The Growth and Development of Simulated Swards of Perennial Ryegrass: II. Carbon Assimilation and Respiration in a Seedling Sward

The rates of net photosynthesis (P_n,c) in the light (85 W m^–2visible), and respiration in the dark, of a simulated swardof S24 ryegrass were measured for 12 weeks during its developmentfrom a collection of two-leaved seedlings to a closed canopywith an LAI of 23 (15 of green leaf laminae). By the sixth week light interception was complete (LAI = 10.6)and P_n,c had risen to 24 mg CO₂ dm^–2 h^–1, similarto rates recorded in the field. Photosynthetic functions (lightresponse curves) showed that the swards remained unsaturatedup to energy receipts of almost 400 W m^–2, whereas singleleaves were light saturated at about 130 W m^–2. Earlyin the development of the sward LAI had a greater effect onP_n,c than radiation receipt, later the reverse was true. Thegrowth habit of the sward ranged from moderately erect (an Svalue of 0.72) to moderately prostrate (‘S’ = 0.37),while the ability of the two youngest fully expanded leaveson a tiller to make use of light in photosynthesis declinedas the sward increased in density from values of A max of 20to 5 mg CO₂ dm^–2 h^–1. By varying the values of Sand A max fed into a model of canopy photosynthesis, withinthe above limits, it was demonstrated that, in practice, A maxis a greater determinant of canopy photosynthesis than S, exceptat low LAI where a prostrate sward has a marked advantage overan erect one. The rate of dark respiration rose as the swards increased inweight, although not in proportion to it, until the ninth weekwhen a ceiling yield of live plant tissue was reached. Respiratorylosses from the sward came almost equally from a component associatedwith maintenance (R_m) and one associated with growth (R_g). Therate of Rm was estimated to be about 0.014 g day^–1 pergram of plant tissue, and that of Ra about 0.25 g per gram ofnew tissue produced—both close to theoretical values.The measured dry matter production curve of the swards was comparedwith that estimated from the gas analysis data. Similarly therates of gross photosynthesis estimated from the gas analysisdata were compared with the predictions of the mathematicalmodel. In both cases the fit was reasonably good. A balancesheet was drawn up; of every 100 units of carbon fixed, 45 werelost in respiration and 16 as dead leaf, 5 ended up in the rootand 6 in the stubble; only 28 remained as harvestable live leaftissue.     

Effect of Temperature and Nitrogen Supply on the Growth of Perennial Ryegrass and White Clover. 1. Carbon and Nitrogen Economies of Mixed Swards at Low Temperature

Simulated mixed swards of perennial ryegrass (Lolium perenneL. cv. S23) and white clover (Trifolium repens L. cv. S100)were grown from seed under a constant 10°C day/8°C nighttemperature regime and their growth, and carbon and nitrogeneconomies examined. The swards received a nutrient solution,every second day, which contained either high (220 µgg^–1) or low (40 µg g^–1) nitrate N. The High-N swards had rates of canopy photosynthesis and drymatter production (over the linear phase of growth) similarto those previously shown by mixed swards at high temperature.The Low-N swards grew more slowly; canopy photosynthesis, ata given LAI, was similar to that at High-N but lower LAI's weresustained. Clover increased its contribution to total carbonuptake and total dry weight throughout the period in the Low-Ntreatment and, despite the fact that grass took up most of theavailable nitrate, clover maintained a consistently higher Ncontent by virtue of N₂-fixation. At High-N, grass dominated throughout the measurement period.Earlier, when plants grew as spaced individuals, clover grewless well than grass, but once the canopy was closed it hada similar relative growth rate and thus maintained a steadyproportion of total sward dry weight. It is proposed that earlyin the development of the crop, leaf area production is thelimiting factor for growth, and that in this respect cloveris adversely affected by low temperature relative to grass.Later, as the LAI of the crop builds up, and the canopy becomesfully light intercepting, net canopy photosynthesis plays amore dominant role and here the higher photosynthetic rate perunit leaf area of the clover is crucial. Trifolium repens, white clover, Lolium perenne, perennial ryegrass, low temperature, nitrogen, photosynthesis     

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     

Seasonal Changes in the Physiology of S24 Perennial Ryegrass (Lolium perenne L.). 1. Response of Leaf Extension to Temperature during the Transition from Vegetative to Reproductive Growth

The potential for leaf extension of plants of Lolium perennecv S24 growing in small artificial communities under naturalconditions was measured as the plants progressed from the vegetativeto the reproductive state In two consecutive years, 1975 and 1976, ‘simulated swards’were sown in autumn and overwintered in an open, unheated glasshouseIndividual swards from the batch sown in 1975 were brought into a growth room on two occasions in spring 1976 to measuretheir potential for leaf extension at a range of temperatures(5–20 °C) Individual swards from the batch sown inautumn 1976 were brought in to the growth room on 15 occasionsbetween November 1976 and May 1977 and their potential for leafextension was measured at a single temperature of 15 °CFrequent dissections were made in both years to describe changesin the developing apex. The potential for leaf extension at 15 °C decreased fromc 17 mm day^–1 in November to c 10 mm day^–1 in mid-winter.In January, the potential rapidly increased threefold to reach30mm day^–1 by mid February The increase began coincidentwith the earliest stages of floral initiation and was completedby the time of double-ridge formation Spring-grown vegetativeplants, however, showed potential rates of < 20 mm day^–1at 15 °C The results are discussed in relation to reproductive developmentand to changes in the carbohydrate strategy of the plants inearly spring Lolium perenne L perennial ryegrass, leaf extension, temperature response     

Effect of Previous Defoliation Regime and Mineral Nitrogen on Regrowth in White Clover Swards: Photosynthesis, Respiration, Nitrogenase Activity and Growth

Small swards of white clover (Trifolium repens L.) cv. Haifawere grown in solution culture in a controlled environment at24 °C day/18 °C night and receiving 500 µE m^-2S^–1 PAR during a 14-h photoperiod. The swards were cuteither frequently (10-d regrowth periods) or infrequently (40-dregrowth) over 40 d before being cut to 2 cm in height. Halfof the swards received high levels of nitrate (2–6 mMN in solution every 2 d) after defoliation while the othersreceived none. Changes in d. wt, leaf area and growing pointnumbers were recorded over the following 10 d. CO₂ exchangewas measured independently on shoots and roots and nitrogenase-linkedrespiration was estimated by measuring nodulated root respirationat 21% and 3% oxygen in the root atmosphere. There was a general pattern in all treatments consisting ofan initial d. wt loss from roots and stubble and reallocationto new leaves, followed by a period of total d. wt gain andrecovery, to a greater or lesser extent, of weight in non-photosyntheticparts. Frequently cut swards had a smaller proportion of theirshoot d. wt. removed by cutting and had a greater shoot d. wt,growing point number and leaf area at the start of the regrowthperiod. As a result of these differences, and also because ofdifferences in relative growth rates, frequently cut swardsmade more regrowth than infrequently cut. Initial photosyntheticrates were higher in frequently cut swards, although the laminaarea index was very low, and it was concluded that stolons andcut petioles made a significant contribution to carbon uptakeduring the first few d. Infrequently cut swards continued toallocate carbon to new and thinner leaves at the expense ofroots and stubble for longer than frequently cut swards andas a result achieved a similar lamina area index after 10 d. Nitrogenase-linked respiration was low in all treatments immediatelyafter cutting: frequently cut swards receiving no nitrate maintainedhigh nitrogenase activity, whereas recovery took at least 5d in infrequently cut swards. Swards which received nitrateafter cutting maintained only low rates of nitrogenase-linkedrespiration and their total nodulated root respiration overthe period was lower than those receiving no nitrogen: greaterregrowth in nitrate fed swards over the 10 d compared to N₂-fixingswards was in proportion to this lower respiratory burden. White clover (Trifolium repens L.), defoliation, regrowth, nitrogen, photosynthesis, respiration, nitrogenase-activity     

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 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     

Correlative Inhibition of Lateral Bud Growth in Phaseolus vulgaris L. Ethylene and the Physical Restriction of Apical Growth

Restriction of apical growth in Phaseolus by enclosing the upperpart of the shoot in sealed or ventilated tubes induced developmentof axillary buds beneath the enclosure. Enclosed parts of shootsshowed a reduction of leaf growth and, in experiments wherethe tubes were sealed, of internode extension. Enclosure ofthe shoots in large vessels that did not restrict leaf expansion,but which contained 0?5 vols 10^–6 ethylene, similarlyinduced axillary bud growth. Analysis of the gaseous extractof physically restricted shoots showed a 2?5-fold increase inethylene concentration. The results suggest involvement of ethylenein the release of correlative inhibition brought about by physicalrestriction of apical growth.     

Effect of Salinity on Growth, Nodulation and Nitrogen Yield of Chickpea (Cicer arietinum L.)

Chickpea cultivar ILC 482 was inoculated with salt-tolerantRhizobium strain Ch191 in solution culture with different saltconcentrations added either immediately with inoculation or5 d later. The inhibitory effect of salinity on nodulation ofchickpea occurred at 40 dS m^–1 (34.2 mol m^–3 NaCl)and nodulation was completely inhibited at 7 dS m^–1 (61.6mol m^–3 NaCl); the plants died at 8 dS m^–1 (71.8mol m^–3 NaCl). Chickpea cultivar ILC 482 inoculated with Rhizobium strain Ch191^spcstrwas grown in two pot experiments and irrigated with saline water.Salinity (NaCl equivalent to 1–4 dS m^–1) significantlydecreased shoot and root dry weight, total nodule number perplant, nodule weight and average nodule weight. The resultsindicate that Rhizobium strain Ch191 forms an infective andeffective symbiosis with chickpea under saline and non-salineconditions; this legume was more salt-sensitive compared tothe rhizobia, the roots were more sensitive than the shoots,and N₂ fixation was more sensitive to salinity than plant growth. Key words: Cicer arietinum, nodulation, N₂ fixation, Rhizobium, salinity     

Effect of Elevated CO2 on the Photosynthesis, Respiration and Growth of Perennial Ryegrass

Single, seed-grown plants of ryegrass (Lolium perenne L. cv.Melle) were grown for 49 d from the early seedling stage ingrowth cabinets at a day/night temperature of 20/15 C, witha 12 h photoperiod, and a CO₂ concentration of either 340 or680µI 1^–1 CO₂. Following complete acclimation tothe environmental regimes, leaf and whole plant CO₂ effluxesand influxes were measured using infra-red gas analysis techniques.Elevated CO₂ increased rates of photosynthesis of young, fullyexpanded leaves by 35–46% and of whole plants by morethan 50%. For both leaves and whole plants acclimation to 680µI^–1 CO₂ reduced rates of photosynthesis in bothCO₂ regimes, compared with plants acclimated to 340µll^–1. There was no significant effect of CO₂ regime onrespiration rates of either leaves or whole plants, althoughleaves developed in elevated CO₂ exhibited generally lower ratesthan those developed in 340µI I^–1 CO₂. Initially the seedling plants in elevated CO₂ grew faster thantheir counterparts in 340µI I^–1 CO₂, but this effectquickly petered out and final plant weights differed by onlyc. 10%. Since the total area of expanded and unexpanded laminaewas unaffected by CO₂ regime, specific leaf area was persistently13–40% lower in elevated CO₂ while, similarly, root/shootratio was also reduced throughout the experiment. Elevated CO₂reduced tissue nitrogen contents of expanded leaves, but hadno effect on the nitrogen contents of unexpanded leaves, sheathsor roots. The lack of a pronounced effect of elevated CO₂ on plant growthwas primarily due to the fact that CO₂ concentration did notinfluence tiller (branch) numbers. In the absence of an effecton tiller numbers, any possible weight increment was restrictedto the c. 2.5 leaves of each tiller. The reason for the lackof an effect on tillering is not known. Key words: Lolium perenne, ryegrass, elevated CO₂, photosynthesis, respiration, growth, development     

Structure and Function of Oak Forests in Central Himalaya. I. Dry Matter Dynamics

The present study deals with structure and functioning of threeareas of Himalayan oak forest. Low- and mid-altitude oaks, namelyQuercus leucotrichophora, and Quercus floribunda, form predominantevergreen forests in Central and Western Himalaya. The totaltree basal cover ranged between 33·89 m² ha^–1 (Q.floribunda site) to 36·83 m² ha^–1 (Q. leucotrichophorasite). The density ranged between 570 and 760 individuals ha^–1.Allometric equations relating biomass of different tree componentsto GBH (girth at breast height) were significant with the exceptionof leaf biomass in Q. leucotrichophora and Rhododendron arboreum.Total vegetation biomass (29·40–467·0 tha^–1) was distributed as 377·1 t ha^–1 intrees, 5·40 t ha^–1 in shrubs and 1·23 tha^–1 in herbs. Total forest floor biomass ranged between4·6 and 6·2 t ha^–1. Of the total annuallitter fall (4·7–4·8 t ha^–1), 77·5% was contributed by leaf litter, 17·8 % by wood litterand 4·7 % by miscellaneous litter. Turnover rate of treelitter varied from 0·66 to 0·70. Net primary productionof total vegetation ranged between 15·9 and 20·6t ha^–1 yr^–1, of which the contribution of trees,shrubs and herbs was 81·2 %, 8·6 % and 10·2%, respectively. A compartment model of dry matter on the basisof mean data across sites was developed to show dry matter storageand flow of dry matter within the system. Quercus leucotrichophora forest, Q. floribunda forest, Q. lanuginosa forest, biomass, litter fall, net primary production, compartmental transfer     

Influence of Endophyte and Water Regime Upon Tall Fescue Accessions. I. Growth Characteristics

Superior growth and persistence has been reported in endophyte-infectedgrasses; however, findings may have been confounded by experimentconditions including plant genotype. A controUed-environmentstudy was designed to address some growth characteristics offour tall fescue (Festuca arundinacea Schreb.) accessions asinfluenced by endophyte (Acremonium coenophiahim Morgan-Joneset Gams) and water regime. Endophyte-infected plants were collected,vegetatively propagated and some treated with propiconazole(11 kg a.i. ha^–1) to develop non-infected isolines ofeach accession. The phenotypically diverse accessions, eachrepresented by infected and non-infected isolines, were grownwith adequate (–0–03 MPa), or a series of deficit(<–1·5 MPa) and recovery water regimes, replicatedthree times. Plant growth characteristics were measured during(leaf elongation and tillering) and upon conclusion (phytomassproduction, tillering, and leaf area) of the study. Leaf elongation,as a function of leaf length, was significantly different amongaccessions, and generally decreased with water deficit althoughsome non-infected isolines were not affected. Water deficitdepressed tiller production in virtually all accessions whileendophyte effects depended upon accession. Leaf blade yieldwas not significantly influenced by endophyte status or interactionof endophyte, with water regime and accession; however, pseudostem(stem base and leaf sheath), root and dead leaf yields wereaffected in some cases. Non-structural carbohydrate concentrationin all plant parts except roots, was decreased by water deficit,whereas root non-structural carbohydrate concentration tendedto increase with water deficit. Non-structural carbohydratesof all plant parts was not influenced by endophyte status. Tallfescue-endophyte association responses vary due to genotype,therefore a simple generalization of endophyte impact upon tallfescue productivity and persistence is not possible based uponthe results of this study Festuca arundinacea Schreb., Acremonium coenophiahim Morgan-Jones et Gams, leaf elongation, phytomass production, tillering, water deficit, non-structural carbohydrate     

Effects of Nitrogen Fertilizer on Growth and Yield of Spring Wheat

Nine amounts of nitrogen fertilizer, ranging from 0 to 200 kgN ha^–1, were applied to spring wheat cv. Kleiber in the3 years 1972-1974. In 1972 grain dry weight with 125 kg N ha^–1or more was 100 g m^–2 (23 per cent) greater than withoutnitrogen. Grain yield was unaffected by nitrogen in the otheryears. Leaf area at and after anthesis was increased throughoutthe range of nitrogen tested, most in 1972 and least in 1973.Consequently, the addition of 200 kg N ha^–1 decreasedthe amount of grain produced per unit of leaf area by approximately25 per cent in all years. The dry weight of leaves and stems at anthesis and maturitywas increased by nitrogen in all years, similarly to leaf area.However, the change in stem dry weight between anthesis andmaturity was not affected by nitrogen; stems increased in dryweight for about 20 days after anthesis and then decreased tovalues similar to those at anthesis. The uptake of CO₂ per unit area of flag leaf or second leaf(leaf below the flag leaf) was slightly decreased by nitrogenwhen the increase in leaf area caused by nitrogen appreciablydecreased the light intensity at the surface of these leaves.In spite of such decreases the CO₂ absorbed by flag and secondleaves per unit area of land was always increased by nitrogen,and relatively more than was grain yield. It is suggested that increases in respiratory loss of CO₂ withincreasing nitrogen fertilizer may explain why nitrogen increasedvegetative growth and leaf area relatively more than grain yield.     

Respiratory Efflux in Relation to Temperature of Simulated Swards of Perennial Ryegrass with Contrasting Soluble Carbohydrate Contents

Fully light-intercepting simulated swards of S24 perennial ryegrasswere exposed to contrasting environmental conditions in a growthroom for 4 days. Half experienced 20 h days of 120 Wm^–2(400–700. nm) and 5 °C, and came to have a WSC (watersoluble carbohydrate) content of 235 mg g^–1 and half 4h days of 20 Wm^–2 and 25 °C leading to a WSC of 25mg g^–1. Their rates of CO₂ efflux were monitored at anumber of temperatures during an 8 h dark period; half experiencedincreasing (5–30 °C) and half decreasing (30–5°C) temperatures. The ‘high’ WSC swards hadrespiration rates of 3.7 mg CO₂ g^–1 (d. wt) h^–1at 15 °C, and the ‘low’ swards 0.8 mg CO₂ g^–1h^–1. The order in which the temperatures were experiencedwas immaterial. Even the ‘low’ WSC swards showedno evidence of a respiratory decline during the dark periodthat could be attributed to substrate shortage. The relationshipbetween temperature and CO₂ efflux was best represented by logisticcurves. Even so, a Q₁₀ of 2 fitted the data reasonably well,at least up to 20 °C, and has practical advantages wheninterpolating estimated between measured values of respirationin the construction of a carbon balance sheet. Lohum perenne L., ryegrass, respiration, temperature, Q₁₀, soluble carbohydrate content, simulated sward     

Effect of External Supply of Growth Substances on Axillary Proliferation and Development in Dioscorea bulbifera

Bulbil development in cultured nodes of D. bulbifera proceededin the absence of growth substances from the medium. When IAAwas incorporated into the medium at the concentrations of 5mg l^–1 and 10 mg l^–1 the cultured nodes producedlarger bulbils than in its absences. When the concentrationof IAA was increased to 15 mg l^–1, however, the culturednodes produced a callus instead of a properly organized bulbil.The dry weight of bulbils increased when kinetin was added tothe medium at the concentrations of 0.05, 0.5, and 2.5 mg l^–1.The greatest increase was with 0.5 mg l^–1 kinetin. Onincreasing the concentration of kinetin in the medium to 5.0mg l^–1 the tissue produced had smaller dry weight thanthose produced in the absence of growth substances. Additionof different combinations of IAA and kinetin to the basal mediumresulted in the production of normal bulbils, roots, and shootsin some instances (suitable combinations) and in the productionof callus and abnormal shoots in others (non suitable combinations).     

The Growth and Survival of Severely-shaded Tillers in Lolium perenne L.

The effect of shading a single tiller to below its compensationpoint for a period of 5 weeks in vegetative plants of Loliumperenne L. cv. S23, was studied in two different experimentseach employing two light regimes, one of which was common toboth experiments. In the first experiment tillers in the axils of the first leafwere shaded three weeks from appearance at both 40 and 70 Wm^–2. None of the shaded tillers died and they continuedto produce new leaves and increase in dry weight but at a reducedrate. In the second experiment, tillers with one emerged leafin any leaf axil position were shaded at 70 W m^–2 andin a treatment in which light was reduced to 13 W m^–2after initial growth at 70 W m^–2. As in the first experimentall shaded tillers survived at 70 W m^–2 but in the 70 13 W m^–2 transfer regime all shaded tillers died. In the second experiment shaded tillers in both light regimeswere supplied with ¹⁴C-assimilate by translocation from theremainder of the plant but in the 70 13 W m^–2 the initialsupport was withdrawn within 5 weeks of shading. The results are discussed in terms of the physiological relationshipsbetween the tillers of the grass plant. Lolium perenne L., growth of tillers, survival of tillers, effect of light     

Photosynthesis and Degree of Polymerization of Fructan during Reproductive Growth of Meadow Fescue at two Temperatures and two Photon Flux Densities

Accumulation of dry weight was measured in plant parts of meadowfescue (Festuca pratensis Huds.) that was grown at 16/11 °Cor 26/21 °C and with 20 or 60 nE cm^–2 s^–1 photosyntheticallyactive radiation. Plants reached anthesis about 3 weeks laterat 16/11 °C than at 26/21 °C and had then a higher proportionof dry weight in inflorescences and less in leaf blades. Growthtemperature had little effect on CO₂ exchange rate (CER) butplants grown at 60 nE cm^–2 s^–1 had higher CER thanthose grown at 20 nE cm^–2 s^–1. The concentration of water-soluble carbohydrates (WSC) at similargrowth stages was usually higher at 16/11°C than at 26/21°C.High radiation also led to higher WSC in stem and leaf tissue.Root tissue changed least and WSC did not exceed 10% of dryweight during the experiment. In all tissues, when WSC was high,the fructans were distributed into a group with a high degreeof polymerization (DP) and another with a low DP. The low DPgroup included sucrose, reducing sugars and fructans up to about20 units long. An apparent threshold concentration of WSC wasnecessary for synthesis of the high DP fructans. This concentrationwas near 12% for leaf tissue, about 6% for stem base tissue,and 2.5% for root tissue. The average apparent DP of the highDP fructan group was 43 to 50 for leaf tissue, 31 to 93 forstem base tissue, and 27 to 31 for roots. These characteristicsappeared to be mostly tissue dependent with less effect fromtemperature and radiation. Key words: Fructans, Meadow fescue, Environmental effects, Dry weight distribution     

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     

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     

Microclimate, Photosynthesis and Growth of Lucerne (Medicago sativa L.). II. Canopy Structure and Growth

The growth of lucerne var. Europe was examined in the fieldduring 1976. The annual dry matter production of unirrigatedlucerne during 1976, with no nitrogen fertilizer application,was 82.5 per cent greater than unirrigated S.24 perennial ryegrass,with a nitrogen application of 384 kg ha^–1. The mean aboveground growth rate of lucerne was 7.3 g DM m^–2 day^–1between March and early June, of which stem material contributeda maximum of 76.5 per cent. Significant losses of leaves andstems occurred from the end of April, indicating a loss of potentialforage material. Nitrogen analyses of the above ground crop suggested that in56 days lucerne yielded 10.7 per cent more nitrogen than didS.24 annually with a nitrogen fertilizer addition of 280 kgha^–1. Between 13 and 57 per cent of the daily photosynthate is translocatedbelow ground. Medicago sativaL, lucerne, dry matter production, canopy structure, nitrogen analyses