Physiological and Ecological Studies in the Analysis of Plant Environment: XIII. A Comparison of the Effects of Seasonal Variations in Light Energy and Temperature on the Growth of Helianthus annuus and Vicia faba in the Vegetative Phase

The influences of seasonal changes in light radiation and temperatureon the vegetative growth of Helianthus annuus and Vicia fabahave been investigated in the east of Scotland by pot experiments,carried out in the open at weekly intervals between June andSeptember in 1956 and May and October in 1957. To minimize theeffects of ontogenetic drift pots containing plants of a similarmorphological status were selected from batches sown every fewdays. At the beginning and end of each experiment replicatedand paired pots were harvested and the dry weights of the leaves,stems, and roots together with the leaf areas determined. Fromthese data weekly values for net assimilation rate, leaf-arearatio (ratio of leaf area to plant weight), and relative growthrate were calculated. Simultaneously, records were kept of the diurnal changes inair temperature and of light energy by means of an integratingphotometer. Multiple regressions linking light and temperature with netassimilation rate, leaf-area ratio, and relative growth ratewere calculated separately for each year. A significant ‘time-of-season’trend was largely eliminated by including an additional variable,the initial leaf-area ratio. In the individual regressions thevariance accounted for was very high, ranging from 75 to 97per cent. The results demonstrated that for both species the net assimilationrate and relative growth rate were positively dependent on lightand temperature. The leaf-area ratio of both species was negativelyaffected by light, but only for V. faba was there a positiverelationship between the leaf-area ratio and temperature. H.annuus grew faster than V. faba during the major part of theseason, largely because of its higher leaf-area ratio. The results are compared with prior investigations in Englandand elsewhere.     

Physiological and Ecological Studies in the Analysis of Plant Environment: X. An Analysis, of the Effects of Seasonal Variation in Daylight and Temperature on the Growth of Helianthus annuus in the Vegetative Phase

To determine on a quantitative and mathematical basis the effectsof seasonal changes in the levels of daylight and temperatureon vegetative growth and development in two years pot experimentsin the open were carried out at successive weekly intervalsbetween May and September. So as to minimize errors arisingfrom ontogenetic drifts the procedure adopted was to sow atintervals of a few days throughout the season batches of potswith seed of Helianthus annuus and to select pots containingplants of a standard morphological status for the start of eachweekly experiment. At the beginning and end of the week halfthe pots were harvested, the plants divided into root, stem,and leaf, the leaf area estimated, and the dry weights determined.The diurnal changes in air temperature were continuously recordedwhile the amount of daylight, excluding infra-red and ultravioletradiation, was measured with a specially constructed integratingrecorder. From the biological data for each week twelve variables werecalculated, namely the relative growth rates of both the wholeplant and the individual parts, the proportion by dry weightof the individual parts (root-, stem-, and leaf-weight ratios),the ratio of leaf area to total plant weight (leaf-area ratio),the rate of leaf expansion, the ratio of leaf area to leaf weight,and the net assimilation rate on the criteria of leaf area andweight. The main independent variables considered were the meanweekly temperature, the mean daily maximum minus the mean nightlyminimum temperature, the total amount of light per week, andthe time of year when the individual experiment was undertaken. Multiple regression analyses showed that (i) save for the stem-weightratio the data for the two years could be pooled, (ii) the fluctuationin diurnal temperature was of little account, (iii) transformationof the light data to either logarithms or square roots did notimprove the fit and (iv) for some of the dependent variables,e.g. leaf-area ratio, the ‘time of year’ effectwas significant but could be eliminated if the equation wasmodified to predict the value at the end of the week, giventhe initial value and the light and temperature data. The final series of multiple regressions revealed that (i) theleaf-weight ratio is not controlled by either the amount oflight or mean temperature, (ii) the relative growth rate ofthe root and the root-weight ratio are positively linked onlywith temperature, (iii) the rate of leaf growth either in areaor weight together with the net assimilation rate (area basis)are positively dependent on light alone, (iv) the net assimilationrate (weight basis) and the relative growth rates of the wholeplant and the stem are directly and positively correlated withboth temperature and light, and (v) the leaf-area ratio, theratio of leaf area to leaf weight and the stem-weight ratioare depressed by increasing light but augmented by rising temperature.In the individual regressions for net assimilation rate (areaand weight), the relative growth rates of the whole plant, stemand leaf weight, and the ratios of stem weight and leaf areato leaf weight the percentage variation accounted for rangedfrom 47 to as high as 91 per cent. The implication of these findings in relation to experimentsin controlled environmental chambers are discussed.     

Plant Growth Analysis: A Re-examination of the Methods of Calculation of Relative Growth and Net Assimilation Rates Without Using Fitted Functions

A method is proposed for estimating expected values of meanrelative growth and net assimilation rates, and their variances,over an interval of time, from replicated plant weight and leafarea data at each end of the time interval. The advantage ofthe method is that it avoids the necessity of pairing replicateplants at each of the two harvests, and gives exact resultsfor relative growth rate. The results for net assimilation rateare approximate, but the method proposed still avoids the pairingprocess which is regarded as an artificial necessity inherentin the conventional method. net assimilation rate, relative growth rate, mathematical analysis, Helianthus annuusL, sunflower, Triticum aestiuumL, wheat     

Comparative Growth of Triazine-susceptible and -resistant Biotypes ofSolanum nigrumat Different Light Levels

Effects of variation in light intensity on growth of plantsfrom five different populations of triazine-susceptible and-resistantSolanum nigrumwere studied in growth chambers at threelight levels. Plants were grown without intraspecific competitionand with optimal mineral nutrition. After 29 d, the mean biomassof resistant biotypes was about 25% less than that of susceptiblebiotypes at all light levels. Curve-fitting growth analysisshowed that this was the result of a lower initial biomass ofthe resistant biotype at the start of the experiment, as therelative growth rates (RGR) of the susceptible and resistantbiotypes in the early growth phase were equal. Specific leafarea (SLA) was higher for the resistant biotype but this wascompensated for by a lower net assimilation rate (NAR). Thefraction of dry matter invested in leaves was the same for bothbiotypes, but the resistant biotype produced more leaf areaper unit leaf weight. The equal RGR of the susceptible and resistantbiotypes in the early growth phase may have implications forthe competitive ability and population dynamics of a populationwith resistant biotypes.Copyright 1999 Annals of Botany Company Black nightshade, growth analysis, light level, management strategies, RGR, SLA,Solanum nigrum, triazine resistance, weed control.     

Differences in the Interacting Effects of Light and Temperature on Growth of Four Species in the Vegetative Phase

A comparative study, employing the concepts of growth analysis,has been made of the varying responses in the early vegetativephase of Gossypium hirsutum, Helianthus annuus, Phaseolus vulgaris,and Zea mays to combinations of light intensity (1.08, 2.16,3.24, 4.32, and 5.4 x 10⁴ lx—photoperiod 14 h) and constantdiurnal air temperatures (10, 15, 20, 25, 30, and 35 °C).Depending on the combination of treatments, the temperatureof the internal tissues departed from air temperature by 6.9to 1.4 °C: so only the internal temperatures are cited here. For each species there are complex interactions between theeffects of light and temperature on the net assimilation rate,the leaf-area ratio, and the relative growth-rates of plantweight and leaf area. The magnitude of the changes induced bythe two factors vary both with the growth component and thespecies. The temperature responses are maximal up to 20–5°C while at the highest temperatures they may be negative.The temperature coefficients for leaf-area ratio are consistentlyless than those of the other three components: here betweenspecies the coefficients over 10–20 °C vary by a factorof 9.6, 5.4, and 5.1 for the rates of gain in plant weight andleaf area and the net assimilation rate, while the orderingwithin each growth component is species dependent. Under conditions of optimal temperature the relative growth-rateand net assimilation rate progressively increase, accordingto the species, up to either 4.32 or 5.4x 10⁴ lx. The leaf-arearatio is always largest at the lowest intensity. The level oflight at which the rate of gain in leaf area reaches a maximumranges from 2.16x 10⁴ lx for Phaseolus to between 4.32 and 5.40x10⁴ lx for Gossypium. The highest relative growth-rate and net assimilation rate ofHelianthus exceed those of Zea substantially. Indeed the maximalassimilation rate for Helianthus of 2.10 g dm^–2 week^–1is the highest ever recorded under field or controlled conditions.Possible reasons for this reversal of the photosynthetic potentialsof the two species observed by previous workers are discussed.     

Physiological and Ecological Studies in the Analysis of Plant Environment: VII. An Analysis of the Differential Effects of Light Intensity on the Net Assimilation Rate, Leaf-Area Ratio, and Relative Growth Rate of Different Species

Since relative growth rate is the product of net assimilationrate and leaf-area ratio (leaf area/plant weight), it followsthat if the effects of shading on both net assimilation rateand leaf-area ratio can be expressed mathematically, then therelationship between light intensity and relative growth ratecan be derived from the product of the two mathematical expressions. For all the ten species investigated in field and pot cultureexperiments, it has been found that during the early vegetativephase both the changes in leaf-area ratio and net assimilationrate, over the range of 0·1 to full daylight, are linearlyrelated to the logarithm of the light intensity. In consequence,the relationship between relative growth rate and the logarithmof light intensity—being the product of the two linearregressions—is curvilinear. For species of shady habitats (Geum urbanum, Solamun dulcamara)neither the levels of assimilation rate nor the ‘compensation-point’values are very different from those of the eight species fromopen situations (e.g. Hordeum vulgare, Pisum sativum, Fagopyrumesculentum). Nevertheless the intensity at which growth rateis maximal varies between species: it is 0•5 for G. urbanum,0•7 for H. annuus, full daylight for F. esculentum, whilefor Trifolium subterraneum the calculated value is 1·8daylight. Such specific differences can be largely accountedfor in terms of the differences in leaf-area ratio at the differentlight levels. On the basis of this analysis of the light factor, a ‘shade’plant is best redefined as a species in which a reduction ofthe light intensity causes a rapid rise in the leaf-area ratiofrom an initial low value in full daylight: for a ‘sun’plant the converse definition holds.     

The Influences of Seasonal Changes in Solar Radiation and Air Temperature on the Growth in the Early Vegetative Phase of Zea mays

At weekly intervals from May to September over 2 years the growthof separate batches of Zea mays (Swiss hybrid Orla 266) wasrecorded for individual plants in pot experiments, togetherwith the corresponding weekly means of solar radiation and themean, maximum, and minimum diurnal air temperatures. To reducesampling errors the plants were ranked on the bases of initialgrain size and leaf number. To minimize differences in stageof development at the end of 21 days from sowing the size wasadjusted in 1965 by switching the pots in and out of a glasshouse:in 1966 the plants were kept for the first 11 days in a controlledenvironment and then hardened off in the open. Between 21 and28 days when the second sample was taken half the plants weresubjected to light shade (0.65–0.70 daylight). Multiple regression analysis showed that the relative growthrate of the whole plant (RGR), the rate of increase in leafarea (RLGR), and the net assimilation rate (NAR) were positivelydependent on both radiation and mean air temperature. In 1965there were negative effects of minimum temperature on RGR andNAR and a positive response of RLGR to leaf number. In 1966an increase in leaf number led to a higher RGR and LAR but depressedRLGR, while minimal temperature had no significant effects.In all these regressions the variation accounted for was high,ranging from 80 to 89 per cent. At the second sampling occasion the leaf-area ratio (LAR_f) wasinversely related to radiation, negatively dependent on daytemperature, but positively linked with night temperature. Theorder of the initial LAR exerted no influence. The RGRs of theshoot and the root were positively associated with both radiationand mean temperature. In 1965 there were small negative responsesof the shoot to both minimum temperature and leaf number andfor the root only leaf number. The variation accounted for wasleast for LAR_f (59–62 per cent) and intermediate for RGR_aand RGR_r (77–89 per cent). For RGR, NAR, and RLGR the calculated partial regression coefficientsfor mean temperature in 1965 were larger than those for radiationbut in 1966, apart from RLGR, they were equalled by radiation.The discrepancies between years can be ascribed to a highercorrelation coefficient between radiation and temperature in1965 (0.53) as against 1966 (0.33). The value of multiple regression analysis in the evaluationof the environment by carefully designed field experiments isemphasized in relation to other investigations of light andtemperature undertaken under controlled conditions.     

Effect of Temperature on Growth of Crotalaria juncea L. and Crotalaria sericea Retz.

Growth performances of Crotalaria juncea L. and C. sericea Retz.have been compared at two controlled temperatures, 16–20°C, and 28–32 °C, with respect to increase ind. wt and leaf area, relative growth rate, leaf area ratio,specific leaf area, leaf weight ratio, net assimilation rate,the ratio of mean relative growth rate to mean relative rateof leaf area increase () and shoot/root ratios. Both the speciesgrew better at the higher temperature; however the relativegrowth rate was more affected by temperature in C. sericea thanin C. juncea. Further, it was observed to be more dependenton net assimilation rate than on the leaf area ratio. Crotalaria juncea L., Crotalaria sericea Retz., relative growth rate, leaf area ratio, specific leaf area, leaf weight ratio, leaf area increase, net assimilation rate, shoot/root ratio     

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     

Humidity Pretreatment Affects the Responses of Stomata and CO2 Assimilation to Vapor Pressure Difference in C3 and C4 Plants

Experiments were carried out to investigate the long-term influenceof humidity on the short-term responses of stomata and CO₂ assimilationto vapor pressure difference in Oryza sativa (rice, C₃ species)and Panicum maximum (green panic, C₄ species). Plants were grownfor four weeks in growth chambers set at 35% and 85% relativehumidity at 25C air temperature, 38+2 Pa CO₂ partial pressureand 1,700µmol m^-2s^-1 photon flux density. Soil was saturatedwith water in both humidity treatments. Low humidity pretreatmentscaused low leaf conductance and low rates of transpiration andCO₂ assimilation in O. sativa, but small changes in stomatalresponses to humidity and in CO₂ assimilation were found inP. maximum. From the short-term gas exchange experiments, itwas noted that the responsiveness of leaf conductance to vaporpressure difference were affected by humidity pretreatmentsin O. sativa, whereas unaffected in P. maximum. In O. sativameasurements of CO₂ assimilation as a function of internal CO₂partial pressure (A-Ci curve) indicated that low humidity pretreatmentsreduced the CO₂ assimilation at high internal CO₂ partial pressure,but the initial slope of the A-Ci curve was unaffected. Furthermore,plant characteristics such as total dry weight and leaf areaof plants subjected to low umidity were lower than plants subjectedto high humidity. The reductions in O. sativa, however, werelarger than in P. maximum. Stomatal frequency from low humiditygrown plant was higher than that from high humidity grown plantsin both species although there is no significant difference.The data indicated that if the short term inhibition of netCO₂ assimilation at a high vapor pressure difference was imposedduring vegetative growth, the photosynthetic biochemistry andthe resultant plant growth were largely depressed in O. sativa,a C₃ species. (Received May 26, 1992; Accepted November 2, 1992)     

Some Effects of Alternating Temperature on the Growth of French Bean Plants

In the main experiment described plant dry weight and leaf area,relative growth-rate, net assimilation rate (on an area basis),leaf-weight ratio and leafarea ratio were studied for plantsgrown under a range of temperature régimes and in 12-hourdays. Comparisons under conditions where the mean temperaturewas the same showed that final dry weight and leaf area weregreatest at constant temperature and least where the temperaturefluctuated about the mean value. These findings are discussedin relation to the concept of thermoperiodism, and in relationto the significant effects of day and night temperature uponthe development of leaf area.     

Growth of Lettuce, Onion, and Red Beet. 1. Growth Analysis, Light Interception, and Radiation Use Efficiency

A field experiment was carried out to analyse the growth oflettuce, onion and red beet in terms of: (a) canopy architecture,radiation interception and absorption; (b) efficiency of conversionof absorbed radiation into biomass; and (c) dry matter partitioning.Growth analysis, total solar radiation interception, PAR interceptionand absorption by the crop canopy, ground cover, maintenancerespiration of onion bulbs and red beet storage roots were measured.Models for different leaf angle distribution and ground coverwere used to simulate light transmission by the crop canopy. The three crops are shown to have contrasting growth patternsfrom both a morphological and a physiological point of view.Lettuce showed very high light interception and growth afterthe early growth stages but, throughout the growth cycle, thisleafy crop showed the lowest radiation use efficiency due tothe respirational cost of the high leaf area. Onion showed alower early relative growth rate than lettuce and red beet.This was due partly to the low light interception per unit leafarea in the later stages of growth and partly to the low initialradiation use efficiency compared with the other two crops.On the other hand, thanks to more uniform distribution of theradiation inside the canopy, to the earlier termination of leafdevelopment and to the very low level of bulb respiration, onionshowed high radiation use efficiency and was able to producea large amount of dry matter. Red beet leaf posture and canopystructure resulted in high light interception and absorption.Its radiation use efficiency was lower than that of onion, partlyperhaps because of the more adverse distribution of the interceptedradiation fluxes within the canopy and partly because of thehigh respiration cost of a continuous dry-matter allocationto the leaves. However, this crop can accumulate a very largeamount of dry matter as leaf blade development and storage rootgrowth can both continue almost indefinitely, providing continuouslyavailable sinks. Ground cover gave a good estimate of the PAR interception onlyat low values of light interception but, in general, it underestimatedPAR interception in all three crops. Ratios between attenuationcoefficients established by considering PAR or total solar radiationand LAI or ground cover were calculated. Lettuce,Lactuca sativa L. var.crispa ; onion,Allium cepa L.; red beet; Beta vulgaris L. var.conditiva ; growth analysis; light interception and absorption; canopy architecture; ground cover; radiation use efficiency; maintenance respiration rate; dry matter distribution     

Growth Analysis of Sweet Pepper (Capsicum annuum L.): 2. Interacting Effects of Irradiance, Temperature and Plant Age in Controlled Conditions

A growth analysis was carried out with sweet pepper plants grownin a phytotron. Irradiance conditions were: 0.84 or 3.25 MJm^–2 in 8 h, 1.67 MJ m^–2 in 16 h and 2.51 MJ m^–2in 24 h. Temperatures applied were 25 or 21 °C during thephotoperiod in combination with 25, 21 and 17 or 21, 17 and13 °C respectively during the nyctoperiod. Highest values for leaf area and total dry weight were foundwhen applying 1.67 MJ m^–2 in 16 h, followed by 3.25 MJm^–2 in 8 h, irrespective of the temperature regime. Continuousirradiance ultimately resulted in leaf drop. A reduction inthe day temperature decreased leaf area and total dry weight.At a day temperature of 25 °C the dry weight increased withdecreasing night temperature when applying 3.25 MJ m^–2in 8 h. At a day temperature of 21 °C leaf area and dryweight were reduced when 17 or 13 °C were applied duringa 16 h nyctoperiod. Values for relative growth rate, net assimilation rate, leafarea ratio and leaf weight ratio strongly decreased with advancingplant age. The effects of irradiance treatment on RGR and NARwere analogous to those on total dry weight while the reversepattern was observed for the LAR. A decrease in day temperaturedecreased the RGR. The effects of night temperature exhibitedstrong interactions with day temperature and photoperiod. Theinfluence of temperature on RGR was largely mediated throughchanges in the LAR. The latter parameter was highly correlatedwith the specific leaf weight. Capsicum annuum L., sweet pepper, growth analysis, irradiance, temperature, plant age     

The Effects of Infection by Rust (Puccinia lagenophorae Cooke) on the Growth of Groundsel (Senecio vulgaris L.) Cultivated under a Range of Nutrient Concentrations

Groundsel (Senecio vulgaris L.), healthy or infected with therust fungus Puccinia lagenophorae Cooke, was grown at a rangeof nutrient concentrations in sand culture. There were statisticallysignificant interactions between the effects of infection andnutrient supply upon the dry weights of stems, leaves, rootsand reproductive tissues, leaf area and cumulative capitulumproduction. This interaction occurred since infection causedsignificant inhibitions of growth only at moderate or high nutrientconcentrations. At low concentrations rusted plants were similarto or slightly larger than controls. Both in controls and rustedplants root: shoot ratios increased as nutrient supply declined.The ratio of root: shoot dry weight was consistently reducedby infection whilst root length: leaf area ratio was relativelyunchanged. More detailed investigations confirmed that infection had littleeffect on plant growth under nutrient deficient conditions despitesuppression of the host's ability to increase root: shoot ratiosin response to nutrient stress. This reflected the inhibitionof relative growth rates in rusted plants at high but not lownutrient concentrations, which in turn reflected reduced netassimilation rates (NAR). Increases in leaf-area ratio (LAR)often ameliorated the decline in NAR in rusted plants. Senecio vulgaris L., Puccinia lagenophorae Cooke, nutrient deficiency, growth, root: shoot ratio     

Effects of Temperature and Leaf Position on Leaf Area Expansion of Kiwifruit (Actinidia deliciosa) Shoots: Development of a Modelling Framework

This paper describes mathematically the effects of temperatureand position on the expansion of leaves along a kiwifruit (Actinidiadeliciosa) shoot, taking into account shoot morphology. Theleaves were grouped into three zones along the shoot: initialcluster leaves (first zone); the rest of the leaves that werepreformed during the previous season (second zone); and leavesthat were initiated during the current season (third zone).After opening of the initial cluster, the leaves appeared atconstant rates for each of the two temperature treatments considered.The expansion of individual leaves was modelled by a growthfunction with the parameters: final area; duration of the growthwindow; centre of the growth window (timing of expansion); andlower asymptote. Within the first two zones, the pattern ofleaf expansion was affected by nodal position, with basal leaveshaving higher initial rates of expansion than distal leaves.The timing of expansion was linear with respect to the nodalposition within each of the zones, with the slope independentof temperature for the first zone. The slopes of the timingof expansion for the second and third zones depended on temperatureand were correlated for each temperature treatment. Final leafarea was a function of leaf position in the first zone and afunction of timing of leaf expansion for distal leaves startingfrom leaf 10. Temperature had no effect on final leaf area inthe first zone. For the rest of the leaves, temperature affectedfinal leaf area indirectly, through the timing of leaf expansion.The effect of temperature on the growth window of individualleaves within the first zone was less than that for the restof the leaves. However, simulated values for the total leafarea of shoots using the average shoot growth window showedgood agreement with experimental values.Copyright 2001 Annalsof Botany Company Actinidia deliciosa‘Hayward’, shoot development, individual leaf area, temperature effect, positional effects, modelling     

Growth Analysis of Sweet Pepper (Capsicum annuum L.): 1. The Influence of Irradiance and Temperature under Glasshouse Conditions in Winter

A growth analysis was carried out with sweet pepper grown ina glasshouse. The plants received natural daylight or additionalillumination applied either during or after the natural photopenod.All irradiance conditions were applied at three temperatureregimes. Additional illumination increased leaf number, leaf area andtotal dry weight. At all temperatures the long-day treatmentsshowed a smaller number of leaves, but a larger leaf area whencompared to the short-day treatments with the same daily radiationsum. A lower temperature progressively reduced leaf area. The derived growth analysis quantities showed strong ontogenetictrends. When comparing both methods of applying additional illuminationhigher mean relative growth rates were observed for the long-daytreatments, especially at the lowest temperature. No differencesin mean net assimilation rate were found, but the short-daytreatments showed a reduced mean leaf area ratio. A lower nighttemperature decreased RGR and NAR but did not affect LAR, alower day temperature increased NAR and decreased LAR. Changesin LAR were largely mediated by changes in specific leaf weight. Capsicum annuum L., sweet pepper, growth analysis, irradiance, temperature     

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

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

Leaf Characteristics and Net Gas Exchange of Diploid and Autotetraploid Citrus

The effect of tetraploidy on leaf characteristics and net gasexchange was studied in diploid (2x ) and autotetraploid (4x) ‘Valencia’ sweet orange (Citrus sinensis (L.)Osb.) and ‘Femminello’ lemon (Citrus limon (L.)Burm. f.) leaves. Comparisons between ploidy levels were madeunder high irradiance (I) in a growth chamber or low total Iin a glasshouse. Tetraploids of both species had thicker leaves,larger mesophyll cell volume and lower light transmittance thandiploids regardless of growth I. Mesophyll surface area perunit leaf area of 2x leaves was 5–15% greater than on4x leaves. Leaf thickness and mesophyll cell volume were greaterin high I leaves than low I leaves. In high I, average leafarea was similar for 2x and 4x leaves, whereas in low I it was30% greater in 4x than in 2x leaves. Nitrogen and chlorophyllconcentration per cell increased with ploidy level in both growthconditions. The ratio of chlorophyll a:b was 25% greater in2x than in 4x leaves. When net CO₂assimilation rate (A_CO2) wasbased on leaf area, 4x orange leaves had 24–35% lowerA_CO2than their diploids. There were no significant differencesin A_CO2between 2x and 4x orange or lemon leaves when expressedon a per cell basis. Overall, lower A_CO2per unit leaf area oftetraploids was related to increase in leaf thickness, largermesophyll cell volume, the decrease in mesophyll area exposedto internal air spaces, and the lower ratio between cell surfaceto cell volume. Such changes probably increased the resistanceto CO₂diffusion to the site of carboyxlation in the chloroplasts. Cell volume; chlorophyll; irradiance; leaf thickness; nitrogen; photosynthesis; ploidy; Citrus limon ; C. sinensis ; ‘Valencia’ sweet orange; ‘Femminello’ lemon     

Interacting Effects of Light and Day and Night Temperatures on the Growth of Four Species in the Vegetative Phase

A comparative examination has been made under controlled conditionsof the interacting effects on growth in the vegetative phasewhich takes place when the diurnal temperature is either maintainedconstant at 20 and 25 ?C or reduced at night by 5 and 10 ?Cand the plants subjected daily to either 2.16 or 4.32 ? 10⁴lx for 14 h. For each species (Gossypium hirsutum, Hclianthusannuus, Phaseolus vulgaris and Zea mays) the changes in netassimilation rate, the leaf area ratio and the relative growthrates in plant weight and leaf area were recorded. Contrary to some previous findings, none of these componentsof growth are favoured by cool nights. Rather such reductionsin temperature retard the growth processes to a varying degreeaccording to the species and the component. In general, significantreductions are more evident for the two relative growth rateswhen a drop from 20 to 10 ?C is combined with the lower levelof illumination. The implications of these results are considered in relationto a prior study where for similar light conditions the samespecies plants were subjected to constant temperatures rangingfrom 10 to 25 ?C.     

Photosynthesis, Dark Respiration and Bud Sugar Concentrations in Pepper Cultivars Differing in Susceptibility to Stress-induced Bud Abscission

Pepper (Capsicum annuum L.) cultivars differ in susceptibilityto stress-induced abscission. Previous research indicates thatthe stress susceptible cultivar 'Shamrock' undergoes a largerreduction in net assimilation rate (NAR) under low light stress,and partitions less dry matter (DM) to reproductive structuresand more to leaves than the more tolerant cultivar 'Ace'. Todetermine if photosynthetic rates under low light stress couldexplain NAR differences, photosynthesis was measured on 'Ace'and 'Shamrock'. Assimilate partitioning was compared throughmeasurement of leaf and bud respiration rates and analysis ofbud sugar concentrations. Photosynthetic rates per unit leafarea of leaves fully exposed to incident light revealed no cultivardifferences under low light conditions. Bud respiration ratesfell to a lower level in 'Shamrock' than 'Ace' in low light-stressedplants, while expanded leaves respired at higher rates in 'Shamrock'than 'Ace' under both full and low light. Bud sugar concentrationswere significantly lower in 'Shamrock' than 'Ace' after 3 dof low light stress. Susceptibility to low light stress-inducedabscission in 'Shamrock' appears to be associated with reducedassimilate partitioning to flower buds, which may be relatedto high assimilate consumption in maintenance of expanded leaves.Copyright1994, 1999 Academic Press Pepper (Capsicum annuum L.), abscission, low light stress, photosynthesis, respiration, sugars, assimilate partitioning, cultivar