Origin of Foliar Nitrogen and Changes in Free Amino-Acid Composition and Content of Leaves, Stubble, and Roots of Perennial Ryegrass During Re-growth after Defoliation

Nitrogen re-mobilization and changes in free amino acids werestudied as a function of time in leaves, stubble, and rootsduring ryegrass (Lolium perenne L.) re-growth. Experiments with¹⁵N labelling clearly showed that during the first days nearlyall the nitrogen in new leaves came from organic nitrogen re-mobilizedfrom roots and stubble. On the days of defoliation, stubblehad the highest content of free amino acids with 23 mg per gdry weight against 15 mg and 14 mg in leaves and roots, respectively.The major amino acids in leaves were asparagine (23% of totalcontent in free amino acids), aminobutyrate, serine, glutamine,and glutamate (between 7% and 15%) whereas in roots and stubblethe contribution of amides was high, especially asparagine (about50%). Re-growth after cutting was associated with a rapid increaseof the free amino acid content in leaves, with a progressivedecrease in roots while stubble content remained virtually unchanged.In leaves, asparagine increased from the first day of re-growth,while the aspartate level remained unchanged and glutamine increasedstrongly on the first day but decreased steadily during thenext few days of re-growth. Asparagine in stubble and rootschanged in opposite directions: in stubble it tended to increasewhereas in roots it clearly decreased. In contrast, stubbleand roots showed a similar decrease in glutamine. In these twoplant parts, as in leaves, aspartate remained at a low level.Results concerning free amino acids are discussed with referenceto nitrogen re-mobilization from source organs (stubble androots) to the sink organ (regrowing leaves). Key words: Lolium perenne L, re-growth, nitrogen, free amino acids, glutamine, asparagine     

The Uptake of Gaseous Ammonia by the Leaves of Italian Ryegrass

Lockyer, D. R. and Whitehead, D. C. 1986. The uptake of gaseousammonia by the leaves of Italian ryegrass.—J. exp. Bot.37: 919–927. Plants of Italian ryegrass (Lolium multiflorum Lam.) grown insoil with two rates of added ¹⁵N-labelled nitrate were exposed,in chambers, for 40 d to NH₃ in the air at concentrations of16, 118 and 520 µg m^–3. At the highest concentrationof NH₃, this source provided 47?3% of the total nitrogen inplants grown with the lower rate of nitrate addition (100mgN kg^–1 dry soil) and 35?2% with the higher rate (200mgN kg^–1 dry soil) At the intermediate concentration ofNH₃, the contributions to total plant N were 19?6% and 10?8%,respectively, at low and high nitrate while, at the lowest concentrationof NH₃, they were 5?1% and 32%. Most of the N derived from theNH₃ remained in the leaves, but some was transported to theroots. The amount of N derived from the NH³ that was presentin the leaves was not reduced by washing the leaves in waterat pH 5?0 before harvesting, indicating that the N was assimilatedby the plant and not adsorbed superficially. Rates of uptakeof NH₃ per unit leaf area ranged from 1?7 µg dm^–2h^–1 at a concentration of 16 µg m^–3 to 29?0µg dm^–2 h^–1 at a concentration of 520 µgm^–3 and with the lower rate of nitrate addition. Increasingthe supply of nitrate to the roots slightly reduced the rateof uptake of NH₃ per unit leaf area. Uptake of N from the higherrate of nitrate was reduced at the highest concentration ofNH₃ in the air. Key words: Ammonia, nitrogen, leaf sorption, Lolium multiflorum     

Growth of Ryegrass (Lolium perenne L.) Exposed to SO2: III. EFFECTS ON FREE AND STORAGE CARBOHYDRATE CONCENTRATIONS

Exposure of ryegrass (Lolium perenne L.) cv. S23 to 0, 50, and400 µg m^–3 SO₂ for an initial 29 d (first harvest),and for an additional 22 d period of regrowth (second harvest),resulted in distinct alterations in carbohydrate metabolismat each harvest. At the first harvest, exposure to 50 µgm^–3 increased concentrations of free and total carbohydrates,whereas exposure to 400 µg m^–3 resulted in concentrationshardly different from those in control plants. At both SO₂ concentrations,more assimilate was retained as free carbohydrate rather thanas storage carbohydrate. Comparison of assimilate distributionat the end of the light, and at the end of the dark period atthe first harvest led to the conclusion that light-mediatedmetabolism is more sensitive to SO₂ exposure than dark metabolism,and that assimilate distribution might be controlled by at leasttwo processes exhibiting different SO₂ sensitivities.     

The Influence of the Concentration of Gaseous Ammonia on its Uptake by the Leaves of Italian Ryegrass, with and without an Adequate Supply of Nitrogen to the Roots

Whitehead, D. C. and Lockyer, D. R. 1986. The influence of theconcentration of gaseous ammonia on its uptake by the leavesof Italian ryegrass, with and without an adequate supply ofnitrogen to the roots.—J. exp. Bot. 38: 818–827. Plants of Italian ryegrass (Lolium multiflorum Lam.) were grownin pots of soil with two rates of ¹⁵N-labclled nitrate, oneproviding adequate, and the other less than adequate, N formaximum growth. After 25 d in a controlled environment cabinet,the plants were transferred to chambers and exposed for 33 dto NH₃in the air at one of nine concentrations ranging from14 to 709 µg NH₃ m^–3. Increasing the concentrationof NH₃ in the air increased the dry weight of the shoots ofplants grown at the lower but not the higher rate of nitrate.The content of total N in the plant shoots (% dry weight) waslinearly related to NH₃ concentration; at 709 µg NH₃ andin both sets of plants it was more than double the content at14 µg NH₃ m^–3. Calculations, based on ¹⁵N enrichment,indicated that the amount of N taken up from the NH₃ per unitleaf area increased linearly with increasing concentration ofNH₃ in the air uptake (µg dm^–2 h^–1) = 0.1009xat the lower rate of nitrate and 0-0829x at the higher rateof nitrate, where x is the concentration of NH₃ in the air expressedas µg NH₃m^–3. The proportion of the total plant N that was derived from theNH₃ ranged from 4?0% at a concentration of 14 µg NH₃ m^–3with the higher rate of nitrate addition to 77?5% at a concentrationof 709 µg m^–3 with the lower rate of nitrate addition.The proportions of the total N in the water-insoluble proteinof the leaf tissue that were derived from nitrate and gaseousNH₃ were similar to the proportions in the whole leaf material. Key words: Ammonia, nitrogen, leaf sorption, Lolium multiflorum     

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     

Studies on the Effect of Sulphur Dioxide on Perennial Ryegrass (Lolium perenneL.): I. CHARACTERISTICS OF FUMIGATION SYSTEM AND PRELIMINARY EXPERIMENTS

The characteristics of a wind tunnel fumigation system in whichplants can be exposed to air pollutants under controlled conditionsover prolonged time periods and at near ambient wind speedsare described. Preliminary experiments exposing perennial ryegrass(Lolium perenne L.) to 650, 700, and 2600 µg SO₂ m^–3showed (i) the consistency of performance of the system and(ii) the lack of correlation in relative response of individualclones to acute and chronic fumigation. The results obtainedare compared with those of other research groups.     

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 Temperature and Nitrogen Supply on the Growth of Perennial Ryegrass and White Clover. 2. A Comparison of Monocultures and Mixed Swards

White clover (Trifolium repens L.) and Perennial ryegrass (Loliumperenne L.) plants were grown, in Perlite, in simulated swardsas either monocultures or mixtures of equal plant numbers. Theywere supplied with a nutrient solution either high (220 µgg^–1) or low (40 µg g^–1) in ¹⁵N-labelled nitrateand grown to ceiling yield at either high (20°C day/15°Cnight) or low (10°C day/8°C night) temperature. Temperature had little effect on the maximum rates of grosscanopy photosynthesis which were similar in High-N grass andHigh-N and Low-N clover monocultures. However these maxima werereached more slowly in clover than grass, and more slowly atlow rather than high temperature. Nitrogen supply increasedphotosynthesis in grass but not in clover. Clover had higherN contents than grass in all four treatments, although in anygiven treatment its N content was lower, and contribution ofN₂-fixation relative to nitrate uptake higher, in mixture thanin monoculture. Conversely, grass had higher N contents in mixturethan monoculture, because more nitrate was available per plantand not because of transfer of biologically fixed N from clover. Under Low-N, clover outyielded grass in mixture, particularlyat high temperature. The grass plants in the Low-N mixtureshad higher N contents and higher SLA, LAR and shoot: root ratiosthan those in monoculture. It is proposed that competition forlight is the cause of the low relative yield and negative aggressivityof grass in these swards. Under High-N, grass outyielded cloverin monoculture and mixture, at both temperatures but particularlyat low temperature when grass had a high aggressivity. Nitrogenand yield component analyses shed no light on clover's apparentlylow competitive ability and evidence is drawn from the previouspaper to demonstrate that grass grew faster than clover onlyas spaced individuals during non-com petitive growth. The relativemerits of measures of competitive ability based on final harvestdata and physiological data taken over a growth period are discussed. Trifolium repens L., white clover, Lolium perenne, perennial ryegrass, competition, temperature, nitrogen     

Growth of Ryegrass (Lolium perenne L.) Exposed to SO2: II. CHANGES IN THE DISTRIBUTION OF PHOTO ASSIMILATED 14C

Perennial ryegrass (Lolium perenne L.) cv. S23 was exposed to0, 50, and400 µg m– ³ SO₂ for a 29 d period, harvested,and then exposed under the same regime for a further 22 d periodof regrowth. Leaves from plants representing each exposure concentrationwere photosynthetically fed ¹⁴CO₂ for 5 min at the end of eachperiod. A significant increase in photoassimilation of ¹⁴CO₂and retention of ^I4C, concomitant with significant decreasesin [¹⁴C]glycine and [¹⁴C]serine with increasing SO₂ concentration,implied that there was an inhibition of the photorespiratorypathway. At the second harvest, leaves from plants exposed to400 µg m– ³ SO₂ also exhibited significant increasesin [¹⁴C]sucrose and [¹⁴C]fructose.     

Absorption and Distribution of Copper in Plants with Sufficient or Deficient Supplies

Wheat, red clover and ryegrass were grown in flowing solutionculture with sufficient (+ Cu) and deficient (–Cu) suppliesof copper. The rates of Cu absorption (µg g^–1 dryroot day^–1) did not differ greatly between species ineither treatment. Wheat plants, when transferred from the –Cu to the +Cu treatment, absorbed Cu at a much slower rate thanthose which had remained throughout in the + Cu treatment. Inall plants considerable proportions of the absorbed Cu wereretained in the roots, even when the plants were Cu-deficient,and the concentration in roots usually exceeded that in anypart of the shoots in both treatments. Transferring wheat plantsfrom the +Cu to the –Cu treatment decreased the concentrationin all plant parts except old leaves; similarly, transferringfrom the –Cu to +Cu treatment increased the concentrationin all parts of the shoots, execept old leaves, and in the roots. Lolium perenne, Trifolium pratense, Triticum aestivum, ryegrass, red clover, wheat, absorption, copper, flowing solution culture     

Effect of Elevated CO2 on Stomatal Size and Distribution in Perennial Ryegrass

Plants of ryegrass (Lolium perenne L. cv. Melle) were grownfrom the early seedling stage in growth cabinets at a day/nighttemperature of 20/15 °C, with a 12-h photoperiod, and aCO₂ concentration of either 340 or 680 ± 15 µl1^–1 CO₂. Young, fully-expanded, acclimated leaves fromprimary branches were sampled for length of stomata, and ofepidermal cells between stomata, numbers of stomata and epidermalcells per unit length of stomatal row, numbers of stomatal rowsacross the leaf and numbers of stomatal rows between adjacentvein ridges. Elevated CO₂ had no significant effect on any ofthe measured parameters. Elevated CO₂, Lolium perenne, ryegrass, stomatal distribution, stomatal size     

Long-term Partitioning, Storage and Re-mobilization of 14C Assimilated by Lolium perenne (cv. Melle)

The youngest fully expanded leaves of single tillers of vegetativeperennial ryegrass plants were exposed to ¹⁴CO₂. Thereafter,quantitative and fractional analysis of the partitioning, storageand re-mobilization after defoliation of the ¹⁴C-labelled assimilatewas sequentially conducted over a 22 d period. In undefoliated plants, most ¹⁴C reached its final destinationwithin 5–6 of feeding. Forty per cent of assimilated ¹⁴Cwas subsequently lost through respiration, while 13.5, 8.5 and34 per cent remained in roots, stem bases and tops respectively.At least some ¹⁴C was distributed to tillers throughout theplant, but secondary tillers subtended by the fed tiller madethe greatest demand on ¹⁴C translocated from the fed tiller. A small, but significant portion of ¹⁴C was invested into longterm storage in undefoliated plants, four per cent of the totalassimilated still being present in a labile chemical form inroots and stem bases 22 d after feeding. In plants that wereseverely defoliated 4 d after feeding, depletion of reserve¹⁴C was observed relative to undefoliated plants. The depletiontook place from stem bases, not roots, and both low and highmolecular weight storage compounds were involved. A portionof the depleted ¹⁴C was incorporated into new growth after defoliation. Lolium perenne, perennial ryegrass, assimilate partitioning, storage, re-mobilization, defoliation     

A Comparison between the Uptake of Potassium by Plants from Solutions of Constant Potassium Concentration and during Depletion

A comparison was made between two methods of measuring the relationshipbetween the external [K⁺] and the flux of K⁺ into whole plantsof Lolium perenne and Raphanus sativus. The values of flux obtainedfrom solutions of 1.2 µM K⁺ held constant around the rootswere three and six times greater for Lolium and Raphanus respectivelythan the values obtained at the same concentration in a depletionexperiment in which the solutions, initially 100 µM K⁺,were depleted to below 1.2 µM K⁺ by plant uptake. In thedepletion experiment with Lolium, the flux was higher into plantsgrown at low [K⁺] than into plants grown at 100 µM eventhough [K⁺] within the plant was about the same for all groupsof plants. It is suggested that Lolium grown at low [K⁺] hasan efficient mechanism for K⁺ uptake which continues to operatefor some time after the plants have been transferred to a higherconcentration. With both species, K_m was 15–20 µMin the depletion experiment and below 1 µM when concentrationswere held constant.     

Effect of Cutting on Production and Tillering in Prairie Grass (Bromus willdenowii Kunth) Compared With Two Ryegrass (Lolium) species. 2. Reproductive Plants

Effects of time of initial cut and subsequent cutting interval(1, 2 or 4 weeks) were examined in a glasshouse during summer1988 for reproductive plants of three prairie grass cultivars(Bromus willdenowii Kunth), Westerwolds ryegrass (Lolium multiflorumLam.) and perennial ryegrass (Lolium perenne L.). Measurementswere made of tiller and leaf numbers, sites of tillering, reproductivedevelopment, and herbage quality and yields. Effect of timeof initial cutting on regrowth appeared to be independent ofstage of reproductive development and unrelated to any of themeasured plant parameters. Characteristics for each cultivaras identified during undisturbed growth prior to the initialcuts, were modified by the subsequent cutting frequencies. Perennial ryegrass had the highest yields under frequent cuttingwith high herbage quality. Westenwolds ryegrass and the prairiegrass cultivars ‘Grasslands Matua’ and ‘Primabel’had the highest yields with infrequent cutting, but lower herbagequality than in perennial ryegrass. At each cut, tiller deathin prairie grass was determined by the number of reproductivetillers, and in the ryegrasses also by the numbers of elongatedvegetative tillers. Recovery of tiller numbers was rapid andprimarily from inhibited tiller buds at the base of reproductivetillers. In prairie grass, tiller numbers were relatively unaffectedby cutting frequency, but at frequent cutting, many axillarytillers originated from vegetative tillers rather than frominhibited tiller buds at the base of reproductive tillers. Prairie grass, Bromus willdenowii Kunth, Westerwolds ryegrass, Lolium multiflorum Lam., perennial ryegrass, Lolium perenne L., first (initial) cut, cutting frequency, regrowth, leaf appearance, tillering, yield, nitrogen, water-soluble carbohydrates, herbage quality     

The Volatilization of Ammonia from Perennial Ryegrass During Decomposition, Drying and Induced Senescence

The volatilization of gaseous ammonia was measured from cutherbage (leaf lamina + sheath) of perennial ryegrass (Loliumperenne L.), during a 70 d period of either decomposition ordrying, and also from intact plants of perennial ryegrass subjectedto induced senescence by shading. Volatilization during decompositionamounted to 20–47% of the herbage nitrogen, but volatilizationduring drying, and from intact plants during induced senescence,amounted to less than 1% of the herbage nitrogen. During decomposition, volatilization of ammonia was proportionallygreater from herbage containing 3.52% nitrogen than from herbagecontaining 2.32% nitrogen. Volatilization occurred more rapidlyat 20 °C than at 10 °C but, with both samples of herbageand at both temperatures, at least 4 d elapsed before appreciablevolatilization occurred. Ammonia, atmosphere, decomposition, leaves, Lolium perenne L, nitrogen, perennial ryegrass     

Effect of Flowering on the Photosynthetic Capacity of Ryegrass Leaves Grown With and Without Natural Shading

The photosynthetic capacity of newly expanded leaves of vernalizedor non-vernalized plants of S24 perennial ryegrass (Lolium perenneL.), grown in long or short photoperiods, was measured in twoexperiments. In the first, leaves were protected from shadingduring development, while in the second, the natural shade ofneighbouring tillers in a sward was allowed. In the first experiment there was little effect of vernalization,day length or flowering, and leaves in all treatments had photosyntheticrates at 250 W m^–2 of between 28 and 32 mg CO₂ dm^–2h_–1.In the second experiment the photosynthetic rate of successiveleaves fell as sward leaf area increased. This downward trendwas reversed, however, in flowering tillers in the vernalizedlong-day treatment, while in the other treatments, which didnot flower, photosynthetic capacity continued to fall. It isconcluded that the leaves of reproductive tillers have highphotosynthetic capacities because stem extension carries themto the top of the canopy where they are well illuminated duringexpansion. Lolium perenneL, ryegrass, photosynthetic capacity, flowering, shading, vernalization     

Cyanobacteria and cyanobacterial toxins in three alkaline Rift Valley lakes of Kenya--Lakes Bogoria, Nakuru and Elmenteita

For decades frequent mass mortalities of Lesser Flamingos (Phoeniconaiasminor Geoffroy) have been observed at alkaline-saline KenyanRift Valley lakes. To estimate the potential influence of toxiccyanobacteria on these mass deaths, the phytoplankton communitieswere investigated in Lakes Bogoria, Nakuru and Elmenteita. Cyanobacterialtoxins were analyzed both in the phytoplankton from the threelakes and in isolated monocyanobacterial strains of Arthrospirafusiformis, Anabaenopsis abijatae, Spirulina subsalsa and Phormidiumterebriformis. Lake Bogoria was dominated by the cyanobacteriumA. fusiformis. In L. Nakuru and L. Elmenteita the phytoplanktonmainly consisted of A. fusiformis, A. abijatae and Anabaenopsisarnoldii, and in L. Nakuru an unknown Anabaena sp. was alsofound. Furthermore, this is the first time A. abijatae and theunknown Anabaena sp. have been found in Kenyan lakes. Phytoplanktonwet weight biomass was found to be high, reaching 777 mg L^–1in L. Bogoria, 104 mg L^–1 in L. Nakuru and 202 mg L^–1in L. Elmenteita. Using HPLC, the cyanobacterial hepatotoxinsmicrocystin-LR, -RR -YR, -LF and -LA and the neurotoxin anatoxin-awere detected in phytoplankton samples from L. Bogoria and L.Nakuru. Total microcystin concentrations amounted to 155 µgmicrocystin-LR equivalents g^–1 DW in L. Bogoria, and 4593µg microcystin-LR equivalents g^–1 DW in L. Nakuru,with anatoxin-a concentrations at 9 µg g^–1 DW inL. Bogoria and 223 µg g^–1 DW in L. Nakuru. In L.Elmenteita phytoplankton, no cyanobacterial toxins were found.A. fusiformis was identified as one source of the toxins. Theisolated strain of A. fusiformis from L. Bogoria was found toproduce both microcystin-YR (15.0 µg g^–1 DW) andanatoxin-a (10.4 µg g^–1 DW), whilst the A. fusiformisstrain from L. Nakuru was found to produce anatoxin-a (0.14µg g^–1 DW). Since A. fusiformis mass developmentsare characteristic of alkaline-saline lakes, health risks towildlife, especially the Arthrospira-consuming Lesser Flamingo,may be expected.     

Nitrate Effects on Growth of the First Four Main Stem Leaves of a Range of Temperate Cereals and Pasture Grasses

The effects of different applied NO₃^– concentrations onextension growth and final length and area of leaves 1–4of five cereals and six pasture grasses of temperate originwere examined. Increased applied NO₃^– in the range 0.1–0.5.0mol m^–3 caused decreased duration of growth but increasedgrowth rate and final length of leaves 2–4 of the cerealsAvena saliva, Hordeum vulgare, Secale cereale, x Triticosecaleand Triticum aestivum. For all cereals, increased NO₃^–resulted in increased area of leaves 1–4. Pasture grasseswere supplied either 0.5 or 50 mol m^–3 NO₃^–. Increasedapplied NO₃^– (0.5–5.0 mol m^–3) resulted indecreased duration of growth and increased growth rate and finalarea of leaves 1–4 of Bromus wiltdenowii, leaves 2–4ofFestuca arundinaceae and leaves 3 and 4 of Lolium muitiflorum.In addition, length of leaves 3 and 4 of B. witidenowii increasedwith increased NO₃^–. Increased NO₃^– resulted inincreased area of leaves 2–4 of Dactylis gtomerata andLolium perenne and leaves 3 and 4 of Phalaris aquaiica but hadno effect on extension growth of all three species. Avena sativa L, oat, Hordeum vulgare L, barley, Secale cereale L, rye, x Triticosecale Wittm, triticale, Triticum aestivum L, wheat, Bromus willdenowii Kunth, prairie grass, Dactylis gtomerata L, cocksfoot, Festuca arundinaceae Shreb, tall fescue, Lolium multijlorum Lam, Italian ryegrass, Lolium perenne L, perennial ryegrass, Phalaris aquatica L, nitrate, leaf extension, leaf expansion     

The Uptake of Phosphate by Plants from Flowing Nutrient Solution: III. EFFECT OF CHANGED PHOSPHATE CONCENTRATIONS ON THE GROWTH AND DISTRIBUTION OF PHOSPHATE WITHIN PLANTS OF LOLIUM PERENNE L.

Perennial ryegrass (Lolium perenne L.) was grown from seed for29 d in flowing solution culture containing 0.1, 0.4 or 6.4mmol m^–3 P before the concentrations were changed (0.1and 0.4 raised to 6.4; 6.4 lowered to 0.4; controls unchanged)for an experimental period of two weeks to test the hypothesisthat after the seedling stage, the maximum rate of plant growthcould be sustained by a lower concentration of phosphate atthe root/solution interface than was necessary for the maximumrate of seedling growth. During the 29 d seedling period growthwas greatest on 6.4 mmol m^–3 P achieving 179 mg per plantdry weight compared with 122 and 26 mg on 0.4 and 0.1 mmol m^–3P respectively. During the experimental period growth on thetreatment 6.4 lowered to 0.4 mmol m^–3 P continued at thesame rate as the 6.4 control achieving 981 and 983 mg per plantdry weight respectively. Similarly growth of the treatment 0.4raised to 6.4 mol m^–3 P was unaffected by the change inconcentration and was comparable with the 0.4 control. Bothresults support the hypothesis for seedlings exceeding about100 mg per plant dry weight. In contrast the small plants ofthe treatment 0.1 raised to 6.4 mmol m^–3 P behaved similarlyto seedlings and responded rapidly to the increased concentrationof phosphate in solution, achieving high rates of phosphateuptake and increasing the growth of shoot more than the growthof root so that the ratio of root: shoot declined from 065 to0.34, a value similar to that for the seedlings grown on 6.4mmol m^–3 P. Key words: Lolium perenne L, Phosphate concentration, Seedling growth     

The Uptake of Phosphate by Plants from Flowing Nutrient Solution: I. CONTROL OF PHOSPHATE CONCENTRATION IN SOLUTION

An existing system of flowing solution culture in which pH andthe concentration of several nutrient ions in solution are automaticallymonitored and controlled has been extended to include the monitoringand control of orthophosphate in the range 0.0013 to 0.3 mgP l^–1 (4.2 ? 10^–8–10^–5 M). Continuous-flowcolorimetry is used for the analysis of phosphate and a computeris employed to hold concentrations constant by the operationof nutrient pumps. A brief account is given of the performanceof the system with perennial ryegrass (Lolium perenne L.) asthe experimental plant.