Effect of Photoperiod on Vegetative Growth in Two Natural Populations of Dactylis glomerata L.

The growth of two natural populations of cocksfoot from contrastingclimatic regions (Norway and Portugal) was studied at four temperaturesand two photoperiods. Serial harvests were taken and quadraticcurves were fitted to log dry weight and leaf area for eachreplicate in order to calculate growth attributes at a constantplant weight for all treatments. Interactions of population,temperature, and photoperiod on relative growth-rate (RGR) werefound, with the greatest population differences at 5 and 30°C in an 8-h photoperiod. Leaf-area ratio (LAR) played alarger part than net assimilation rate (NAR) in determiningthe differential population responses in RGR to daylength, andthese differences in LAR were primarily the result of differentpatterns of dry-matter distribution within the plant.     

The Effect of Temperature on Vegetative Growth in Climatic Races of Dactylis glomerata in Controlled Environments

The growth patterns in two natural populations of Dactylis glomeratafrom contrasting climatic regions, Norway and Portugal, werestudied at four constant temperatures (5, 10, 20, and 30°C) in a 16-h photoperiod. Marked changes in relative growth-rateat different temperatures were positively correlated with changesin both net assimilation rate and leaf-area ratio, whereas differencesbetween the populations in the relative growth-rate were theresult of differences in net assimilation rate, and were negativelycorrelated with differences in leaf-area ratio. The changesin leaf-area ratio at different temperatures were correlatedwith changes in leaf morphology and distribution of assimilateswithin the plant. The possible adaptive advantage of these vegetativegrowth patterns is discussed in relation to the survival ofthe plants in the original environments.     

Analysis of the Time Course of Change in Nitrogen Content in Dactylis glomerata L. Using a Model of Plant Growth

The growth, root fraction and nitrogen content of Dactylis glomerataL. grown hydroponically in constant environmental conditions,were measured in the vegetative phase. The variation of theseparameters denotes a progressive change in the chemical compositionof the plant, which can be attributed to changing proportionsof structural material, which is immediately available for growth,and storage material. On the basis of a kinetic model of plantgrowth, a definition of the two components was proposaed, whichled us to derive a relationship between relative growth rateand nitrogen content. This relationship was found to be compatiblewith experimental data. Dactylis glomerata L., vegetative phase, kinetic model, growth rate, nitrogen content     

A Model to Describe the Partitioning of Photosynthate during Vegetative Plant Growth

An approach is described to the problem of modelling quantitativelythe partitioning of photosynthate during vegetative plant growth.Two plant processes are important in the scheme: the first ofthese is the utilization of substrate for growth and how thisutilization depends upon substrate concentration, the secondconcerns the transport of substrate between different plantparts and how this depends upon the substrate concentrationsin the plant parts. In both cases simple phenomenological relationshave been assumed which seem to be in reasonable accord withexperimental data and with more basic theoretical considerations.The model is able to describe some of the features of steady-statevegetative plant growth in a natural manner. The limitationsof the present formulation are considered, and the implicationsof this type of approach for whole-plant models are discussed.     

A Simulation Model for Dry Matter Partitioning in Cucumber

A dynamic model is developed for the simulation of the dailydry matter distribution between the generative and vegetativeplant parts and the distribution among individual fruits ingreenhouse cucumber. The model is based on the hypothesis thatdry matter partitioning is regulated by the sink strengths ofthe plant organs. The sink strength of an organ is defined hereas its potential growth rate, i.e. the growth rate at non-limitingassimilate supply. The sink strength of each individual fruitis described as a function of its temperature sum after anthesisand the actual temperature, that of the vegetative plant partsas a function of actual temperature only. The formation rateof non-aborting fruits is essentially a function of the source/sinkratio. Model results agreed well with the measured fluctuating distributionof dry matter between fruits and vegetative parts. The measuredeffects of three intensities of fruit removal were also simulatedsatisfactorily. When simulating the partitioning among individualfruits the final fruit size was simulated quite well. However,the growth rate of young fruits was usually overestimated andthat of old fruits underestimated, because of dominance amongfruits. This phenomenon could be accounted for by incorporatingpriority functions into the model. Finally, a sensitivity analysisof the model was performed to investigate the effects of someclimatic factors, manipulations of the number of fruits on aplant and model parameters on dry matter distribution. Strategiesto manipulate the dry matter distribution are discussed.Copyright1994, 1999 Academic Press Cucumber, Cucumis sativus (L.), dry matter distribution, fruit growth, partitioning, simulation model, source-sink     

Dry Matter Partitioning in Tomato: Validation of a Dynamic Simulation Model

A model for dynamic simulation of dry matter distribution betweenreproductive and vegetative plant parts and the distributionamong individual fruit trusses in glasshouse tomato, is validated.The model is part of the crop growth model TOMSIM and is basedon the hypothesis that dry matter distribution is regulatedby the sink strengths of the plant organs, quantified by theirpotential growth rates, i.e. the growth rates at non-limitingassimilate supply. Within the plant, individual fruit trussesare distinguished and sink strength of a truss is describedas a function of its development stage. Truss development rateis a function of temperature only. The same potential growthcurve, proportional to the number of fruits per truss, is adoptedfor all trusses. In a simple version of the model, vegetativeplant parts are lumped together as one sink with a constantsink strength. In a more detailed version, vegetative sink strengthis calculated as the sum of sink strengths of vegetative units(three leaves and stem internodes between two trusses). The model was validated for six glasshouse experiments, coveringeffects of planting date, plant density, number of fruits pertruss (pruning at anthesis), truss removal (every second trussremoved at anthesis), single- and double-shoot plants and atemperature experiment conducted in climate rooms at 17, 20or 23 °C. Daily increase in above-ground dry weight, averagedaily temperatures and number of set fruits per truss were inputsto the model. Both the simple and the more detailed model showedgood agreement between measured and simulated fraction of drymatter partitioned into the fruits over time. For the simpleversion of the model, the slope of the lines relating simulatedto measured fraction partitioned into the fruits (16 data sets),varied between 0.92 and 1.11, on average it was 1.04, implying4% over-estimation for this fraction. For the detailed modelthese numbers were slightly better: 0.89, 1.08 and 1.01, respectively.The temperature experiment revealed no important direct influenceof temperature on the ratio between generative and vegetativesink strength. Simulated truss growth curves showed reasonableagreement with the measurements, although both models over-estimated(17% on average) final dry weight of the lower trusses (truss1 –3) on a plant. Modelling dry matter partitioning basedon sink strengths of organs is promising, as it is a general,dynamic and flexible approach, showing good agreement betweenmeasurements and simulation for a range of conditions. Applicabilityof the model is, however, still limited as long as the numberof fruits per truss (flower and /or fruit abortion) is not simulated,as this is a major feedback mechanism in plant growth. Dry matter distribution; sink strength; glasshouse; model; partitioning; simulation; temperature; tomato; TOMSIM; validation     

Shoot-Root-Nodule Partitioning in a Vegetative Legume--A Model

A dry-matter partitioning model of a vegetative legume whichis both utilizing nitrate nitrogen and carrying out N₂ fixationis described. It is an extension of a previously described root-shootmodel, and is based on assumed transport pathways for carbonand nitrogen substrates, and utilization of those substratesfor structural growth. The model is used to examine the consequencesof varying the photosynthetic activity, the nitrate uptake activity,and the N₂ fixation activity on the patterns of dry-matter partitioningand substrate fluxes within the plant. The predictions of themodel agree with physiological expectation, and the model cantherefore be used to provide an interpretation of experimentalobservations of such plant and crop responses. Model, partitioning, legume, nitrogen fixation     

A Model of the Partitioning of New Above-ground Dry Matter

A model for the partitioning of new above-ground dry matterof a vegetative dicotyledonous plant is developed. It assumestwo distinct functional components of the stem tissues. One,the primary stem tissue, includes physiologically active tissuessuch as xylem, phloem and meristematic tissues, and the other,secondary stem tissue, includes the main mechanical structures.The model is used to examine the partitioning of dry matterbetween leaf and stem tissues, and its behavour is comparedwith experimental observations. Partitioning, leaf, stem, secondary stem tissues     

The Effect of Defoliation on the Carbon Balance in Dactylis glomerata

Measurements were made of the carbon dioxide exchange of rootsand shoots, changes in soluble carbohydrates, rates of rootextension, and rate of phosphorus uptake of young plants ofDactylis glomerata (Cocksfoot) during eight days following defoliation.The results indicated that the soluble carbohydrates formedpart of a labile pool which was used in respiration and forproviding substrates for new growth. Where defoliation was notsevere, the changes in reserve carbohydrates could account fornet respiratory losses and amounts of new growth made. Wheredefoliation was severe, even high concentrations of reservecarbohydrates were inadequate and other substances, presumablyproteins, must have been remobilized for use in respirationand new growth. The content of soluble carbohydrate in the root was completelyinadequate to meet the needs of root respiration; transfer fromthe tops and/or remobilization of other substances in the rootsmust have occurred. Following a severe defoliation, root extension stopped and ratesof respiration and phosphorus uptake fell markedly. Phosphorusuptake remained at a low level for the eight days considered.After a light defoliation the roots recovered relatively rapidly. It is suggested that, following a severe defoliation, regrowthduring the first week is limited in turn first by the solublecarbohydrate content in the bases of expanding leaves, thenby the rate of photosynthesis, and then in the later Stagesby the rate of nutrient uptake sustained by the roots.     

Diurnal Fluctuations in Growth and CO2 Exchange in Dactylis glomerata

Diurnal fluctuations in dry matter accumulation and leaf extensionof seedlings of Dactylis glomerata were followed through a 16-hlight period and a subsequent 8-h dark period at 20 °C.Themeasured increase in dry weight during the light period andthe decrease during the dark period showed a very good agreementwith calculated dry weight changes derived from the rates ofcarbon dioxide exchange of whole seedlings. Although dry weightof the leaf blades decreased during the dark period, leaf expansioncontinued throughout the 24-h period with associated changesin the ratio of fresh weight to dry weight of the leaf blades.     

The Effects of Temperature on Vegetative and Early Reproductive Growth of a Cold-Tolerant and, a Cold-Sensitive Line of Phaseolus vulgaris L. 1. Nodulation, Growth and Partitioning of Dry Matter, Carbon and Nitrogen

Nodulated plants of a cold-sensitive (Seafarer, SF) and tolerant(accession 194) line of Phaseolus vulgaris L. were grown underthree temperature regimes, 15/10, 20/15 and 25/15 C (light/dark).Dry matter, total C and N were measured in plant parts at threeharvests. Both lines produced functional nodules at a mean growthtemperature as low as 12.9 C (15/10) but 194 produced moreand larger nodules which fixed more N (total plant N) than SF.At the lowest temperature during early vegetative growth, 194accumulated greater amounts of d. wt than SF but had similarRGR and NAR. RLGR and RGR expressed in terms of N on the otherhand, were markedly greater in 194 than SF. 194 Partitionedmore d. wt and N into shoots vs roots and had a lower leaf:stem d. wt ratio than SF. Both lines showed similar increasesin leaf area, leaf area ratio and RGR with increasing temperature. The results suggest that the ability to nodulate well, increasenodule size in response to temperature stress and achieve maximumleaf expansion are important factors for the superior growthof 194 over SF. Phaseolus vulgaris, common bean, nodulation, growth, low temperature stress     

Nitrogen Uptake and Plant Growth II. An Empirical Model of Vegetative Growth and Partitioning

An empirical model of vegetative plant growth is presented.The model is based on experimental data on Polygonum cuspidatum,which showed (1) that the partitioning of dry matter and nitrogenamong organs was linearly related to the nitrogen concentrationof the whole plant and (2) that leaf thickness was negativelycorrelated with leaf nitrogen concentration. The model properlydescribes the behaviour of plants. Steady-state solutions ofthe model give the relative growth rate, specific leaf weight,and partitioning of dry matter and nitrogen among organs withthe net assimilation rate and the specific absorption rate asenvironmental variables. The effect of nitrogen removal on drymatter and nitrogen partitioning was examined as non-steady-statedynamic solutions of the model. The model predicted not onlyreduced leaf growth and enhanced root growth but also a fluxof nitrogen from the leaf to the root, which agreed with theexperimental results. Mathematical model, partitioning of dry matter and nitrogen, plant nitrogen, relative growth rate, shoot: root ratio, specific leaf weight     

Growth reductions in cocksfoot (Dactylis glomerata L.) as a result of SO2 pollution

The effects of exposing Dactylis glomerata L. to 11 pphm SO₂ for four weeks were investigated using a wind tunnel fumigation system. The pollutant was found to cause significant reductions in the numbers of tillers and green leaves, leaf area, root/shoot ratio and all dry weight fractions measured. The percentage yield reductions found for D. glomerata were compared with those previously found for Lolium perenne L. under the same conditions of exposure. It was concluded that D. glomerata may be slightly more sensitive to SO₂ than L. perenne. The magnitudes of the yield reductions found in these experiments are greater than those previously reported and this is discussed in relation to the rate of air movement through the fumigation system. It is concluded that the effects of SO₂ on plants in the field, and subsequent losses in the yields of crops, may have been under-rated in the past.     

Effect of Nitrate Concentration on the Root: Shoot Ratio in Dactylis glomerata L. and on the Kinetics of Growth in the Vegetative Phase

The vegetative growth of Dactylis glomerata L. in sand was studiedunder controlled light, temperature, and nutritional conditions.Plants were daily supplied with three nutrient solutions ofdifferent nitrate concentrations (10^–2, 10^–3 and2 x 10^–4 mol I^–1). For each concentration, growthobeyed an exponential law between the fourth and seventh weeksafter sowing. The time constant of the exponential was the samefor the shoot as for the root, and showed no significant variationwith nitrate concentration. The kinetic results and the strong dependence of the root: shootratio on nitrate concentration are discussed on the basis ofThornley's model. Hypothesizing that the molecular mechanismsof nitrate absorption are independent of the nitrate concentrationof the nutrient solution, we derived a relationship betweenthe root: shoot ratio and nitrate concentration. This relationshipwas found to be compatible with the experimental results. Dactylis glomerata L., vegetative phase, kinetics of growth, root: shoot equilibrium, nitrate absorption     

Above- and Below-ground Growth of Forest Stands: a Carbon Budget Model

The utilization and allocation of carbon by a forest stand areexamined through a simple dynamic, mechanistic model which incorporatesradiation interception, photosynthesis, respiration, assimilatepartitioning, litterfall, root mortality and turnover. Qualitativemathematical analysis of the balance between carbon gains andlosses provides an intuitive insight into the determinants ofabove- and below-ground growth. The patterns of dry matter accumulationproduced by the model are compared with observed trends in standdevelopment. Reported differences between biomass distributionon sites of high and low productivity are reproduced by adjustingthe coefficients of assimilate partitioning. Forest stand growth, model forest growth, carbon budget, photosynthesis, assimilate partitioning     

A Model of the Partitioning of Growth between the Shoots and Roots of Vegetative Plants

A model of the partitioning of new growth between the shootsand roots of vegetative plants is presented. There are two partitioningfunctions, involving one partitioning parameter, which describethe priorities for new growth in both the shoots and roots.The dynamic responses, to changes in the environment and toshoot defoliation, of shoot and root specific growth rates,shoot: root ratio, and carbon and nitrogen substrate levels,are examined; realistic behaviour is observed. Balanced exponentialgrowth solutions are also examined and it is concluded thatrelationships between some derived plant growth quantities maybe non-unique, thus emphasizing the need for a critical understandingof the underlying physiological processes involved in plantgrowth. Mathematical model, partitioning of assimilates, shoot: root ratio, specific growth rate, carbon and nitrogen substrate levels     

Compensatory Changes in the Partitioning of Dry Matter in Relation to Nitrogen Uptake and Optimal Variations in Growth

Equations are derived relating relative growth rate (RGR) toroot:shoot ratio, root length, nitrogen inflow rate, leaf area,photosynthesis and carbon and nitrogen concentrations in theplant. The extents to which changes in specific root lengthand root: shoot ratio can compensate for the effects of lowN availability upon RGR are examined. Such responses could haveseveral compensatory functions: maximizing RGR; maintaininggrowth in which the activities of root and shoot limit RGR equally;and maximizing the efficiency of increase in RGR. Growth, nitrogen, carbon, dry matter, partitioning, root:shoot ratio, relative growth rate     

Effect of Light Intensity on Growth of Natural Populations of Dactylis glomerata L.

The growth of two natural populations of cocksfoot from contrastingclimatic regions, Norway and Portugal, was studied in two photoperiodsat three temperatures with three levels of light energy (48,144, and 240 W m^–2 in the wavelength interval 400–700nm). There was a consistent increase in relative growth-rate(RGR) in response to increased light energy up to 144 W m^–2,but above this energy level there was either no change, or,in some treatments, a decline. Net assimilation rate (NAR) increased,whilst leaf area ratio decreased from the lowest to the highestenergy level in most treatments. The decrease of LAR with increasedlight energy could be attributed to a decrease of both leafweight ratio (LWR) and specific leaf area (SLA), a greater proportionof dry matter being distributed to plant parts other than leaf.This effect occurred although there was a positive relationshipbetween light energy and relative leaf growth-rate (RLGR). Populationdifferences in these growth attributes were most marked in thetreatments with low-temperature and short-day conditions. Theefficiency of energy conversion of visible radiation declinedfrom 3–4 per cent at the lowest energy level to 1–2per cent at the highest energy level.