsicum annuum L.): 2. Interacting Effects of Irradiance, Temperature and Plant Age in Controlled Conditions

A growth analysis was carried out with sweet pepper plants grownin a phytotron. Irradiance conditions were: 0.84 or 3.25 MJm^–2 in 8 h, 1.67 MJ m^–2 in 16 h and 2.51 MJ m^–2in 24 h. Temperatures applied were 25 or 21 °C during thephotoperiod in combination with 25, 21 and 17 or 21, 17 and13 °C respectively during the nyctoperiod. Highest values for leaf area and total dry weight were foundwhen applying 1.67 MJ m^–2 in 16 h, followed by 3.25 MJm^–2 in 8 h, irrespective of the temperature regime. Continuousirradiance ultimately resulted in leaf drop. A reduction inthe day temperature decreased leaf area and total dry weight.At a day temperature of 25 °C the dry weight increased withdecreasing night temperature when applying 3.25 MJ m^–2in 8 h. At a day temperature of 21 °C leaf area and dryweight were reduced when 17 or 13 °C were applied duringa 16 h nyctoperiod. Values for relative growth rate, net assimilation rate, leafarea ratio and leaf weight ratio strongly decreased with advancingplant age. The effects of irradiance treatment on RGR and NARwere analogous to those on total dry weight while the reversepattern was observed for the LAR. A decrease in day temperaturedecreased the RGR. The effects of night temperature exhibitedstrong interactions with day temperature and photoperiod. Theinfluence of temperature on RGR was largely mediated throughchanges in the LAR. The latter parameter was highly correlatedwith the specific leaf weight. Capsicum annuum L., sweet pepper, growth analysis, irradiance, temperature, plant age     

Growth Responses of Tomato Plants in Non-aerated Water Culture to Foliar Sprays of Gibberellic Acid and Benzyladenine

Tomato plants were grown to the five-six leaf stage in aeratedwater culture and aeration then discontinued. Foliar spraysof gibberellic acid (G), N⁶ benzyladenine (B), and ammoniumnitrate (N) were applied for periods up to 7 days and the plantsharvested on the eighth day. A mixture of 2·5 ppm G,5·0 ppm B, and 280 ppm N increased growth of the wholeplant and this was attributable almost entirely to G and B.In the leaf, both increased water content (B>G) and dry weight.G, but not B, increased leaf area; B, but not G, increased freshweight leaf/unit area. In the stem, G increased dry weight andheight; B reduced height but increased diameter and water content.Inclusion of O·I ppm indol-3yl-acetic acid in the mixturewas ineffective. The percentage increase in growth of non-aerated plants withG+B+N was greater with non-acrated than with aerated plantsfor weight of whole plant and leaf area, but not for stem height.Growth of non-aerated plants could not be increased by increasingthe volume of the nutrient solution, by ‘aerating’with nitrogen, or by applying minerals in foliar sprays.     

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     

Effects of CO2 Enrichment at Different Irradiances on Growth and Yield of Wheat: II. EFFECTS ON KLEIBER SPRING WHEAT TREATED FROM ANTHESIS IN CONTROLLED ENVIRONMENTS IN RELATION TO EFFECTS ON PHOTOSYNTHESIS AND PHOTORESPI RATION

Spring wheat plants were grown in a cage with a glass roof untilthree days after anthesis and then subjected to treatments inconstant environment rooms with any one of all combinationsof four irradiances and two concentrations of carbon dioxide.The photoperiod was 16 h and day/night temperatures 19?C/14?C.Growth and yield of grain were saturated at the two brightestirradiances. Carbon dioxide enrichment from 350 to 1200 mm³dm^–3 increased shoot dry weight and grain yield at finalharvest at all irradiances, by averages of 10.5 (not significant)and 23.5 (significant) percent respectively. However, increasingthe irradiance from 150 to 613 µE m^–2 s^–1caused much larger yield increases (approximately 3-fold). Increasedgrain production by increased light was caused by both increasesin dry weight per grain and by increases in grain number perspikelet. The increase caused by CO₂ enrichment was mainly becauseof increased dry weight per grain. Increase in ear dry weightcaused by CO₂ enrichment took place between 30 and 60 d afteranthesis. The increase in shoot dry weight took place immediatelyafter exposure to increased CO₂ from 3 to 15 d after anthesis.Net photosynthesis by flag leaves on the main shoots was almostdoubled 16 d after anthesis by the CO₂ enrichment even thoughstomatal resistance was also doubled. However, this increasewas not reflected by a proportional increase in yield, probablybecause increased mutual shading by bigger stems and late tillersreduced total assimilation and because of increased respirationby the shoots. The increase in photosynthesis was not due toa decrease in photorespiration but to an increase in gross photosynthesis. Key words: CO₂enrichment, Photosynthesis, Photorespiration     

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.     

Effects of CO2 and Photosynthetic Photon Flux on Yield, Gas Exchange and Growth Rate of Lactuca Sativa L. 'Waldmann's Green'

Knight, S. L. and Mitchell, C. A. 1988. Effects of CO₂ and photosyntheticphoton flux on yield, gas exchange and growth rate of Lactucasativa L. ‘Waldmann’s Green'.—J. exp. Bot.39: 317–328. Enrichment of CO₂ to 46 mmol m^–3 (1 000 mm³ dm^–3)at a moderate photosynthetic photon flux (PPF) of 450 µmolm^–2 s^–1 stimulated fresh and dry weight gain oflettuce leaves 39% to 75% relative to plants at 16 mmol m^–3CO₂ (350 mm³ dm^–3). Relative growth rate (RGR) was stimulatedonly during the first several days of exponential growth. ElevatingCO₂ above 46 mmol m^–3 at moderate PPF had no further benefit.However, high PPF of 880–900 µmol m^–2 s^–1gave further, substantial increases in growth, RGR, net assimilationrate (NAR) and photosynthetic rate (Pn), but a decrease in leafarea ratio (LAR), at 46 or 69 mmol m^–3 (1000 or 1500 mm³dm^–3) CO², the differences being greater at the higherCO₂ level. Enrichment of CO₂ to a supraoptimal level of 92 mmolm^–3 (2000 mm³ dm^–3) at high PPF increased leaf areaand LAR, decreased specific leaf weight, NAR and Pn and hadno effect on leaf, stem and root dry weight or RGR relativeto plants grown at 69 mmol m^–3 CO₂ after 8 d of treatment.The results of the study indicate that leaf lettuce growth ismost responsive to a combination of high PPF and CO₂ enrichmentto 69 mmol m^–3 for several days at the onset of exponentialgrowth, after which optimizing resources might be conserved. Key words: Photosynthesis, relative growth rate, CO₂ enrichment     

Effects of CO2-Enrichment on the Growth of Young Tomato Plants in Low Light

Carbon dioxide-enrichment of young tomato plants grown in controlled-environmentcabinets at low light intensity (14 cal cm^–2 day^–1,visible radiation) increased their net assimilation rates and,initially, relative growth-rates. Subsequently, the relativegrowth-rate fell to near the rate of non-enriched plants, owingto a fall in leaf-area ratio associated with an increase inleaf dry weight/area. Sowing non-enriched plants a few daysearlier to reach the same total dry weight would not have producedidentical plants. The effects of CO₂-enrichment to 1000 vpm could be simulatedby increasing light intensity by approximately one third exceptthat the plants had shorter internodes than those in extra CO₂.This was a morphogenetic effect of light since CO₂-enrichmentitself produced slightly shorter plants than controls for anequivalent total dry weight. CO₂-enrichment did not change the dry-weight distribution inthe plants and had little effect on rate of leaf produoctionor the number of flower primordia. There were no indicationsthat beneficial effects of CO₂-enrichment operated other thanthrough increased photosynthesis.     

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.     

The Influence of Seedling Size and Carbohydrate Status and of Photon Flux Density During Vernalization on Inflorescence Initiation in Onion (AIlium cepa L.)

Experiments were done in controlled conditions to investigatethe relationship of plant weight, leaf number and raising conditionsto inflorescence initiation in onion seedlings. Above a shootdry weight of 0.06 g the spring-sown cv. Rijnsburger could initiateinflorescences, whereas the autumn-sown cv. Senshyu semi-globeYellow needed to be heavier than 0.45 g. Plants raised at aphoton flux density of 200 µmol m^–2S^–1 anda temperature of 25 C required longer to initiate inflorescencesthan plants raised at 600 µmol m^–2S^–1 and17 C which had higher reserve carbohydrate content. The minimumleaf number for inflorescence initiation was larger for plantswith low reserve carbohydrate content. Photon flux densitiesof 50, 100, 200 and 400 µmol m^–2S^–1 duringvernalization at 9 C caused no differences in inflorescenceinitiation in plants previously raised at l7 C and 600 µmolm^–2S^–1 but the lowest photon flux density duringvernalization reduced initiation in plants previously raisedat 25 C and 200 µmol m^–2S^–1.     

Growth and Nitrogen Fixation of Phaseolus vulgaris L. at Two Irradiances 1. Growth

Plants of Phaseolus vulgaris grown at 7 and 28 W m^–2 showedno differences in rate of development of leaves or flowers.At 7 W m-Z plants had longer internodes, more succulent stemsand leaves, higher ratios of shoot:root and greater leaf areasthat those at 28 W m^–2. These differences were establishedprior to detectable differences in photosynthesis and couldpartly be attributed to an increased proportion of far-red light. Although the final d. wt, carbon content, and fruit yield werehigher at 28 W m^–2, plants at 7 W m^–2 apparentlyhad similar relative growth rates and greater photosyntheticefficiency. Dry weight differences are most easily interpretedas resulting from the establishment of an earlier net carbongain at 28 W m^–2 than at 7 W m^–2.     

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.     

Is Partitioning of Dry Weight and Leaf Area Within Dactylis glomerata Affected by N and CO2Enrichment?

We examined changes in dry weight and leaf area within Dactylisglomerata L. plants using allometric analysis to determine whetherobserved patterns were truly affected by [CO₂] and N supplyor merely reflect ontogenetic drift. Plants were grown hydroponicallyat four concentrations of in controlled environment cabinets at ambient (360 µll^–1) or elevated (680 µl l^–1) atmospheric[CO₂]. Both CO₂and N enrichment stimulated net dry matter production.Allometric analyses revealed that [CO₂] did not affect partitioningof dry matter between shoot and root at high N supply. However,at low N supply there was a transient increase in dry matterpartitioning into the shoot at elevated compared to ambient[CO₂] during early stages of growth, which is inconsistent withpredictions based on optimal partitioning theory. In contrast,dry matter partitioning was affected by N supply throughoutontogeny, such that at low N supply dry matter was preferentiallyallocated to roots, which is in agreement with optimal partitioningtheory. Independent of N supply, atmospheric CO₂enrichment resultedin a reduction in leaf area ratio (LAR), solely due to a decreasein specific leaf area (SLA), when plants of the same age werecompared. However, [CO₂] did not affect allometric coefficientsrelating dry weight and leaf area, and effects of elevated [CO₂]on LAR and SLA were the result of an early, transient stimulationof whole plant and leaf dry weight, compared to leaf area production.We conclude that elevated [CO₂], in contrast to N supply, changesallocation patterns only transiently during early stages ofgrowth, if at all. Copyright 2000 Annals of Botany Company Allometric growth, carbon dioxide enrichment, Cocksfoot, Dactylis glomerata L., dry weight partitioning, leaf area ratio, nitrogen supply, shoot:root ratio, specific leaf area     

Effects of elevated carbon dioxide on three montane grass species: I. Growth and dry matter partitioning

Upland grasslands are a major component of natural vegetationwithin the UK. Such grasslands support slow growing relativelystable plant communities. The response of native montane grassspecies to elevated atmospheric carbon dioxide concentrationshas received little attention to date. Of such studies, mosthave only focused on short-term (days to weeks) responses, oftenunder favourable controlled environment conditions. In thisstudy Agrostis caplllaris L.⁵, Festuca vivipara L. and Poa alpinaL. were grown under semi-natural conditions in outdoor open-topchambers at either ambient (340µmol mol^–1) or elevated(680µmol mol^–1) concentrations of atmospheric carbondioxide (CO₂ for periods from 79 to 189 d, with a nutrient availabilitysimilar to that of montane Agrostis-Fescue grassland in Snowdonia,N. Wales. Whole plant dry weight was increased for A. capillarisand P. alpina, but decreased for F. vivipara, at elevated CO₂.Major components of relative growth rate (RGR) contributingto this change at elevated CO₂ were transient changes in specificleaf area (SLA) and leaf area ratio (LAR). Despite changes ingrowth rate at 680 µmol mol^–1 CO₂, partitioningof dry weight between shoot and root in plants of A. capillarisand P. alpina was unaltered. There was a significant decreasein shoot relative to root growth at elevated CO₂ in F. viviparawhich also showed marked discoloration of the leaves and increasedsenescence of the foliage. Key words: Allometry, growth analysis, elevated CO₂, grasses     

Root Distribution, Growth, Respiration, and Hydraulic Conductivity for Two Highly Productive Agaves

Cultivated Agave mapisaga and A. salmiana can have an extremelyhigh above-ground dry-weight productivity of 40 Mg ha^–1yr^–1. To help understand the below-ground capabilitiesthat support the high above-ground productivity of these Crassulaceanacid metabolism plants, roots were studied in the laboratoryand in plantations near Mexico City. For approximately 15-year-oldplants, the lateral spread of roots from the plant base averaged1.3 m and the maximal root depth was 0.8 m, both considerablygreater than for desert succulents of the same age. Root andshoot growth occurred all year, although the increase in shootgrowth at the beginning of the wet season preceded the increasein growth of main roots. New lateral roots branching from themain roots were more common at the beginning of the wet season,which favoured water uptake with a minimal biomass investment,whereas growth of new main roots occurred later in the growingseason. The root: shoot dry weight ratio was extremely low,less than 0.07 for 6-year-old plants of both species, and decreasedwith plant age. The elongation rates of main roots and lateralroots were 10 to 17 mm d^–1, higher than for various desertsucculents but similar to elongation rates for roots of highlyproductive C₃ and C₄ agronomic species. The respiration rateof attached main roots was 32 µmol CO₂ evolved kg^–1dry weight s^–1 at 4 weeks of age, that of lateral rootswas about 70% higher, and both rates decreased with root age.Such respiration rates are 4- to 5-fold higher than for Agavedeserti, but similar to rates for C₃ and C₄ agronomic species.The root hydraulic conductivity had a maximal value of 3 x 10^–7ms^–1 MPa^–1 at 4 weeks of age, similar to A. deserti.The radial hydraulic conductivity from the root surface to thexylem decreased and the axial conductivity along the xylem increasedwith root age, again similar to A. deserti. Thus, although rootsof A. mapisaga and A. salmiana had hydraulic properties perunit length similar to those of a desert agave, their highergrowth rates, their higher respiration rates, and the greatersoil volume explored by their roots than for various desertsucculents apparently helped support their high above-groundbiomass productivity Key words: Crassulacean acid metabolism, productivity, root elongation rate, root system, water uptake     

The Uptake of Phosphate by Plants from Flowing Nutrient Solution: II. GROWTH OF LOLIUMPERENNEL. AT CONSTANT PHOSPHATE CONCENTRATIONS

The effect of phosphate concentration in flowing solution cultureat a range between 0.04 and 32 mmol m^–3 P on the growthof perennial ryegrass was studied in two experiments, each lastingabout 45 d after sowing. Phosphorus contents of seedlings wereaffected by the concentration in solution within about 5 d fromgermination, and dry weight differences were first observedat about 6 d after this. The rate of uptake of phosphate byseedlings was affected by the concentration in solution beforethe root fresh weight or root/emdash shoot ratio had changed.Young plants (less than 4 weeks old) were more sensitive tophosphate concentration in solution than older ones. In conditionsof high rate of growth, older plants required a solution concentrationbetween 0.1 and 0.4 mmol m^–3 P to achieve maximum potentialgrowth rate, whereas for plants of similar age but less dryweight, 0.04 mmol m^–3 P was adequate. Towards the endof the experimental period, plants growing at a nominal solutionconcentration of 0.04 mmol m^–3 P were able to obtain phosphatefrom a solution of about 0.01 mmol m^–3P. Phosphate toxicity was not observed, nor were there visual symptoms(other than reduced growth) of phosphate deficiency in plantswhose growth was limited by phosphate concentration in solution. Key words: Lolium perenne, Phosphate uptake     

Nitrate Reduction by Cassava

Nitrate reductase (NR) was assayed in vivo in cassava (Manihotesculenta Crantz). Activity in the leaves ranged from 0 to 2.51µmole of NO₃^– reduced g^–1 h^–1, withno activity in the younger leaves (leaf 1 on top). NR activitywas localized in the sides and toward the tip of the lobes ofthe leaf. (Received December 10, 1985; Accepted April 8, 1986)     

Effect of Nitrogen Supply on the Grass and Clover Components of Simulated Mixed Swards Grown under Favourable Environmental Conditions I. Carbon Assimilation and Utilization

Simulated mixed swards of Perennial Ryegrass (Lolium perenneL.) cv. S23 and White clover (Trifolium repens L.) cv. S100were grown from seed under a constant 20 °C day/15 °Cnight temperature regime and their growth and carbon economyexamined. The swards received a nutrient solution daily, whichcontained either High (220 mg l^–1) or Low (10 mg l^–1)nitrate N. Rates of canopy photosynthesis and respiration, and final drymatter yields were similar in the two treatments although theproportions of grass and clover differed greatly. The Low-Nswards were made up largely of clover. The grass plants in theseswards had high root: shoot ratios and low relative photosyntheticrates – both signs of N deficiency – and were clearlyunable to compete with the vigorously growing Low-N clover plants.These had higher relative growth rates and dry matter yieldsthan their High-N counterparts. In the High-N swards clovercontributed around 50 per cent to the sward dry weight throughoutthe measurement period despite having a smaller proportion ofits dry weight in photosynthetic tissue (laminae) than grassover much of it. The latter was compensated for, initially bya higher specific leaf area than grass, and later by a higherphotosynthetic rate per unit leaf weight. The results are discussedin relation to observed declines in the clover content of swardsafter the addition of nitrogen fertilizer in the field. Trifolium repens, white clover, Lolium perenne, perennial ryegrass, nitrogen, photosynthesis, carbon balance     

C3 and CAM Photosynthetic Characteristics of the Submerged Aquatic Macrophyte Littorella uniflora: Regulation of Leaf Internal CO2 Supply in Response to Variation in Rooting Substrate Inorganic Carbon Concentration

The relationships between CO₂ concentrating mechanisms, photosyntheticefficiency and inorganic carbon supply have been investigatedfor the aquatic macrophyte Littorella uniflora. Plants wereobtained from Esthwaite Water or a local reservoir, with thelatter plants transplanted into a range of sediment types toalter CO₂ supply around the roots. Free CO₂ in sediment-interstitial-waterranged from 1–01 mol m^–3 (Esthwaite), 0.79 mol m^–3(peat), 0.32 mol m^–3 (silt) and 0–17 mol m^–3(sand), with plants maintained under PAR of 40 µmol m^–2s^–1. A comparison of gross morphology of plants maintained underthese conditions showed that the peat-grown plants with highsediment CO₂ had larger leaf fresh weight (0–69 g) andtotal surface area (223 cm² g^–1 fr. wt. including lacunalsurface area) than the sand-grown plants (0.21 g and 196 cm²g^–1 fr. wt. respectively). Root fresh weights were similarfor all treatments. In contrast, leaf internal CO₂ concentration[CO₂], was highest in the sand-grown plants (2–69 molm^–3, corresponding to 6.5% CO₂ in air) and lowest inthe Esthwaite plants (1–08 mol m^–3). Expressionof CAM in transplants was also greatest in the low CO₂ regime,with H⁺ (measured as dawn-dusk titratable acidity) of 50µmolg^– fr. wt., similar to Esthwaite plants in natural sediment.Assuming typical CAM stoichiometry, decarboxylation of malatecould account largely for the measured [CO₂]₁ and would makea major contribution to daytime CO₂ fixation in vivo. A range of leaf sections (0–2, 1–0, 5–0 and17–0 mm) was used to evaluate diffusion limitation andto select a suitable size for comparative studies of photosyntheticO₂ evolution. The longer leaf sections (17.0 mm), which weresealed and included the leaf tip, were diffusion-limited witha linear response to incremental addition of CO₂ and 1–0mol m^–3 exogenous CO₂ was required to saturate photosynthesis.Shorter leaf sections were less diffusion-limited, with thegreatest photosynthetic capacity (36 µmol O₂ g^–1 fr. wt. h^–1) obtainedfrom the 1.0 mm size and were not infiltrated by the incubatingmedium. Comparative studies with 1.0 mm sections from plants grown inthe different sediment types revealed that the photosyntheticcapacity of the sand-grown plants was greatest (45 µmolO₂ g^–1 fr. wt. h^–1) with a K_0.5 of 80 mmol m^–3.In terms of light response, saturation of photosynthesis intissue slices occurred at 850–1000 µmol m^–2s^–1 although light compensation points (6–11 µmolm^–2s^–1) and chlorophyll a: b ratios (1.3) were low.While CO₂ and PAR responses were obtained using varying numbersof sections with a constant fresh weight, the relationshipsbetween photosynthetic capacity and CO₂ supply or PAR were maintainedwhen the data were expressed on a chlorophyll basis. It is concludedthat under low PAR, CO₂ concentrating mechanisms interact inintact plants to maintain saturating CO₂ levels within leaflacunae, although the responses of the various components ofCO₂ supply to PAR require further investigation. Key words: Key words-Uttorella uniflora, internal CO₂ concentration, crassulacean acid metabolism, root inorganic carbon supply, CO₂ concentrating mechanism     

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