Hardening and Dehardening of Lolium perenne in Response to Fluctuating Temperatures

Hardening and dehardening responses of two contrasting varietiesof Lolium perenne, measured as LT50 estimates, were followedin fluctuating temperature environments. Unhardened seedlingswere exposed to hardening environments for 7, 14, and 21 d inall combinations of 2, 4, 6, 8 and 10 C with either high dayand low night temperatures or low day and high night temperatures.Seedlings hardened for 28 d at 2 C were exposed to dehardeningenvironments in all combinations of 4, 6, 8, 10, and 12 C withhigh day and low night temperatures. A low day, or night, temperature of 2 C in combination withany other temperature increased hardening compared with theconstant higher temperature. For Premo, a hardy variety, thisincrease was 3 C when night temperature was reduced from 10to 2 C in combination with a day temperature of 10 C. Similarly,a low night temperature reduced the dehardening response ofPremo to higher day temperatures. At 12 C this effect on LT60was greater than 2 C. Much smaller responses to daily periodsof low temperature were found for the less hardy variety, GrasslandsRuanui. During each 24-h period, exposures to 2 C of longer than 4h were required to achieve greater hardening than that achievedin continuous 10 C treatments. Hardiness was not improved furtherby exposures longer than 8 h. Responses to diurnal temperature fluctuations were discussedin relation to possible mechanisms and to changes in hardinessduring the winter under different weather systems. Lolium perenne, cold hardening, cold dehardening, diurnal temperature fluctuations, varieties     

Application of Impedance Spectroscopy for Selecting Frost Hardy Varieties of English Ryegrass

The frost hardening and frost damage of 12 varieties of Englishryegrass (Lolium perenne) was studied by electrical impedancespectroscopy. For the measurement of the impedance spectrum(80 Hz to 1 MHz) a 10 mm length sample was cut from the stemabove the growing point, but the growing point was included.The impedance spectra were analysed by an asymmetric distributedcircuit model. The impedance spectra were measured at two phasesof hardiness and after freezing, i.e. (a) before hardening,(b) after hardening in controlled conditions, and (c) aftercontrolled frost exposure at -16 °C after hardening. Twomodel parameters, i.e. intra- and extracellular resistance,increased with hardening. The intracellular resistance and theskewness factor before hardening, and the ratio between thosetwo parameters before and after hardening, strongly correlatedwith hardening of different varieties of English ryegrass. Theextracellular resistance and the relaxation time decreased asa result of the frost exposure at -16 °C. Cold acclimation; electrical impedance; English ryegrass; frost hardiness; impedance spectroscopy; Lolium perenne     

A Second-order Dynamic Model for the Frost Hardiness of Trees

The development of frost hardiness in forest trees is describedby a dynamic model in which the input variables are the prevailingenvironmental conditions and the developmental stage of trees.The assumption of the model is that for each temperature andphotoperiod there is a discrete stationary level of frost hardiness,which is attained if these environmental factors remain constant.The dependence of the stationary level on temperature and photoperiodis assumed to be piece-wise linear and additive. The rate ofacclimation, i.e. frost hardening or dehardening, is describedas a second-order dynamic process with two time constants, thesecond of which changes depending on the stage of the annualdevelopment of the trees. The frost hardiness model was calibratedand tested using experimental data from Douglas fir [Pseudotsugamenziesii var. glauca (Beissn.) Franco] seedlings. The resultssuggest that the second-order model describes the changes infrost hardiness better than the first-order model with onlyone time constant.Copyright 1995, 1999 Academic Press Acclimation, developmental stage, Douglas fir, dynamic model, frost hardiness, photoperiod, Pseudotsuga menziesii, temperature     

Short-day and Low-temperature Induction in Lolium

The requirements for floral induction of several outbreedingpopulations of Lolium perenne, L. multiflorum, and L. rigidumhave been studied. Floral induction can be brought about byeither low temperature (0–30° C.) or short day (8hr.) independently, but short day is ineffective at low temperatures. The exact inductive requirement varies with the population.The summerannual Westerwolds ryegrass needs neither cold norshort day, the winter-annual Wimmera ryegrass shows a quantitativeresponse, while the perennial varieties from north-west Europehave an obligatory requirement for either cold or short daybefore floral induction. This relation between the annual orperennial habit and the inductive requirement was confirmedin a number of Mediterranean collections of L. perenne and L.rigidum. Considerable genetic variation in inductive requirement couldbe detected within each outbreeding population, and rapid responseto selection proved possible in Wimmera, Irish, and Kent ryegrass.     

Changing Environmental Effects on Frost Hardiness of Scots Pine During Dehardening

The effects of raised temperature and extended photoperiod onthe dehardening of quiescent and winter-hardy Scots pine saplingswere examined in an open-top-chamber experiment. The saplingswere exposed during winter to natural, square-curve fluctuating(between 1 and 11 °C with a 14 d interval), and constant(6 °C) temperatures with a natural and an extended (17 h)photoperiod. Frost hardiness of needles was determined by controlledfreezing tests and visual damage scoring. The constant 6 °Ctemperature treatment caused a gradual dehardening of needleswhereas under fluctuating temperatures the level of frost hardinessfluctuated. Trees exposed to extended photoperiods were lesshardy than under natural photoperiods after the initiation ofshoot elongation, but before this there were no clear differencesin frost hardiness between different photoperiodic treatments.The results indicate that the frost hardening competence ofScots pine changes during quiescence. Climate change; frost hardiness; hardening competence; photoperiod; Pinus sylvestris, Scots pine; temperature     

The Effect of Sulphur Dioxide on the Growth of Lolium perenne L., Lolium multiflorum Lam., Dactylis glomerata L., and Phleum pratense L.

Lockyer, D. R. 1985. The effect of sulphur dioxide on the growthof Lolium perenne L., Lolium multiflorum Lam., Dactylis glomerataL., and Phleum pratense L.?J. exp. Bot. 36: 1851-1859. Fouragriculturally important grasses, Lolium perenne L., Loliummultiflorum Lam., Dactylis glomerata L. and Phleum pratenseL. were exposed to sulphur dioxide (SO₂) in a system of exposurechambers. The plants were exposed for a total of 43 d to meanconcentrations of SO₂ in the air of 0,87 or 448 (µg m^–3and herbage was harvested twice. All four grasses showed chloroticlesions after exposure to the highest concentration of SO₂.The effect of SO₂ on the yield of herbage was statisticallysignificant only at the second harvest and at the highest concentration;the dry weights of shoots of D. glomerata and L. perenne werereduced by 33% and 16% respectively. Significant effects ofSO₂ were also found on the 'transpiration coefficients' measuredfor D. glomerata and P. pratense. The grasses differed in theiruptake of sulphur from the atmosphere but this was not relatedto their sensitivity to SO₂. Total–S concentration inthe shoots of L. perenne, L. multiflorum and D. glomerata increasedalmost linearly in response to increasing SO₂ concentration;with P. pratense only the highest SO₂ concentration raised total-Sabove the level in control plants. These increases were almostentirely due to the accumulation of sulphate–S. Key words: Sulphur diozide, Lolium perenne, Lolium multiflorum, Dactylis glomerata, Phleum pratense     

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     

Analysis of Variation in Growth Habit of Lolium Populations

Genetic variation in growth habit between six contrasting populationsof Lolium perenne and L. multiflorum is analysed by means ofa complete diallel grown in three seasonal environments. Themain population differences are between the more erect biennialforms of L. multiflorum and the prostrate perennial forms ofL. perenne. It is suggested that these differences are attributableto past agronomic (biotic), rather than climatic, selectionpressure. In winter all six parental populations are more erectthan in spring or summer, although interaction between populationsand environments does occur. The genetic control of the populationdifferences is due to average zygotic effects but both constantand residual reciprocal effects of the parent also determinethe performance of the F₁ crosses over the three environments.Reciprocal effects are constant over environments, whereas averagezygotic effects interact with environments.     

Photosynthesis and Photorespiration in Lolium multiflorum and Lolium perenne

The response of net photosynthesis to changing light-flux densityby leaves of Lolium multiflorum (S. 22) and L. perenne (S. 321)is more adequately described by current models when a term allowingfor photorespiration is included. The magnitude of this termwas determined from the changes in the slope of the light-responsecurves for net photosynthesis. A pseudo first-order rate-constantfor photorespiration, and a pseudo second-order rate-constantfor photosynthesis calculated by this technique for L. multiflorumwere found to be similar to corresponding parameters calculatedfrom light-compensation-point measurements using a simple modeldescribed by Brown (1969). The relative magnitudes of respirationand photosynthesis at light saturation for both Lolium specieswere similar to reported values for other temperate species(Lake, 1967). Two selection lines of L. perenne (S. 321) with contrastingdry-matter yields were found to have the same parameters forrespiration and photosynthesis.     

Effect of Cutting on Production and Tillering in Prairie Grass (Bromus willdenowii Kunth) Compared With Two Ryegrass (Loliunt) Species. 1. Vegetative Plants

Effects of cutting to 3 or 6 cm stubble height at frequenciesof 1, 2 or 4 weeks were investigated in young, vegetative, spacedplants of prairie grass (Bromus willdenowii Kunth), a tetraploidWesterwolds ryegrass (Lolium multiflorum Lam.) and perennialryegrass (Lolium perenne L.). Plants were grown for 8 weekson nutrient solution in a growth cabinet at day/night temperaturesof 15/10°C and in a short photoperiod. Leaf appearance,site filling and tiller numbers were all reduced by both increasedcutting frequency and a lower cutting height. The extent ofthese reductions was least in prairie grass and greatest inWesterwolds ryegrass. Relative growth rates in all species respondedin a similar manner with more frequent cutting and a lower cuttingheight. Cutting frequency had the greatest effect on growthrates, although the effect of cutting height increased withtime. Results confirm general recommendations of long intervalsbetween defoliations to achieve high yields for vegetative prairiegrass, but the relative amounts of dry matter harvested underthe different cutting regimes may be no different to that obtainedin ryegrass. Stubble height was of lesser importance in determiningyields. A typical U-shaped curve for depletion and recovery in water-solublecarbohydrates occurred after defoliation in all species, butlevels remained low at frequent cutting. Water-soluble carbohydratelevels in stubble and roots were higher in prairie grass. Regrowthat the end of the experiment was highly correlated with totalstubble and root weights (r = 0.84), while regrowth per tillershowed a good correlation with water-soluble carbohydrate content,although the response varied between species. Prairie grass, Bromus willdenowii Kunth, perennial ryegrass, Lolium perenne L., Westerwolds ryegrass, Lolium multiflorum Lam., cutting frequency, cutting height, leaf appearance, tillering, site filling, yield, regrowth, nitrogen, water-soluble carbohydrates     

Amino acid changes associated with low temperature treatment of Lolium Perenne

Exposure of Lolium perenne to conditions which favour the development of cold hardiness resulted in an accumulation in the leaves of proline, serine, glycine, glutamic acid and glutamine.     

Water Use Characteristics of Dactylis glomerata L., Lolium perenne L. and L. multiflorum Lam. Plants

Cocksfoot (Dactylis glomerata L.). perennial ryegrass (Loliumperenne L.) and Italian ryegrass (L. multiflorum Lam.) plantswere grown on deep (75–95 cm) columns of soil in glasshousesand growth rooms with and without irrigation. The species inwhich growth declined least rapidly after water had been withheldwere those which transpired most slowly. During early establishmentin the glasshouse cocksfoot transpired least because of slowroot growth. In the growth room, when root systems were deeperand denser, perennial ryegrass transpired least because of lowleaf water conductance. Results are discussed in relation to(a) drought resistance in the three species; (b) breeding forincreased drought resistance through modifying root distributionand leaf water conductance; and (c) the use of isolated soilcolumns in water relations studies. Dactylis glomerata L., Lolium perenne L., Lolium multiflorum Lam., cocksfoot, perennial ryegrass, Italian ryegrass, transpiration, roots, leaf water conductance     

Frost tolerance and biochemical changes during hardening and dehardening in contrasting white clover populations

Successful winter survival of perennial plants, like white clover, is dependent on proper timing of both hardening and dehardening. The purpose of this study was to investigate the regulation of these processes in two cultivars (AberCrest and AberHerald) and two Norwegian ecotypes (Særheim collected at 58°46′N lat. and Bodø at 67°20′N lat.) of white clover (Trifolium repens L.). For hardening and dehardening, plants were exposed to controlled temperature conditions and frost hardiness of stolons was tested by programmed freezing at the rate of 3°C per hour. In addition, stolons were analysed for starch, soluble sugars and soluble amino acids. Cultivars AberCrest and AberHerald, selected for growth at low temperature and winter hardiness in the United Kingdom, were significantly less hardy than the Norwegian populations. After six weeks of hardening (2 weeks at 6°C and 4 weeks at 0.5°C), estimated LT₅₀ values were ?13.8, ?13.0, ?17.8 and ?20.3°C for AberCrest, AberHerald, Saerheim and Bodø, respectively. The rate of dehardening increased with increasing temperature. At low temperature (6°C), the northern ecotype from Bodø was more resistant to dehardening than AberHerald. However, at 18°C the absolute rate of dehardening (°C day^?1) was twice as high in Bodø as in AberHerald plants. Stolon elongation during dehardening was initiated at lower temperatures in AberHerald than in plants of the Bodø ecotype. The content of total soluble sugars, sucrose and the amino acids proline and arginine were significantly higher in hardy plants of Bodø than in those of AberHerald. Sucrose levels decreased during dehardening and correlations between sucrose content and LT₅₀ during this process were statistically highly significant for both Bodø and AberHerald. The least hardy populations of white clover were characterized by thick stolons, long internodes and large leaves.     

Microclimate, Canopy Structure and Photosynthesis in Canopies of Three Contrasting Temperate Forage Grasses: II. Microclimate and Canopy Structure

Profiles of shortwave radiation, net radiation and temperaturewere measured in swards of three grasses of contrasting structureLolium perenne cv. S24, L. perenne cv. Reveille and Festucaarundinacea cv. S170. Measurements were also made of the reflectionof shortwave radiation, leaf water potential and stomatal resistance.Differences in canopy structure influenced the absorption andreflection of radiation by the varieties. The absorption ofnet radiation and its influence on air temperature inside thecanopy was shown to vary with canopy structure. Calculationsshowed that diurnal changes in the reflection and transmissionof light (400–700 nm) would have little effect on canopyphotosynthesis. No clear relationship between leaf extensionrate, temperature and leaf water potential could be established,although decreases in water potential did appear to reduce thepotential response of leaf extension rate to temperature.     

Assimilation Rate and Growth of Lolium Populations in the Glasshouse in Contrasting Light Intensities

Using growth-analysis techniques, the variation in relativegrowth-rate (RGR) and its components, net assimilation rate(NAR), and leaf-area ratio (LAR), was examined in 18 populationsof L. perenne, six of L. multiflorum, and two hybrid cultivarsfrom contrasting climatic and agronomic origins, grown at lowand high light intensities in the glasshouse. Significant differences between populations were found for RGR,NAR, and LAR at both light intensities. At both intensitiesthe annual or biennial multiflorum group had a greater LAR anda lower specific leaf weight and chlorophyll content than theperennial perenne group. At the low intensity this was compensatedby a greater NAR in the perenne group, with no resultant differencein RGR. At the high intensity there was no difference betweenthe groups in NAR, and hence a greater RGR in the multiflorumgroup. Within the perenne and multiflorum groups, at both light intensities,the variation between populations in RGR was based on differencesin NAR rather than in LAR. There was no regular correlationof NAR with either specific leaf weight, or chlorophyll contentat either light intensity, though at low light intensity itwas significantly correlated with shoot-root ratio.     

Changes in Dry Matter, Carbohydrate and Seed Yield Resulting from Lodging in Three Temperate Grass Species

The adverse effect of lodging on grass seed yield may be attributed,in part, to assimilate limitation during the seed filling period.This investigation examined plant dry matter assimilate partitioningand seed yield as affected by lodging in three species thatare closely related but phenotypically different: tall fescue(Festuca arundinacea Schreber.), Italian ryegrass (Lolium multiflorumLam.), and perennial ryegrass (L. perenne L.). Studies wereperformed in field plots at Corvallis, Oregon, USA. Seed yieldcomponents (seed number per inflorescence, seed yield per inflorescence,and single seed mass) and leaf, stem (lower, middle, and peduncle)and seed inflorescence dry mass were measured just prior toanthesis to seed maturity. Dry mass and water soluble carbohydrates(WSC) were determined for shoot components. The reduction indry mass and WSC in leaves and stem components following anthesiswas often greater in lodged plants compared to upright plants.The relatively low seed yield depression in lodged tall fescuesuggested a higher compensation potential for partitioning reserveassimilate from leaves and stems to support seed growth anddevelopment. This potential does not appear to be present tothe same degree in Italian ryegrass and to an even lesser extentin perennial ryegrass. These findings suggest that the potentialto compensate for reduced assimilate supply during the periodof high assimilate demand by seeds may be attributed, in part,to the total assimilate reserve accumulated prior to photoassimilatereduction caused by the lodged condition. Copyright 2000 Annalsof Botany Company Tall fescue, Festuca arundinacea Schreber., Italian ryegrass, Lolium multiflorum Lam., perennial ryegrass, L. perenne L., assimilate partitioning, source–sink     

Effects of Hormones on Morphogenesis and Cold Resistance in Berseem Clover (Trifolium alexandrinum L.)

Plants of berseem clover (Trifolium alexandrinum L.) cv. Taborwere raised under conditions inhibiting the acquisition of coldhardiness (non-hardened) or inducing cold hardiness (hardened).All non-hardened plants developed an elongated shoot and exhibitedconsiderable frost sensitivity, as measured by the extent ofthe reduction in yield of variable chlorophyll fluorescenceafter exposure to sub-zero temperature. Hardened plants developeda shorter shoot, with fewer leaves and a greater percentageof dry matter in the root system. These parameters were associatedwith a marked increase in frost resistance. Exogenous applicationof ABA to plants effected similar morphological modificationsin both hardening and non-hardening temperature regimes; plantsdeveloped a shorter primary shoot axis and leaves exhibiteda marked increase in frost hardiness. In berseem clover ABAcan thus substitute, at least partially, for the low temperaturetreatment required to induce cold hardiness. Spraying plantsraised under hardening conditions with gibberellic acid reversedthe effects of the hardening treatment, since they developedan elongated shoot and exhibited frost sensitivity comparableto non-treated plants grown under non-hardening conditions.It is concluded that these endogenous hormones are directlyinvolved in triggering changes in morphogenesis which accompanyphysiological and metabolic events associated with the inductionof plant cold hardiness. Key words: Frost resistance, morphogenesis, abscisic acid, giberellic acid, Trifolium alexandrinum     

A Comparison of the Morphology and Anatomy of Seedling Leaves of Lolium multiflorum Lam. and L. perenne L.

A rapid technique has been developed for studying the morphologyand anatomy of leaves of forage grasses. It has been used tocompare the leaf dimensions, numbers of structural elements,tissue proportions, stomatal and unicellular hair counts, andmesophyll cell number and size in one variety of Lolium multiflorumLam. and L. perenne L. There were large differences betweenthese species in leaf dimensions, number of structural elements,and in stomatal and unicellular hair counts, but little differencein the relative proportion of different tissues and in cellsize.     

Photoperiod control of the initial phase of frost hardiness development in Pinus radiata

Abstract. The development of frost hardiness in Pinus radiata was investigated to establish whether there is quantitative relationship between photoperiod and the hardening process. Three controlled environment experiments were carried out. In the first, seedlings were exposed to a photoperiod that shortened from 13 h at a rate of 3 min d^?1 to 9.5 h. At intervals, the photoperiod was either held constant or lengthened. In the second experiment, seedlings were exposed to one of five constant photoperiods between 9 and 12 h for up to 90 d. In the third, seedlings were exposed to photoperiods shortening at rates of 1 or 5 min d^?1. Frost hardiness was also measured during the natural photoperiod-controlled stage of hardening in outdoor-grown seedlings. Frost hardiness developed at a constant rate in response to a shortening photoperiod once it had declined to about 12 h. This rate was consistent with the hardening rate that occurred in outdoor-grown seedlings. Hardening stopped when the photoperiod became constant, indicating a tight coupling between changes in photoperiod and hardiness development. When the photoperiod was held constant, the extent of frost hardiness was directly dependent on the photoperiod but the rate of hardening was apparently independent of the length of photoperiod. However, the rate of hardening was dependent on the rate at which the photoperiod shortened, increasing linearly with increases in the rate of change in photoperiod between 0 and 3 min d^?1. These results suggest shortening photoperiods control the first stage of the hardening process by regulating the rate of hardening. Frost hardening was inherently unstable once the maximum hardiness was reached since spontaneous dehardening occurred in spite of the controlled conditions. Dehardening also occurred when the photoperiod was lengthened suggesting that the cue for dehardening to commence was the shift from shortening to lengthening photoperiods.     

Leaf Photosynthetic Activity in Six Temperate Grass Varieties Grown in Contrasting Light and Temperature Environments

Three populations of each of Lolium perenne and Lolium multiflorumwere grown at four temperatures at each of three light intensities.Concurrent studies were made on the response of leaf photosyntheticactivity and leaf structure of newly-expanded leaves of 7-weekold seedlings of each of the populations to the contrastinggrowth environments. Photochemical efficiencies, leaf conductances, photorespirationconstants and apparent activation energies for photosynthesiswere calculated for each population in each of the twelve growthenvironments. Photosynthetic rates at light saturation were expressed on thebasis of leaf area, of leaf volume and of leaf mesophyll tissuevolume. Photosynthetic rates were also measured under differentassay conditions. By expressing photosynthetic rates on a leaf volume basis, variationbetween populations and growth environments resulting from leafstructural changes were partially removed.