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     

An Extension of the Logistic Model of Plant Growth

The kinetics of growth of Dactylis glomerata L. were studiedunder controlled temperature and nutritional conditions at threelevels of irradiance (35·55 and 85 W m^–s). Thedry weights of the root and shoot parts of the plants were measuredeach week between the fourth and eleventh weeks after sowing. The growth kinetics were found to be dependent on the levelof irradiance, but no significant differences in the root: totaldry weight ratio were observed. To characterize the effect of illuminance, the experimentalgrowth curves were analysed initially using the logistic model,the adequacy of which is discussed. An extension of the logisticmodel is proposed, represented by the kinetic equation dM/dt= kM, with < 1 and where M is the dry weight of the plant.It is shown that this relationship allows a distinction to bemade between two kinds of plant material according to theirfunctions in the growth process. Dactylis glomerata L., illuminance, growth curves, kinetic analyses, logistic model, shoot:root ratio, partition of assimilates     

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     

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     

Plant Growth Analysis: Allometry, Growth and Interference in Orchardgrass and Timothy

A multiple regression procedure was used to evaluate allometricresponses to stand age and species population densities in monoculturesand mixtures of orchardgrass (Dactylis glomerata L., also knownas cocksfoot) and timothy (Phleum pratense L.). In each speciesthe allometry between shoot dry weight and either leaf areaor tiller number per plant was studied. Population density treatmentsaffected allometry by changing allometric exponents expressingthe ratio of relative growth rates of different plant characteristics.Allometric relationships changed as growth proceeded, and thetwo species differed in their allometric responses to treatments. Plant growth analysis, allometry, competition, Dactylis glomerata L., Phleum pratense L.     

Relationship between Plant Weight and Growing Period for Vegetable Crops in the United Kingdom

A generalized equation is derived that relates total dry matterproduction to time from emergence for crops grown in the fieldwith adequate water and nutrients. It is: w+K₁lnw+W₀=K₂t where w is the plant dry weight in t ha^–1, t is time indays after emergence, K₂ and K₁ are constants and W₀ equals–(w₀+K₁lnw₀) where w₀ is the value of w at the start ofthe growing period. The increases in the dry matter of 18 different types of vegetablecrop were measured at intervals during growth in the field.In every case the data fitted the equation very satisfactorilywith K₁ set equal to 1 t ha^–1. The fitted values of K₂were similar for many crops; those of W₀ varied considerablybut were always similar to the values calculated from the individualseed weight and the plant population. Good fits were also obtainedwhen time in days was replaced with cumulative evaporation froman open water surface. It is concluded that the growth-time curves of many differentvegetable crops can be described by the same simple equationand that the variation between curves can be largely attributedto differences in seed weight and plant population.     

Is Partitioning of Dry Weight and Leaf Area Within Dactylis glomerata Affected by N and CO2Enrichment?

We examined changes in dry weight and leaf area within Dactylisglomerata L. plants using allometric analysis to determine whetherobserved patterns were truly affected by [CO₂] and N supplyor merely reflect ontogenetic drift. Plants were grown hydroponicallyat four concentrations of in controlled environment cabinets at ambient (360 µll^–1) or elevated (680 µl l^–1) atmospheric[CO₂]. Both CO₂and N enrichment stimulated net dry matter production.Allometric analyses revealed that [CO₂] did not affect partitioningof dry matter between shoot and root at high N supply. However,at low N supply there was a transient increase in dry matterpartitioning into the shoot at elevated compared to ambient[CO₂] during early stages of growth, which is inconsistent withpredictions based on optimal partitioning theory. In contrast,dry matter partitioning was affected by N supply throughoutontogeny, such that at low N supply dry matter was preferentiallyallocated to roots, which is in agreement with optimal partitioningtheory. Independent of N supply, atmospheric CO₂enrichment resultedin a reduction in leaf area ratio (LAR), solely due to a decreasein specific leaf area (SLA), when plants of the same age werecompared. However, [CO₂] did not affect allometric coefficientsrelating dry weight and leaf area, and effects of elevated [CO₂]on LAR and SLA were the result of an early, transient stimulationof whole plant and leaf dry weight, compared to leaf area production.We conclude that elevated [CO₂], in contrast to N supply, changesallocation patterns only transiently during early stages ofgrowth, if at all. Copyright 2000 Annals of Botany Company Allometric growth, carbon dioxide enrichment, Cocksfoot, Dactylis glomerata L., dry weight partitioning, leaf area ratio, nitrogen supply, shoot:root ratio, specific leaf area     

The Influence of Temperature on Photosynthesis and Transpiration in ten Temperate Grass Varieties Grown in four Different Environments

The influence of temperature on photosynthesis and transpirationwas studied in ten varieties of Lolium perenne, L. multiflorum,Dactylis glomerata, and Festuca arundinacea from three climaticorigins grown in three different controlled environments (15?C, 72 W m^-2 visible irradiation, 16-h photoperiod; 25 ?C, 72W m^-2 visible irradiation, 16-h photoperiod; and 25 ?C, 180W m^-2 visible irradiation, 16-h photoperiod) and in the glasshousein July/August. The optimum temperature for photosynthesis was influenced primarilyby growth environment; growth at low temperature (15 ?C) resultedin a low optimum temperature, which differed little from varietyto variety. The maximum CO₂-exchange rate was influenced bygrowth environment and by variety. Within a variety, plantsgrown at higher light intensity or lower temperature had a greaterCO₂-exchange rate. Seven varieties showed a negative correlationbetween the optimum leaf temperature and the maximum CO₂-exchangerate. Activation energies for photosynthesis were influencedby growth environment only. There were marked varietal differences in the values of leafresistances (r_a + r_t) obtained from transpiration data at theoptimum leaf temperature for CO₂ exchange. In Lolium, and Dactylisthe Mediterranean varieties had higher leaf resistances thanthe Northern varieties with the maritime varieties intermediate.In general the Dactylis varieties had higher resistances thanthe corresponding Lolium and Festuca varieties. Only at highgrowth temperatures was (r_a+r_l) insensitive to temperature;otherwise an activation energy of about 10 kcal/mole was observed.A negative correlation was found between mean varietal diffusionresistances (r_a+r_l), and corresponding maximum CO₂-exchangerates.     

Calcification in the Green Alga Halimeda: II. THE EXCHANGE OF CA2+ AND THE OCCURRENCE OF AGE GRADIENTS IN CALCIFICATION AND PHOTOSYNTHESIS

In Halimeda cylindracea and H. tuna segments, the concentrationof CaCO₃, MgCO₃, protein, and chlorophyll, as well as segmentvolume and wet and dry weight, increase with ‘age’i.e. from the apex of a branch downwards. Photosynthetic andcalcification rates decrease with age as does the degree oflight stimulation of calcification. Studies of the exchange of ⁴⁵Ca between the Halimeda thallusand the sea water under various conditions showed that mostof the Ca exchange is between the cell walls, the aragonitecrystals, and the intercellular space. The cell wall has twodistinguishable phases with half-times (t_0?5) of 200 and 35min while the CaCO₃ has a rapidly exchanging phase with a t_0?5of approximately 6 min. The t_0?5 of the exchange of Ca betweenthe intercellular space and the external medium is estimatedat about 6 min, on the basis of uptake studies. If the integrityof the barrier between the intercellular space and the externalsea water, created by the adpressed peripheral utricles is destroyedthe t_0?5 is smaller (<<3 min). These kinetic studies as well as comparative measurements ofcalcification rates by both isotopic and chemical methods showthat the ⁴⁵Ca method for measuring calcification rates overestimatesthe calcification rate, due to binding of ⁴⁵Ca in the cell wallsand retention of ⁴⁵Ca in the intercellular space. The ¹⁴C methodgives more accurate results and has the further advantage ofallowing simultaneous measurement of the photosynthetic andcalcification rate on the same segment.     

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     

Response to Temperature in a Stand of Pearl Millet: 10. PARTITION OF ASSIMILATE

Effects of temperature on partition of assimilate between leaves,stems and panicles of pearl millet are analysed in terms ofa duration (t_w) over which a structure increased in weight,and a partition factor (p)—the fraction of new dry matterallocated to the structure during t_w. The value of tw was, forall structures, inversely proportional to temperature abovea base of 10 °C and below an optimum of 28 to 30 °C.For stems and panicles, the value of p was, with one exception,little affected by temperature. The dry weight of these structureswas, therefore, proportional to t_w, and decreased with risein temperature. (The exception was panicles at the lowest temperature,19 °C, for which p was reduced by 40% because few grainswere set.) For leaves, however, p increased with rise in temperature,counteracting the effect on t_w, such that dry weight changedlittle with temperature. The optimum temperature for reproductiveyield was 22 °C, but the proportion of the total dry matterallocated to reproductive structures changed little between22 °C and 31 °C. Key words: Pearl millet, temperature, thermal time, partitioning     

A model for phosphocreatine resynthesis

Nevill, Alan M., David A. Jones, David McIntyre, Gregory C. Bogdanis, and Mary E. Nevill. A model forphosphocreatine resynthesis. J. Appl.Physiol. 82(1): 329-335, 1997.A model for phosphocreatine (PCr) resynthesis is proposed based on a simple electric circuit, where the PCr store in muscle is likened to thestored charge on the capacitor. The solution to the second-order differential equation that describes the potential around the circuitsuggests the model for PCr resynthesis is given byPCr(t) = R  [d₁ ^· exp(k₁ ^· t) ± d₂ ^· exp(k₂ ^· t)],where R is PCr concentration at rest,d₁,d₂, k₁, andk₂ are constants, andt is time. By using nonlinear leastsquares regression, this double-exponential model was shown to fit thePCr recovery data taken from two studies involving maximal exerciseaccurately. In study 1, when themuscle was electrically stimulated while occluded, PCr concentrations rose during the recovery phase to a level above that observed at rest.In study 2, after intensive dynamicexercise, PCr recovered monotonically to resting concentrations. Thesecond exponential term in the double-exponential model was found tomake a significant additional contribution to the quality of fit inboth study 1 (P < 0.05) andstudy 2 (P < 0.01).

     

Comparison of carbon-specific growth rates and rates of cellular increase of phytoplankton in large limnetic enclosures

Potential carbon-specific growth rates of phytoplankton wereestimated from a series of measurements of photosynthetic radio-carbonuptake over 4- and 24-h exposure periods in the light fieldsof three large limnetic enclosures (‘Lund Tubes’),each providing different limnological and trophic conditions.Photosynthetic behaviour and short-term, chlorophyll-specificcarbon-fixation rates conformed to well-established criteriabut, over 24 h, the net retention represented 23–82% ofthe carbon fixed during the daylight hours. Potential mean growthrates (k'_p, of the photo-autotrophic community were calculatedas the net exponential rates of daily carbon-accumulation relativeto derived, instantaneous estimates of the cell carbon-content.Apparent actual community growth rates (k'_D were calculatedas the sum of the exponential rates of change of each of themajor species present, corrected for probable rates of in situgrazing and sinking, and expressed relative to the fractionof total biomass for which they accounted. The correspondingvalues were only occasionally similar, k'_p generally exceedingK'_D by a factor of between 1 and 30 or 1 and 14, depending uponthe carbon:chlorophyll ratio used. The ratio, K'_p/K'_D was foundto vary inversely both to k'_D and to k_n, the net rate of changein phytoplankton biomass, suggesting that measured carbon fixationrates merely represent a capacity for cellular increase which,owing to other likely limitations upon growth, is seldom realized.Apparent rates of loss of whole cells do not account for theloss of carbon; that the ‘unaccounted’ loss rates(K'_p–K'_D varied in direct proportion to K'_p (i.e., losseswere least when chlorophyll-specific photosynthetic productivitywas itself limited) is best explained by physiological voidingof excess carbon (for instance, by respiration, photorespiration,excretion) prior to the formation of new cells.     

Use of the Expolinear Growth Model to Analyse the Growth of Faba bean, Peas and Lentils at Three Densities: Fitting the Model

The expolinear equation for crop growth (Goudriaan and MonteithAnnalsof Botany66: 695–701, 1990) was fitted to measurementsof above ground dry weight made on two cultivars of each ofthree species, faba bean (Vicia fabaL.), peas (Pisum sativumL.)and lentils (Lens culinarsMedic.), each grown at three densitiesat the University of Reading, UK in 1992 and 1993. The expolinearequation fitted the data well but required frequent samplingto obtain good estimates of the parameters. The equation hasthree parameters,R_mthe maximum relative growth rate,C_ma maximumcrop growth rate, andt_bthe time at which the crop effectivelyreaches a linear phase of growth.R_mdid not differ between densities,cultivars or species but differed between years.C_mincreasedwith increased density and was lower for lentils than for fababeans or peas.t_bdecreased with increased density for faba beanbut not for the other species. Incorporating an extinction coefficientfor solar radiation and the maximum fraction of radiation interceptedenabled reasonably accurate time courses of leaf area indexto be derived, as suggested by Goudriaan (1994. In: MontiethJL, Scott RK, Unsworth MH, eds.Resource capture by crops. Nottingham:Nottingham University Press, 99–110).Copyright 1998 Annalsof Botany Company Expolinear equation, grain legumes, crop growth rate, crop density, relative growth rate, growth modelling, faba bean,Vicia fabaL., peas,Pisum sativumL., lentils,Lens culinarsMedic.     

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 Partitioning of Nitrate Assimilation Between Root and Shoot of a Range of Temperate Cereals and Pasture Grasses

Nitrate reductase activity (NRA, in vivo assay) and nitrate(NO^-₃) content of root and shoot and NO^-₃ and reduced nitrogencontent of xylem sap were measured in five temperate cerealssupplied with a range of NO^-₃ concentrations (0·1–20mol m^–3) and three temperate pasture grasses suppliedwith 0·5 or 5 0 mol m^–3 NO^-₃ For one cereal (Hordeumvulgare L ), in vitro NRA was also determined The effect ofexternal NO^-₃ concentration on the partitioning of NO^-₃ assimilationbetween root and shoot was assessed All measurements indicatedthat the root was the major site of NO3 assimilation in Avenasatwa L, Hordeum vulgare L, Secale cereale L, Tnticum aestivumL and x Triticosecale Wittm supplied with 0·1 to 1·0mol m^–3 NO^-₃ and that for all cereals, shoot assimilationincreased in importance as applied NO^-₃ concentration increasedfrom 1.0 to 20 mol m^–3 At 5.0–20 mol m^–3 NO3,the data indicated that the shoot played an important if notmajor role in NO^-₃ assimilation in all cereals studied Measurementson Lolium multiflorum Lam and L perenne L indicated that theroot was the main site of NO^-₃ assimilation at 0.5 mol m^–3NO^-₃ but shoot assimilation was predominant at 5.0 mol m^–3NO^-₃ Both NRA distribution data and xylem sap analysis indicatedthat shoot assimilation was predominant in Dactylis glomerataL supplied with 0.5 or 5.0 mol m^–3 NO^-₃ Avena sativa L., oats, Hordeum vulgare L., barley, Secale cereale L., rye, x Triticosecale Wittm., triticale, Triticum aestivum L., wheat, Dactylis glomerata L., cocksfoot, Lolium multiflorum Lam., Italian ryegrass, Lolium perenne L., perennial ryegrass, nitrate, nitrate assimilation, nitrate reductase activity, xylem sap     

Maintenance Respiration and Carbon Balance of Plants at Low Levels of Sodium Chloride Salinity

The daily course of carbon influx and efflux was measured inyoung plants of Phaseolus vulgaris, Xanthium strumarium, Zeamays, and Atriplex halimus, exposed to low levels of salinity(NaCl) and varying daytime light intensities. Maintenance respiration(R_M) was calculated. In Phaseolus, Xanthium, and Atriplex, R_Mrose with increasing salinity, approximately up to those levelsof salinity above which apparent signs of toxicity appear. Athigher levels of salinity R_M declined. There was no responseof R_M to salinity in Zea. At the levels of salinity tested,salinity did not affect the ratio of growth respiration to photosynthesis. At –5 x 10⁵ Pa of NaCl salinity, the increase in R_M inXanthium was calculated to account for 24% of the growth reductioncaused by salt. The remainder could be ascribed to reduced photosynthesis.The increase of R_M is considered to be indicative of an adaptivemechanism, not present in the very salt-sensitive Zea.     

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.