Growth of Near-isogenic Wheat Lines Differing in Development--Plants in a Simulated Canopy

An understanding of the principal factors regulating the growthof temperate cereals will identify opportunities to manipulatecrop growth. In an accompanying paper (Gomez-Macpherson, Richardsand Masle,Annals of Botany82: 315–322, 1998), growth aroundthe start of floral initiation was studied in isogenic wheat(Triticum aestivumL.) lines grown as spaced plants. In thispaper, two of the same near-isogenic wheat lines were grownas mini-canopies in a growth chamber. The objective was to determinewhether results obtained using spaced plants also apply to plantsgrown in a simulated canopy as a first step to emulate fieldconditions. Biomass of plant organs, leaf area and leaf andtiller appearance were determined from sowing to ear emergenceof the early developing line. Contrary to results obtained usingspaced plants, lines differed in their above-ground biomassaccumulation, although total plant biomass accumulation wassimilar. After the early line reached terminal spikelet stage(TS), biomass partitioning to the roots and leaves decreased,whereas partitioning to the stem and ear increased. This resultedin a lower root:shoot ratio in the early flowering line thanin the late line which remained vegetative. Tiller senescencealso began after TS in the early line whereas no tiller senescencewas observed in the late line during the experiment. Furthermore,after TS, net assimilation rate was greater and leaf area ratiowas lower in the early line. It is suggested that, after reachingTS, plants grown in a canopy become source limited comparedto widely spaced plants, or compared to plants that have notreached TS, and this results in less root growth.Copyright 1998Annals of Botany Company Development, growth, partitioning,Triticum aestivumL., wheat.     

A Model to Simulate the Final Number of Reproductive Nodes in Pea (Pisum sativumL.)

The final number of reproductive nodes (TRN) is highly variablein pea under field conditions and can limit yield. However,the determinants of this variability are unknown. This is aproblem for crop managers and for many crop simulation models,in which the assimilate production and partitioning modulesgenerally depend on a phenological module including simulationof TRN. Previous studies in growth cabinets have linked theend of flowering to the presence of growing pods near the apex.We investigated the effects of the position of reproductiveorgans on the stem on the cessation of leaf emergence by analyticalexperiments involving pod removal. We then analysed whetherdevelopmental characteristics, obtained in the field for variousgenotypes, locations, sowing dates, plant nitrogen status, plantwater status and plant densities, could account for the observedvariation in the number of reproductive nodes. On the basisof these results, we constructed a simple model simulating TRNfrom three developmental parameters. The model was calibratedon cultivar ‘Solara’, evaluated for a wide rangeof situations and extrapolated to many genotypes, and was foundto have high predictive value.Copyright 1998 Annals of BotanyCompany Pisum sativumL., pea, number of reproductive nodes, model, genotype, N nutrition, pod removal, plant density, development, flowering, apical senescence     

Effects of the Photoperiod Genes Ppd1 and Ppd2 on Growth and Development of the Shoot Apex in Wheat

Two major genes influencing the photoperiod response in wheat,Ppd1 and Ppd2, have been identified on the group 2 chromosomes.Substitution lines, which had been characterized on the basisof time of ear emergence as carrying either the insensitiveor sensitive alleles of the two Ppd genes, were used to investigatethe effect of these genes on development. They were grown undershort photoperiods, and growth and development of the shootapex was measured. The primary influence of the Ppd genes was on ear growth. Inthe plants carrying the insensitive alleles, Ppd1 and Ppd2,the relative growth rate of the floral apex was faster thanthat of plants with the sensitive alleles, ppd1 and ppd2. Therewere no differences in the rate of spikelet initiation, butthe spikelets of the ppd lines grew and developed more slowly. The Ppd2 material segregated for another gene located on chromosome2B affecting duration of the life cycle. This gene also affectedthe relative growth rate of the ear. It was considered that the major effect of the Ppd1, Ppd2 andthe second genetic factor on chromosome 2B is on floral growthrate. Differences in apex morphology, stem growth and ear emergenceare thought to be due to the differences in floral apex growthand size. Wheat, photoperiod genes, shoot apex development, shoot apex growth     

Changes in Apical Growth and Phyllotaxis on Flowering and Reversion in Impatiens balsamina L.

When plants of Impatiens balsamina L were subjected to 5 shortdays and then re-placed in long days, they began to form a terminalflower and then reverted to vegetative growth at this terminalshoot apex The onset of flowering was accompanied by an increasein the rate of initiation of primordia, an increase in the growthrate of the apex, a change in primordium arrangement from spiralto whorled or pseudo-whorled, a lack of internodes, and a reductionm the size at initiation of the primordia and also of the stemfrusta which give rise to nodal and internodal tissues On reversion,parts intermediate between petals and leaves were formed, followedby leaves, although in reverted apices the size at initiationand the arrangement of primordia remained the same as in thefloweing apex The apical growth rate and the rate of primordiuminitiation were less in the reverted apices than in floral apicesbut remained higher than in the original vegetative apex Sincethe changes in apical growth which occur on the transition toflowering are not reversed on reversion, the development oforgans as leaves or petals is not directly related to the growthrate of the apex, or the arrangement, rate of initiation orsize at initiation of primordia Impatiens balsamina L, flower reversion, evocation, phyllotaxis, shoot meristem     

Morphogenetic Changes Induced by a Low Red: Far-Red Ratio and their Growth Consequences in Water Hyacinth (Eichhornia crassipes)

Plants of water hyacinth (Eichhornia crassipes) were grown undertwo red/far-red ratios (Z) to investigate the effects on morphologyand growth of the light quality component of canopy shade. Experimentswere conducted in diffuse sunlight in the presence or absenceof far-red radiation. Under low Z conditions, fewer new ramets were produced and theirstolons were shorter. The number of leaves per ramet was unchanged,but petiole length and blade area were increased. This changein biomass partitioning resulted in a lower investment in themain resource-acquiring organs (leaf blades and roots). Thelower allocation of biomass to the leaf blades was compensatedfor by a higher net assimilation rate, such that relative growthrate remained unchanged. Key words: Biomass partitioning, Eichhornia crassipes, growth, morphogenesis, red: far-red ratio     

Treatments that Enhance Flowering in the Post-inductive Period of a Short-day Plant, Chenopodium rubrum L.

Flowering was promoted in young plants of Chenopodium rubrumL. by application of growth inhibitors such as 5-fluorodeoxyuridine(FUDR) and (2-chloroethyl) trimethylammonium chloride (CCC),growth substances (indol-3yl-acetic acid, IAA), by the removalof roots and by drought. All the treatments were effective onlyduring the post-inductive period and at the threshold levelof photoperiodic induction. The response of plants was strictlytime-dependent. The experimental data indicate that the stimulationof flowering is usually accompanied by inhibition of leaf initiationand growth. The treatments probably produced variation in thequantitative expression of flowering by causing a shift in emphasisin the development of leaf and bud primordia at the shoot apex.The dynamic analysis of differentiation of the shoot apex indicatesa correlation between the morphological stage of the shoot apexand its responsiveness to the treatments.     

Temperature Response of Vernalization in Wheat: A Developmental Analysis

The vernalization response of wheat ( Triticum aestivum L.)was reinterpreted from a developmental perspective, using currentconcepts of the developmental regulation of wheat morphologyand phenology. At temperatures above 0 °C, the effects ofthe process of vernalization per se in wheat are confoundedby the effects of concurrent vegetative development. These effectsare manifested by differences in the number of leaves initiatedby the shoot apex prior to floral initiation, which in turnaffects the subsequent rate of development to ear emergenceand anthesis. Leaf primordia development during vernalizationand total leaf number at flowering were used to develop criteriato define both the progress and the point of saturation of thevernalization response. These criteria were then used to reinterpretthe results of Chujo ( Proceedings of the Crop Science Societyof Japan 35 : 177–186, 1966), and derive the temperatureresponse of vernalization per se for plants grown under saturatinglong day conditions. The rate of vernalization increased linearlywith temperature between 1 and 11 °C, such that the timetaken to saturate the vernalization response decreased from70 d at 1 °C to 40 d at 11 °C. The rate declined againat temperatures above 11 °C, and 18 °C was apparentlyineffective for vernalization. Total leaf number at saturation,however, increased consistently with temperature, as a resultof the balance between the concurrent processes of leaf primordiuminitiation and vernalization. Total leaf number at saturationincreased from 6 at 1 °C to 13.3 at 15 °C, which inturn influenced the time taken to reach ear emergence. The advantagesof using this developmental interpretation of vernalizationas the basis for a mechanistic model of the vernalization responsein wheat are discussed. Triticum aestivum L.; wheat; vernalization; rate; temperature; primordia; leaf number; flowering     

Apical Growth and Modification of the Development of Primordia During Re-flowering of Reverted Plants of Impatiens balsamina L

Impatiens balsamina L. was induced to flower by exposure to5 short days and then made to revert to vegetative growth byreturn to long days. After 9 long days reverted plants wereinduced to re-flower by returning them to short days. Petalinitiation began immediately and seven primordia already presentdeveloped into petals instead of into predominantly leaf-likeorgans. However, the arrangement of primordia at the shoot apex,their rate of initiation and size at initiation remained unchangedfrom the reverted apex, as did apical growth rate and the lengthof stem frusta at initiation. The more rapid flowering of thereverted plants than of plants when first induced, and the lackof change in apical growth pattern, imply that the revertedapices remain partially evoked, and that the apical growth patternand phyllotaxis typical of the flower, and already present inthe reverted plants, facilitate the transition to flower formation. Impatiens balsamina, flower reversion, partial evocation, shoot meristem, determination, leaf development     

Simulating Growth and Root-shoot Partitioning in Prairie Grasses Under Elevated Atmospheric CO2and Water Stress

We constructed a model simulating growth, shoot-root partitioning,plant nitrogen (N) concentration and total non-structural carbohydratesin perennial grasses. Carbon (C) allocation was based on theconcept of a functional balance between root and shoot growth,which responded to variable plant C and N supplies. Interactionsbetween the plant and environment were made explicit by wayof variables for soil water and soil inorganic N. The modelwas fitted to data on the growth of two species of perennialgrass subjected to elevated atmospheric CO₂and water stresstreatments. The model exhibited complex feedbacks between plantand environment, and the indirect effects of CO₂and water treatmentson soil water and soil inorganic N supplies were important ininterpreting observed plant responses. Growth was surprisinglyinsensitive to shoot-root partitioning in the model, apparentlybecause of the limited soil N supply, which weakened the expectedpositive relationship between root growth and total N uptake.Alternative models for the regulation of allocation betweenshoots and roots were objectively compared by using optimizationto find the least squares fit of each model to the data. Regulationby various combinations of C and N uptake rates, C and N substrateconcentrations, and shoot and root biomass gave nearly equivalentfits to the data, apparently because these variables were correlatedwith each other. A partitioning function that maximized growthpredicted too high a root to shoot ratio, suggesting that partitioningdid not serve to maximize growth under the conditions of theexperiment.Copyright 1998 Annals of Botany Company plant growth model, optimization, nitrogen, non-structural carbohydrates, carbon partitioning, elevated CO₂, water stress,Pascopyrum smithii,Bouteloua gracilis, photosynthetic pathway, maximal growth     

Long-term responses of Melilotus segetalis to salinity. I. Growth and partitioning

Annual sweetclover plants [Melilotus segetalis (Brot) Ser.] were grown for a complete life cycle with and without saline (NaCl treatment of CE=15 dS m⁻¹). Growth and partitioning analyses were performed. Sequential harvests (every 15 d) during the life cycle, and separation of plant material into roots, stems, petioles, leaves and reproductive structures were carried out Salt treatment reduced growth during the early and middle stages of the life of the plant, but did not significantly affect RGR in the reproductive phase. The root–shoot allometric coefficient of salinized plants in the generative phase decreased more than in control plants. We suggest that salinity-induced growth reduction in M. segetalis was primarily a result of a lower unit leaf rate (ULR) despite an increased leaf area ratio (LAR). Earlier flowering, higher biomass allocation to shoot and greater reproductive investment, but similar relative growth rate (RGR), were some of the main characteristics of salt-stressed plants compared to controls during the reproductive phase, these apparently being associated with increased sink strength caused by developing flowers and fruits.     

The role of apical development around the time of leaf initiation in determining leaf width at maturity in wheat seedlings (Triticum aestivum L.) with impeded roots

High soil resistance to root penetration (measured as penetrometerresistance, R_s slows down leaf growth and reduces mature leafsize in wheat seedlings {Triticum aestivum L.). Underlying changesin the kinetics of cell partitioning and expansion and in thesize and organization of mature cells were reported in companionpapers (Beemster and Masle, 1996; Beemster et al., 1996). Inthe present study, the relationships between apex growth, primordiuminitiation and expansion were analysed for plants grown at contrastingR_s, focusing on a leaf whose whole development proceeded afterthe onset of root impedance (leaf 5). High R_s reduced the rates of apex and leaf development, butdid not appear to have immediate effects on the pattern of developmentof the newly initiated phytomers. During an initial short period,the rate of development of a leaf primordium and associatednode were related to plastochronic age, according to similarrelationships (slopes) at the two R_s. Effects on developmentalpatterns were first detected on phytomer radial expansion duringplastochron 2. The ontogenetic pattern of leaf elongation wasaffected later, during the next few plastochrons preceding leafemergence (‘post-primordial stage’). It is concludedthat a reduction in the number of formative divisions and inthe number of proliferative cells along the intercalary mer-istemreported earlier (Beemster and Masle, 1996; Beemster et al.,1996) is not related to the size of the apical dome at leafinitiation nor to the size and number of meristematic cellsinitially recruited to the leaf primordium, which were all unaffectedby R_s. Rather they are generated at the primordial and post-primordialstages. Key words: Wheat, apex development, leaf primodium development, mature leaf width, root impedance     

Relative Nitrogen Limitation at Steady-state Nutrition as a Determinant of Plasticity in Five Grassland Plant Species

Partitioning of biomass between roots and different shoot partshas often been used to explain the response of plants to variationsin resource availability. There are still many uncertaintiesin the importance of this trait for plant performance, and clearguidelines on how partitioning should be quantified in relationto growth rate and resource supply are of fundamental importancefor such an understanding. This paper reports an attempt toshow how plant nitrogen status relates to root:shoot partitioningand other plastic responses, in a manner that can be used forquantitative predictions. The reactions to nitrogen limitationof five grassland plant species, with different ecological demands,were compared. The species used were the forbs Polygala vulgarisand Crepis praemorsa, and the grasses Danthonia decumbens, Agrostiscapillaris and Dactylis glomerata. The experiment was conductedin a climate chamber where the plants were grown hydroponically(1) under non-limiting nutrient conditions and (2) at a steady-statenitrogen limitation, which enabled the plants to express halfof their growth potential. The relative growth rate (RGR) ofthe species was strongly related to plant nitrogen concentration(PNC) and leaf area ratio (LAR), whereas the effects on netassimilation rate (NAR) were very small. Despite large differencesin maximum relative growth rate, the species showed remarkablesimilarities in dry matter partitioning between root and shoot.It is concluded that root:shoot partitioning can be treatedas a direct function of the relative resource limitation ofthe plant. The difficulty of attaining well-defined levels ofresource limitation in soil, other solid substrates and manyhydroponic systems may be the most important reason for thedivergent results in earlier studies. Better knowledge of soil-rootinteractions, and plant responses to the whole span of resource-supplylevels, is required for a thorough understanding of how nutrientslimit growth. Copyright 1999 Annals of Botany Company Growth rate, plant strategies, plasticity, partitioning, biomass, nitrogen, nutrient limitation, grassland.     

The Control of Flowering in Wheat and Barley: What Recent Advances in Molecular Genetics Can Reveal

The combined forces of developmental biologists, studying primordiuminitiation at the stem apex, and mathematical modellers, developingsimulations of crop growth and development, have brought aboutconsiderable advances in the understanding of the control offlowering in wheat and barley. Nevertheless, there are stillmajor gaps in this understanding including: what determinesthe basic rate of development (magnitude of the phyllochronor plastochron); how temperature and photoperiod interact tobring about the transition from vegetative to reproductive development;and how flowering occurs eventually in the absence of inductiveconditions. Although geneticists have tended to measure cerealflowering in terms of ‘days from sowing or emergence toheading’, results of studies using aneuploids and molecularmarkers are compatible with the roles for photoperiod and low-temperaturevernalization established in purely-physiological or developmentalinvestigations. They have also revealed the existence of ‘earlinessperse’loci, whose detailed roles have yet to be established.Progress towards isolating and characterizing wheat and barleyloci is hampered by the poor resolution of mapping (locationto a precision of tens of thousands of base pairs). Neitherof these broad approaches promises a rapid resolution of thefactors controlling the induction of flowering. Two expandingareas of molecular genetics now provide potential for greaterunderstanding of cereal flowering. First, the extensive homoeologyamong members of the Gramineae can be employed to establishthe existence and location of genes or quantitative trait lociin rice which correspond to controlling loci in wheat or barley.Since the rice genome is 1/30th of the size of the wheat genome,the accuracy of mapping loci can be much higher, and there isgreater potential for precise location of loci using techniquessuch as chromosome walking. With the ultimate cloning of individualgenes, and the isolation of gene products, the relative rolesof the 20 loci apparently involved in the induction of floweringof wheat could be explored. However, progress in the moleculargenetics ofArabidopsis(the second area) may provide a more rapidroute to understanding the control of flowering in cereals forseveral reasons: its small genome (1/4 that of rice); the likelihoodof extensive homoeology with cereals, in spite of differencesin codon usage between monocots and dicots; the existence ofa wide range of flowering-time mutants; and the control of floralinduction by a similar range of environmental factors includingphotoperiod and low temperature. It is likely that the MCDK(Martinez-Zapater, Coupland, Dean and Koornneef, 1994. In: MeyerowitzEM, Somerville CR.Arabidopsis.New York: Cold Spring Harbor Laboratory,403–433) model, formulated to explain the genetic andenvironmental control of flowering inArabidopsis,could be employedusefully in the formulation of experimental work on floweringin wheat and barley. This paper reviews these issues, payingparticular attention to the significance of ‘earlinessperse’ loci and the ‘constitutive floral pathway’for wheat and barley.Copyright 1998 Annals of Botany Company Wheat, barley, rice,Arabidopsis,flowering, photoperiod, vernalization, genetics, development.     

Analysis of Dry Matter Partitioning in Dactylis glomerata during Vegetative Growth Using a Carbon Budget Model

The dry matter partitioning in vegetative plants of Dactylisglomerata was studied from experiments performed in controlledenvironments. Plants were grown hydroponically in growth chambers,at two constant temperatures (17 and 25 °C). In both experimentsthe root fraction decreased regularly with time, an effect thatwas more accentuated in the higher temperature regime. In orderto explain the change in dry matter partitioning, the experimentalshoot and root growth were analysed using a carbon budget modelwhich includes shoot and root maintenance requirements. Themodel predicts a relationship between the root specific growthrate and the product of shoot specific growth rate and shootto root dry weight ratio. In the range of experimental accuracy,this relationship was found to be linear at both temperatures,which should indicate that the partitioning coefficients andthe root maintenance coefficient remained constant during vegetativegrowth. The effect of temperature on the value of these coefficientscan be specified from a linear regression analysis. Between17 and 25 °C, the root maintenance coefficient increasedby about a factor of two, whereas the partitioning coefficientsdid not vary significantly. On the basis of these results, itwas shown that the decrease in root fraction during vegetativegrowth should be mainly attributed to the decrease in net specificactivity of shoots.Copyright 1994, 1999 Academic Press Dactylis glomerata L., vegetative growth, model, partitioning, root:shoot ratio, shoot specific activity, maintenance requirements     

Enhancement of Drought-Induced Senescence by the Reproductive Sink in Fertile Lines of Wheat and Sorghum

The leaf senescence pattern was examined in water-stressed malesterile and fertile lines of wheat (Triticum aestivum) and sorghum(Sorghum vulgare). The study was conducted at the seedling stageand during grain development. The loss of leaf area and chlorophyllcontent induced by water stress was similar in the male sterileand fertile lines of wheat at the seedling stage. At the grainfilling stage, leaf senescence occurred at a faster rate inthe fertile lines as compared to sterile lines of both wheatand sorghum. The study indicates that a reproductive sink accentuatesdrought-induced leaf senescence. Drought resistance, leaf senescence, male sterile, sink     

Expression of Vernalization Genes in Near-isogenic Wheat Lines: Effects of Night Temperature

Four near-isogenic lines of wheat (Triticum aestivum L.em Thell)were used to compare selected night temperatures for their effectivenessas vernalizing temperatures. All treatments (conducted withina phytotron) had a common day temperature of 20 °C for 12h and night temperatures were 4, 7, 10, 13 and 20 °C. Interpretationof results for reproductive development was confounded by threeinteracting factors, their relative importance varying withgenotype. Firstly, development rate was generally slower atlower night temperatures. Secondly, in contrast, there was atendency for lower night temperatures to hasten developmentrate if vernalization requirements were satisfied. Thirdly,the lower night temperatures provided a more favourable environmentfor leaf production such that for some genotypes, vernalizedplants had higher final leaf numbers than unvernalized plants.Only for the genotype with the strongest vernalization response(vrn1 vrn2) did hastening of development due to vernalizationoverride any delaying effects. For this genotype, 4, 7 and 10°C were vernalizing temperatures. For the other three genotypes,any hastening of development due to vernalization was outweighedby delaying effects of lower night temperatures. Spikelet numberand days to anthesis were positively correlated in three ofthe four genotypes. It appeared that differences in spikeletnumber were a direct result of night temperature influencingthe duration of the spikelet phase and/or rate of spikelet initiation.Plant size at flowering was determined by the differential effectsof night temperature on growth and development rates. Triticum aestivum L., wheat, vernalization, night temperature, isogenic lines     

Determination of a Critical Nitrogen Dilution Curve for Winter Oilseed Rape

Several controlled environmental and field experiments werecarried out to define the critical nitrogen dilution curve forwinter oilseed rape, cultivar Goeland. This curve is describedby the following power equation:N=4.48 W^-0.25,whereNis the totalnitrogen concentration in the shoot biomass andWthe shoot biomass.This curve has been validated over the range of shoot dry matterof 0.88 to 6.3 t ha^-1. For lower shoot biomasses this equationoverestimated the critical nitrogen concentration; we proposea constant value of 4.63 (Nis expressed in reduced N, whichis a more stable N fraction in the shoot at these stages ofdevelopment). These results have been validated in several pedoclimaticconditions in France on a single variety in 1994 and 1995. Thehigher position of this curve relative to the C₃species referencecurve (Greenwoodet al.,Annals of Botany67: 181–190, 1990)can be explained by the experimental conditions obtained byGreenwoodet al. (1990); therefore, all their rape data are ratherclose to the critical curve that we propose. The differencesfound between wheat and winter oilseed rape critical N dilutioncurves correspond to their respective leaf:stem dry matter ratioand the specific leaf loss phenomenon occuring in rape. Winteroilseed rape has a higher capacity of N accumulation in itsshoot than wheat for the same aerial dry matter. The proportionof nitrate in shoots rises with the nitrogen nutrition index(N.N.I.) and is more important for rapeseed than for wheat forthe same N.N.I. This difference is especially high at the beginningof flowering when the shade provided by the canopy of rapeseedflowers decreases nitrate reductase activity.Copyright 1998Annals of Botany Company Winter oilseed rape;Brassica napusL.; plant N concentration; nitrate; reduced N; shoot biomass; critical nitrogen concentration; dilution curve; N productivity.     

THE GROWTH OF THE STEM TIP OF KALANCHOËU CV. ‘BRILLIANT STAR’

Stein , Diana B. and o . L. Stein . (Montana State U., Missoula.) The growth of the stem tip of Kalanchoë cv. ‘Brilliant Star.‘ Amer. Jour. Bot. 47 (2) : 132—140. Illus. I960.–The purposes of this investigation were (1) to define as clearly as possible the events in the shoot apex and its immediate derivatives during the ontogeny of the shoot; and (2) to determine the changes which occur during the transition from a vegetative to a reproductive meristem. Rate of leaf production in Kalanchoë is basically constant. The rate of leaf growth subsequent to the early primordial state is, however, dependent on the age of the plant and on the environment in which the plant is grown. By keeping these factors constant a correlation can be demonstrated between the size of the youngest visible leaf and the microscopic primordia. Throughout its ontogeny the general architecture of the shoot apex remains essentially the same. Two tunica layers cover the corpus in the vegetative shoot apex, and even in the flowering meristem these 2 layers can be detected. The apex is essentially flat and blends into the adjacent leaf primordia early in the plastochron. About 10 days after flower induction has been started the apex changes its form to a dome, primarily by increased cell division. At the same time the rate of elongation of the youngest internodes increases thus placing the flowering stem tip atop an elongated stem. Axillary development is ultimately responsible for the development of a dichasium.     

Effect of Root and Shoot Meristem Temperature on Shoot to Root Dry Matter Partitioning and the Internal Concentrations of Nitrogen and Carbohydrates in Maize and Wheat

Maize (Zea mays L.) and spring wheat (Triticum aestivum L.)were grown in nutrient solution at uniformly high air temperature(20 °C), but different root zone temperatures (RZT 20, 16,12 °C). To manipulate the ratio of shoot activity to rootactivity, the plants were grown with their shoot base includingthe apical meristem either above (i.e. at 20 °C) or withinthe nutrient solution (i.e. at 20, 16 or 12 °C). In wheat, the ratio of shoot:root dry matter partitioning decreasedat low RZT, whereas the opposite was true for maize. In bothspecies, dry matter partitioning to the shoot was one-sidedlyincreased when the shoot base temperature, and thus shoot activity,were increased at low RZT. The concentrations of non-structuralcarbohydrates (NSC) in the shoots and roots were higher at lowin comparison to high RZT in both species, irrespective of theshoot base temperature. The concentrations of nitrogen (N) inthe shoot and root fresh matter also increased at low RZT withthe exception of maize grown at 12 °C RZT and 20 °Cshoot base temperature. The ratio of NSC:N was increased inboth species at low RZT. However this ratio was negatively correlatedwith the ratio of shoot:root dry matter partitioning in wheat,but positively correlated in maize. It is suggested that dry matter partitioning between shoot androots at low RZT is not causally related to the internal nitrogenor carbohydrate status of the plants. Furthermore, balancedactivity between shoot and roots is maintained by adaptationsin specific shoot and root activity, rather than by an alteredratio of biomass allocation between shoot and roots.Copyright1994, 1999 Academic Press Wheat, Triticum aestivum, maize, Zea mays, root temperature, shoot meristem temperature, biomass allocation, shoot:root ratio, carbohydrate status, nitrogen status, functional equilibrium     

Evaluation of a Dynamic Simulation Model for Tomato Crop Growth and Development

A dynamic simulation model for tomato crop growth and development,TOMSIM, is evaluated. Potential crop growth and daily crop grossassimilation rate (P_gc,d) is computed by integration of leafassimilation rates over total crop leaf area throughout theday. Crop growth results fromP_gc,dminus maintenance respirationrate (R_m), multiplied by the conversion efficiency. Dry matterdistribution is simulated, based on the sink strength of theplant organs, which is quantified by their potential growthrate. Within the plant, individual fruit trusses and vegetativeunits (three leaves and stem internodes between two trusses)are distinguished. Sink strength of a truss or a vegetativeunit is described as a function of its developmental stage.In this paper, emphasis is on the interactions between the twosubmodels of, respectively, dry matter production and dry matterdistribution. Sensitivity analysis showed that global radiation,CO₂concentration, specific leaf area (SLA) and the developmentalstage of a vegetative unit at leaf pruning had a large influenceon crop growth rate, whereas temperature, number of fruits pertruss, sink strength of a vegetative unit and plant densitywere less important. Leaf area index (LAI) was very sensitiveto SLA and the developmental stage of a vegetative unit at leafpruning. Temperature did not influence the simulated R_m, asincreased respiration rate per unit of biomass at higher temperatureswas compensated by a decrease in biomass. The model was validatedfor four glasshouse experiments with plant density and fruitpruning treatments, and on data from two commercially growncrops. In general, measured and simulated crop growth ratesfrom 1 month after planting onwards agreed reasonably well,average overestimation being 12%. However, crop growth ratesin the first month after planting were overestimated by 52%on average. Final crop dry mass was overestimated by 0–31%,due to inaccurate simulation of LAI, resulting partly from inaccurateSLA prediction, which is especially important at low plant densityand in a young crop.Copyright 1999 Annals of Botany Company Crop growth, dry matter production, glasshouse, leaf area,Lycopersicon esculentum, partitioning, simulation model, tomato, TOMSIM.