The Effect of Light Quality on Shoot Extension Growth in Three Species of Grasses

The effect of light quality on the extension growth of vegetativeshoots and on the final size of their leaves was investigatedin plants of Lolium multiflorum, Sporobolus indicus and Paspalumdilatatum. Three experimental approaches were used, (a) redor far-red end-of-day irradiations of sunlight-grown plants,(b) different red/far-red ratios of white light in a growthroom and (c) sunlight enrichment with radiation of differentred/far-red ratios or with different amounts of far-red lightduring the photoperiod. Plants treated with end-of-day far-redor low red/far-red ratios throughout the photoperiod developedlonger leaves and, as a result, longer shoots. This effect wasmore marked in leaf sheaths than in blades. Tiller extensionand leaf sheath length increased with the amount of far-redadded to sunlight in a simple hyperbolic relationship. Theseresults show that vegetative grass shoots respond to light qualityin a way similar to internodes of dicotyledonous plants. Lolium multiflorum Lam., Sporobolus indicus (L.), Paspalum dilatatum (Poir.), leaf growth, tiller growth, photomorphogenesis     

Effects of CO2 enrichment and intraspecific competition on biomass partitioning, nitrogen content and microbial biomass carbon in soil of perennial ryegrass and white clover

Seedlings of perennial ryegrass (Lolium perenne L. cv. Parcour)and white clover (Trifolium repens L. cv. Karina) grown at fivedifferent plant densities were exposed to ambient (390 ppm)and elevated (690 ppm) CO₂ concentrations. After 43 d the effectsof CO₂ enrichment and plant density on growth of shoot and root,nitrogen concentration of tissue, and microbial biomass carbon(C_mic) in soil were determined. CO₂ enrichment of Lolium perenneincreased shoot growth on average by 17% independent of plantdensity, while effects on root biomass ranged between -4% and+ 107% due to an interaction with plant density. Since tilernumber per plant was unaffected by elevated CO₂, the small responseof shoot growth to CO₂ enrichment was atributed to low sinkstrength. A significant correlation between nitrogen concentrationof total plant biomass and root fraction of total plant drymatter, which was not changed by CO₂ enrichment, indicates thatnitrogen status of the plant controls biomass partitioning andthe effect of CO₂ enrichment on root growth. Effects of elevatedCO₂ and plant density on shoot and root growth of Trifoliumrepens were not significantly interacting and mean CO₂-relatedincrease amounted to 29% and 66%, respectively. However, growthenhancement due to elevated CO₂ was strongest when leaf areaindex was lowest. Total amounts of nitrogen in shoots and rootswere bigger at 690 ppm than at 390 ppm CO₂. There was a significantincrease in C_mic in experiments with both species whereas plantdensity had no substantial effect. Key words: CO₂ enrichment, intraspecific competition, biomass partitioning, Lolium perenne, Trifolium repens, grassland     

Yield-Respiration Relationships at Different Bean (Phaseolus vulgaris) Plant Densities

Bean (Phaseolus vulgaris L.) plants were grown, one to fiveplants per pot, with a non-limiting supply of mineral nutrients.As plant density increased, seed and N yield per plant decreased,but those per pot remained fairly constant. The shoot: rootratio and the contribution of roots to total plant respirationwere also almost constant with changing density; the Q₁₀ forshoot respiration was higher at maximal densities. However,growth respiratory C losses per plant over the growth periodon a seed dry matter of N yield basis were not dependent onplant densities tested. Phaseolus vulgaris L., yield, respiration, plant density     

Variations in Tiller Dynamics and Morphology in Lolium multiflorum Lam.Vegetative and Reproductive Plants as affected by Differences in Red/Far-Red Irradiation

Lolium multiflorum Lam, plants were grown in a growth room undertwo light sources with red/far-red ratios of 1·62 and0·84 but similar photosynthetically active radiation.In both situations the capacity to produce new tillers and thelight available per tiller decreased with canopy growth. Tilleringwas further reduced by the low red/far-red ratio while lightinterception and plant dry weight were unaffected by this treatment.In both reproductive and vegetative plants under the lower red/far-redratio the time between leaf expansion and the appearance ofa tiller in its axil was increased and the proportion of ‘maturebuds’ that developed was reduced. Irradiation with lowred/far-red advanced the reproductive development and increasedthe number of fertile tillers per plant. It also caused longerleaf sheaths, blades and reproductive shoots. The results suggestthat as canopy density increases the lower light interceptionper tiller and the photomorphogenic effect of low red/far-redratios may reduce the capacity to produce new tillers. Lolium multiflorum, Lam., annual ryegrass, tillering, tiller growth, leaf growth, flowering, light quality.     

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     

The Distribution of Assimilates in Lolium multiflorum Lam. Following Differential Defoliation

In seedling plants of Lolium multiflorum Lam. the tillers weredefoliated but the main shoot was left intact. Radiocarbon as¹⁴CO₂ was supplied to this shoot at different times followingtiller defoliation and the pattern of distribution of labelledassimilates was determined quantitatively. It was found thata greater proportion (approximately 10–20 per cent) ofexported assimilate was translocated to the cut tillers butalthough the proportion supplied to the root system was lessthe total radiocarbon incorporated by the roots was unchanged.This was brought about by a large increase in the export ofradiocarbon fixed by the intact shoot—up to 100 per centfollowing one treatment. These alterations in the organizationof the defoliated plant lead to a greater efficiency in thecarbon economy and are discussed in relation to the stress imposedby defoliation.     

Variation in Photorespiration in Lolium

The rate of photorespiration in several grass species was shownto be highly variable and dependent on the species, genotype,and conditions under which the plants were grown. Photorespiration,measured as oxygen uptake, was negligible in Cenchrus ciliarisand Paspalum dilatatum but significant in Lolium spp. and Festucaarundinacea. There were significant differences in the rateof photorespiration among plants within a Lolium populationof diverse origin and these differences were independent ofthe conditions under which the plants were grown. Among thetemperate grasses there was a significant correlation betweenphotorespiration and the CO₂-compensation concentration andboth parameters were very low in P. dilatatum. Plants grownin day/night temperatures of 15/10 °C compared with 25/20°C had faster rates of dark respiration but slower ratesof light respiration when measured at the same temperature.Photorespiration was faster than dark respiration although differencesin respiration among plants in the light were not shown in thedark.     

Effects of Flooding and Drought on the Anatomy of Paspalum dilatatum

Paspalum dilatatum occupies different topographic positionsin the Flooding Pampa, Argentina. Populations from differentpositions are subjected to various regimes of flooding and drought,both of which may occur in the same growing season. We investigatedthe constitutive and plastic anatomical traits of P. dilatatumpopulations from habitats with contrasting regimes of floodingand drought. Both events affected root and sheath anatomy, andthese effects were similar for clones from different topographicpositions. Flooding increased the aerenchymatous tissue in theroot cortex and the leaf sheaths and decreased the number ofroot hairs per unit of root length. Drought decreased the diameterof root metaxylem vessels, thus lowering the risk of embolismsand increasing water-flow resistance, and increased the numberof root hairs, thereby increasing water uptake ability. In additionto these plastic responses, all clones showed constitutive characteristicsthat may confer an ability to withstand sudden events of floodingor drought: a high proportion of aerenchyma, which may maintainaeration before plastic responses take place; sclerenchyma,which may prevent root and leaf sheath collapse by soil compaction;and a conspicuous endodermis, which may protect stelar tissuesfrom desiccation. Both constitutive and plastic anatomical characteristicsare likely to contribute to the ability of this species to occupywidely different topographic positions and to resist temporalvariations in water and oxygen availability. Copyright 2001Annals of Botany Company Flooding, drought, aerenchyma, vessels, roots, leaf sheaths, anatomy, Paspalum dilatatum Poir     

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.     

Grazing history effects on above- and below-ground litter decomposition and nutrient cycling in two co-occurring grasses

Large herbivores may alter carbon and nutrient cycling in soil by changing above- and below-ground litter decomposition dynamics. Grazing effects may reflect changes in plant allocation patterns, and thus litter quality, or the site conditions for decomposition, but the relative roles of these broad mechanisms have rarely been tested. We examined plant and soil mediated effects of grazing history on litter mass loss and nutrient release in two grazing-tolerant grasses, Lolium multiflorum and Paspalum dilatatum, in a humid pampa grassland, Argentina. Shoot and root litters produced in a common garden by conspecific plants collected from grazed and ungrazed sites were incubated under both grazing conditions. We found that grazing history effects on litter decomposition were stronger for shoot than for root material. Root mass loss was neither affected by litter origin nor incubation site, although roots from the grazed origin immobilised more nutrients. Plants from the grazed site produced shoots with higher cell soluble contents and lower lignin:N ratios. Grazing effects mediated by shoot litter origin depended on the species, and were less apparent than incubation site effects. Lolium shoots from the grazed site decomposed and released nutrients faster, whereas Paspalum shoots from the grazed site retained more nutrient than their respective counterparts from the ungrazed site. Such divergent, species-specific dynamics did not translate into consistent differences in soil mineral N beneath decomposing litters. Indeed, shoot mass loss and nutrient release were generally faster in the grazed grassland, where soil N availability was higher. Our results show that grazing influenced nutrient cycling by modifying litter breakdown within species as well as the soil environment for decomposition. They also indicate that grazing effects on decomposition are likely to involve aerial litter pools rather than the more recalcitrant root compartment.     

A Method for in Vitro Storage of Lolium multiflorum Lam

A means of storing Lolium multiflorum Lam. stock plants in vitrohas been developed over a period of three years. Variousexplantsand cultureconditions were examined. Shoot tips 0.3–0.9mm long were found to be best for establishing storage culturesbecause they gave a high yield of plantlets in culture and importantpathogens are eliminated. For sub-culturing, after each annualcycle of storage at 2–4 °C, shoot tips, tiller buds,tiller bases and nodes can be used. Tiller buds were most abundantand best for increasing the number of stored plantlets whennecessary. There was no advantage of including an auxin in theculture medium for shoot tips and Murashige and Skoog's mediumwith 0.2 mg l^–1 kinetin has been adopted for initiating,sub-culturing and storing cultures. The optimum temperaturerange for regenerating plantlets was 20–25 °C. Lightwas necessary for a high rate of plantlet regeneration and lightquality and intensity affected their growth. Lolium multiflorum Lam., ryegrass, storage in vitro, tissue culture     

Leaf and Tiller Production of Prairie Grass (Bromus willdenowii Kunth) and Two Ryegrass (Lolium) Species

A detailed morphological study of three prairie grass cultivars(Bromus willdenowii Kunth) was conducted under ‘vegetative’and ‘reproductive’ growth conditions (short andlong photoperiods) and at different temperatures. Perennialryegrass (Lolium perenne L.) and Westerwolds ryegrass (Loliummuhiflorum Lam.) were compared during vegetative growth. Prairie grass had higher leaf appearance rates (leaves per tillerper day) and lower site filling (tillers per tiller per leafappearance interval) than the ryegrass species. Tillering rates(tillers per tiller per day) were also lower, except under vegetativeconditions at 4C. Low tiller number in prairie grass was notdue to lack of tiller sites but a result of poor filling ofthese sites. Lower site filling occurred because of increaseddelays in appearance of the youngest axillary tiller and lackof axillary tillers emerging from basal tiller buds. In prairiegrass, no tillers came from coleoptile buds while only occasionallydid prophyll buds develop tillers. Low tiller number in prairiegrass was compensated for by greater tiller weight. Prairiegrass had more live leaves per tiller, greater area per leafand a high leaf area per plant. Considerable variation between cultivars was found in prairiegrass. The cultivar ‘Bellegarde’ had high leaf appearance,large leaves and rapid reproductive development, but had lowlevels of site filling, tillering rate, final tiller numberand herbage quality during reproductive growth. ‘Primabel’tended to have the opposite levels for these parameters, while‘Grasslands Matua’ was intermediate and possiblyprovided the best balance of all plant parameters. prairie grass, Bromus willdenowii Kunth, perennial ryegrass, Lolium perenne L., Westerwolds ryegrass, Lolium multiflorum Lam., temperature, photoperiod, leaf appearance, leaf area, tillering, site filling, tillering sites, yield     

The Reciprocal Transfer of Radiocarbon between a Developing Tiller and its Parent Shoot in Vegetative Plants of Lolium multiflorum Lam.

The transfer of ¹⁴C-labelled assimilates between a tiller andits parent shoot was examined in young plants of Lolium multiflorumLam. Radiocarbon was exported freely from an expanded laminato sinks within the shoot axis from which it originated andto the root system. Lesser amounts of radiocarbon were exportedto the other shoot. It is suggested that the reciprocal exchangeof radiocarbon between tiller and main shoot occurred principallyvia a direct pathway through stem tissues rather than via apathway involving the roots.     

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 Regrowth Patterns and Carbohydrate Levels in Lolium multiflorum Lam.

The regrowth pattern in Lolium multiflorum was analysed in relationto carbohydrate levels and developmental characteristics, usingtwo contrasting populations. Liscate (a natural population collectedin Northern Italy) and the cultivar S 22, the former havingmore erect tillers, longer leaves and a lower rate of leaf appearance.The plants were grown in 16 h photoperiods, at 15/10 °C.NAR was lower in S. 22, but because LAR was higher as a resultof the greater SLA, the RGR was similar in Liscate and S. 22Starch levels were also similar in the two populations, butthe level of WSC was higher in Liscate than in S 22. When thetwo populations were defoliated to the same extent, total leafregrowth and rate of leaf elongation were greater in Liscate,but its tillering was more inhibited. Although the rates ofleaf regrowth were eventually similar in both populations, theywere initially lower in S. 22, leading to a higher total regrowthin Liscate. In both populations, WSC levels in the roots andstubble decreased after defoliation, but starch levels remainedunchanged. During regrowth in the dark, starch levels also decreased,but only when most of the WSC in the stubble was depleted. Lolium multiflorum Lam, Italian ryegrass, relative growth rate, net assimilation rate, leaf area ratio, specific leaf area, leaf weight ratio, carbohydrate     

The physiological response of winter wheat to reductions in plant density

The effects of reducing the plant density of winter wheat (cv. Haven) on canopy formation, radiation absorption and dry matter production and partitioning were investigated in field experiments in 1996/97 and 1997/98. Crop densities established ranged from 19 to 338 plants m^?2. Grain yield was maintained with large reductions in plant density. At low plant densities the relative growth rate of the crop increased allowing a maintenance of crop dry matter production. An 18 fold reduction in plant density led only to a six fold reduction in green area index at the beginning of stem extension and by anthesis the difference was less than two fold. Crops grown at low plant densities increased green area per plant through increased duration of tiller production, green area per shoot and shoot survival. Main stem leaf number, phyllochron and tiller production rate were not significantly affected by plant density. Radiation use efficiency was greater at the low plant densities. We propose that better radiation distribution through the canopy and increased canopy nitrogen ratio were the causative mechanisms for this increase in RUE. As a result of increased green area per shoot and a decrease in ear production, more radiation was absorbed per shoot at the low plant densities, allowing an increase in grain number per ear from 32 to 48.     

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     

Nitrate Accumulation and Osmotic Regulation in Italian Ryegrass (Lolium multiflorum Lam.)

The role of nitrate accumulation was studied in osmotic adaptationof Italian ryegrass (Lolium multiflorum Lam. cv. Romo). Plantswere grown under different light intensities (68 and 143 W m^–2)and on Hoagland nutrient solution with a solute potential of0.035 MPa and –0.335 MPa. The solute potential of thenutrient solution was decreased by addition of NaCl, which wastaken up by the plant, and PEG 6000 which was not. At each growingcondition the solute potential of the expressed plant sap wasconstant during the experimental period of 19 d, but was decreasedby increase in light intensity and addition of osmotic substancesin the root medium. At sugar concentrations between 20 and 60mg per gram plant water a change in sugar concentration is osmoticallyfully compensated for by an opposite change in nitrate concentration.At sugar concentrations lower than 20 mg per gram plant waterthere is an overcompensation of nitrate. The overcompensationincrease is attributed to a concomitant decrease of other organicsolutes such as amino acids and organic acids. When NaG is addedto the nutrient solution, the nitrate concentration in the plantdecreases and the solute potential is decreased by uptake ofchloride. With PEG the nitrate content of the plant also decreased.The solute potential of the plant sap is decreased by accumulationof sugar, at least at the high light intensity. Key words: Lolium multiflorum, Nitrate accumulation, Light intensity, Osmotic regulation     

Tillering Responses of Lolium multiflorum Plants to Changes of Red/Far-Red Ratio Typical of Sparse Canopies

Casal, J. J., Sáchez, R. A. and Deregibus, V. A. 1987.Tillering responses of Lolium multiflorum plants to changesof red/far-red ratio typical of sparse canopies.—J. exp.Bot. 38: 1432–1439. Plants of Lolium multiflorum were grown either in growth roomsunder radiation sources providing equivalent PAR but differentR/FR ratios between 0·46 and 2·36, or under sunlightsupplemented with a series of small fluence rates of FR throughoutthe photoperiod. In both kinds of experiments a reduction oftillering was found along with small depressions of R/FR ratiobelow the values typical of sunlight. In this range both thesquare-root-transformed rate of tillering and the site-fillingrate were linearly related to the estimated phytochrome photo-equilibriaand the slope was very steep under conditions that allowed hightillering rates. The addition of low fluence rates of red lightat the base of the shoots raised tillering of plants exposedto low R/FR ratios to the level of plants grown under high R/FRratios in spite of the ratios received by the rest of the plant.Moreover, irradiation of plant bases with intermediate-low R/FRratios reduced tillering indicating that this would be one siteof perception. These results show a high sensitivity to changesof R/FR ratio typical of different degrees of shade in sparsecanopies. This suggests that by monitoring these changes Loliummultiflorum plants would be able to perceive an anticipatedsignal of impending competition in growing canopies.     

Net assimilation rate and shoot area development in birch (Betula pendula Roth.) at different steady-state values of nutrition and photon flux density

Summary Small birch plants (Betula pendula Roth.) were grown in a climate chamber at different, exponentially increasing rates of nitrogen supply and at different photon flux densities. This resulted in treatments with relative growth rate equal to the relative rate of increase in nitrogen supply and with different equilibrium values of plant nitrogen concentration. Nitrogen productivity (rate of dry matter increase per plant nitrogen) was largely independent of nitrogen supply and was greater at higher photon flux density. Leaf weight ratio, average specific leaf area (and thus leaf area ratio) were all greater at better nitrogen supply and at lower values of photon flux density. The dependencies were such that the ratio of total projected leaf area to plant nitrogen at a given photon flux density was similar at all rates of nitrogen supply. The ratio was greater at lower values of photon flux density. At a given value of photon flux density, net assimilation rate and net photosynthetic rate per shoot area (measured at the growth climate) were only slightly greater at better rates of nitrogen supply. Values were greater at higher photon flux densities. Acclimation of the total leaf area to plant nitrogen ratio and of net assimilation rate was such that nitrogen productivity was largely saturated with respect to photon flux density at values greater than 230 mol m^-2 s^-1. At higher photon flux densities, any potential gain in nitrogen productivity associated with higher net assimilation rates was apparently offset by lower ratios of total leaf area to plant nitrogen.