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1.
Gas exchange measurements were undertaken on 2-year-old plantsof Clusia rosea. The plants were shown to have the ability toswitch from C3-photosynthesis to CAM and vice versa regardlessof leaf age and, under some conditions, CO2 was taken up continuously,throughout the day and night. The light response was saturatedby 120 µmol m–2 s–1 typical of a shade plant. Gas exchange patterns in response to light, water and VPD wereexamined. All combinations of daytime and night-time CO2 uptakewere observed, with rates of CO2 uptake ranging from 2 to 11µmol m–2 s–1 depending upon water status andlight. Categorization of this plant asC3, CAM or an intermediateis impossible. Differing VPD affected the magnitude of changesfrom CAM to C3-photosynthesis (0 to 0.5 and 0 to 6.0 µmolm–2 s–1 CO2, respectively) when plants were watered.Under well-watered conditions, but not under water stress, highPPFD elicited changes from CAM to C3 gas exchange. This is unusualnot only for a shade plant but also for a plant with CAM. Itis of ecological importance for C. rosea, which may spend theearly years of its life as an epiphyte or in the forest understorey,to be able to maximize photosynthesis with minimal water loss. Key words: Clusia rosea, CAM, C3, stress  相似文献   

2.
Permeability coefficients (PS values) for CO2 of the plasmamembrane (PM) of the unicellular green algae Eremosphaera viridis,Dunaliella parva, and Dunaliella acidophila, and of mesophyllprotoplasts isolated from Valerianella locusta were determinedfrom 14CO2 uptake experiments using the rapid separation ofcells by the silicone oil layer centrifugation technique. Theexperimental PS values were compared with calculated numbersobtained by interpolation of Collander plots, which are basedon lipid solubility and molecular size, for D. parva cells,mesophyll protoplasts isolated from Spinacia oleracea, mesophyllcells and guard cells of Valerianella, and guard cell protoplastsisolated from Vicia faba. The conductivity of algal plasma membranes for CO2 varies between0.1 and 9 ? 10–6 m s–1, whereas for the plasmalemmaof cells and protoplasts isolated from leaves of higher plantsvalues between 0.3 and 11 ? 10–6 m s–1 were measured.By assuming that these measurements are representative for plantsand algae in general, it is concluded that the CO2 conductivityof algal PM is of the same order of magnitude as that of thehigher plant cell PM. Ps values of plasma membranes for CO2are lower than those for SO2, but are in the same order of magnitudeas those measured for H2O. On the basis of these results itis concluded that theoretical values of about 3000 ? 10–6m s–1 believed to be representative for higher plant cells(Nobel, 1983) and which are frequently used for computer-basedmodels of photosynthesis, lack experimental confirmation andrepresent considerable overestimations. However, with severalsystems, including higher plant cells, the conductance of thePM for CO2 was significantly higher in light than in darkness.This suggests that in light, additional mechanisms for CO2 uptakesuch as facilitated diffusion or active uptake may operate inparallel with diffusional uptake. Key words: Conductivity, CO2, permeability coefficient, photosynthesis, plasmalemma  相似文献   

3.
In studies of Trifolium repens nitrogen nutrition, the controlof nutrient solution pH using dipolar buffers, was evaluatedin tube culture under sterile conditions. Five buffers; MES,ADA, ACES, BES and MOPS with pK2s (20 °C) of 6.15, 6.60,6.90, 7.15 and 7.20 respectively, at a concentration of 2.0mol m–3, were provided to inoculated Trifolium repensgrowing in nutrient solution containing 7.13 mol m–3 nitrogenas (NH4)2SO4. Initial pH of each solution was adjusted to theappropriate buffer pK2 Two buffers, ADA and ACES completelyinhibited plant growth. The remaining buffers had little effectin limiting pH change, although plant dry matter was higherand nodule numbers lower in the presence of these buffers. MESand MOPS were supplied to nutrient solutions with and without7.13 mol m–3 (NH4)2SO4, at concentrations ranging from0–12 mol m–3. MES at 9 mol m–3 and 12 molm–3 reduced growth of plants reliant on the symbiosisfor providing nitrogen. The provision of MES to plants providedwith NH4+ significantly increased plant yield and reduced nodulenumber at all concentrations. MOPS did not affect plant yieldor nodule number. The use of dipolar buffers in legume nitrogennutrition studies is considered in terms of buffering capacity,and the side effects on plant growth and symbiotic development. Key words: Ammonium, Dipolar buffer, Nitrogen nutrition, pH control, Symbiosis, Trifolium repens  相似文献   

4.
Acclimation of Lolium temulentum to enhanced carbon dioxide concentration   总被引:2,自引:0,他引:2  
Acclimation of single plants of Lolium temulentum to changing[CO2] was studied on plants grown in controlled environmentsat 20°C with an 8 h photoperiod. In the first experimentplants were grown at 135 µ;mol m–2 s–1 photosyntheticphoton flux density (PPFD) at 415µl l–1 or 550µll–1 [CO2] with some plants transferred from the lowerto the higher [CO2] at emergence of leaf 4. In the second experimentplants were grown at 135 and 500 µmol m–2 s–1PPFD at 345 and 575 µl l–1 [CO2]. High [CO2] during growth had little effect on stomatal density,total soluble proteins, chlorophyll a content, amount of Rubiscoor cytochrome f. However, increasing [CO2] during measurementincreased photosynthetic rates, particularly in high light.Plants grown in the higher [CO2] had greater leaf extension,leaf and plant growth rates in low but not in high light. Theresults are discussed in relation to the limitation of growthby sink capacity and the modifications in the plant which allowthe storage of extra assimilates at high [CO2]. Key words: Lolium, carbon dioxide, photosynthesis, growth, stomatal density  相似文献   

5.
Connelly, A., Lohman, J. A. B., Loughman, B. C., Quiquampoix,H. and Ratcliffe, R. G. 1987. High resolution imaging of planttissues by NMR.—J. exp. Bot. 38: 1713–1723. NMR images of living plant tissues were recorded at a 1H frequencyof 200 MHz using a high resolution imaging technique that gavean in-plane pixel resolution of 50 µm x 50 µm orbetter. Images with interpretable contrast were obtained fromgerminating seeds, the roots of seedlings and the stems of youngplants. The expected structural features of these tissues werereadily observed including, in Mn2+ loaded tissue, the xylemvessels of maize root sections. Preliminary experiments on H2O-D2Oexchange in maize roots, on the uptake of Mn2+ by maize rootsand on the germination of seeds in situ demonstrate that thenon-invasive method of NMR mini-imaging has the potential tocomplement existing techniques for physiological investigationsin plant tissues. Key words: NMR imaging, water content, ion uptake  相似文献   

6.
The effects of three ranges of CO2 concentration on growth,carbon distribution and loss of carbon from the roots of maizegrown for 14 d and 28 d with shoots in constant specific activity14CO2 are described. Increasing concentrations of CO2 led toenhancement of plant growth with the relative growth rate (RGR)of the roots affected more than the RGR of the shoots. Between16% and 21% of total net fixed carbon (defined as 14C retainedin the plant plus 14C lost from the root) was lost from theroots at all CO2 concentrations at all times but the amountsof carbon lost per unit weight of plant decreased with time.Possible mechanisms to account for these observations are discussed. Key words: Growth, Roots, Carbon loss, [CO2]  相似文献   

7.
Leaves of three C4 plants, Setaria italica, Pennisetum typhoides,and Amaranthus paniculatus possessed five- to ten-fold higheractivities of a (Na+-K+)-dependent ATPase than those of twoC3 plants, Oryza sativa and Rumex vesicarius. Na+-K+ ATPasefrom leaves of Amarathus exhibited an optimal pH of 7?5 andan optimal temperature of 35 ?C. It required 40 mM K+ and 80mM Na+ for maximal activity. Ouabain partially inhibited (Na+-K+)-dependentATPase activity in leaves of C4 plants. Ouabain also blockedthe movement of label from initially formed C4 acids into endproducts in leaves of only C4 plants, Setaria and Amaranthusbut not in a C3 plant, Rumex. We propose that Na+-K+ ATPasemay mediate transfer of energy during active transport of C4acids from mesophyll into the bundle sheath.  相似文献   

8.
Photosynthetic carbon metabolism was studied with Chroomonassp. cells in which the rate of photosynthesis was inhibitedunder both an anaerobic condition and high concentrations ofoxygen. The time course of 14C-incorporation into photosyntheticproducts showed that 3-phosphoglycerate was the initial productof photosynthetic CO2 fixation in Chroomonas sp. cells. During5-min photosynthesis, a considerable amount of 14C was incorporatedinto the insoluble fraction (mostly cryptomonad starch), andoxygen predominantly affected 14C-incorporation into this fraction.Although 14C-incorporation into intermediates of the photorespiratorypathway increased with increasing O2 concentration, the amountswere much less than expected from the degree of oxygen inhibition.It is noteworthy that 14C-dihydroxyacetone phosphate accumulatedduring photosynthesis only under the anaerobic condition, whereasthe levels of the other phosphate esters were scarcely affectedby the oxygen concentration. Ribulose-1,5-bisphosphate carboxylase from Chroomonas sp. wascompetitively inhibited by oxygen, and its Km(CO2) value wassimilar to those of terrestrial C3 plant enzymes. (Received November 19, 1984; Accepted May 20, 1985)  相似文献   

9.
Net photosynthetic rates per unit ground area for plant standsof Solanum melongena L. var. esculentum (aubergine) and Amaranthuscaudatus L. var. edulis (grain amaranth) were measured over10 min intervals in an airtight, glass, controlled-environmentcabinet for a range of light flux densities provided by thediurnal variation in daylight. Light response curves for photosynthesisof stands, grown at ambient CO2 concentration, were definedat 400, 800 and 1200 vpm CO2. Light compensation points for these stands were around 20-30J m-2 s-1 and decreased slightly at higher CO2 concentrations.For aubergine, a C3 species, the short-term effects of CO2 enrichmentwere to increase the initial slope as well as the asymptoteof the light response curve, reducing light saturation at moderateto high light flux densities; but for amaranthus, a C4 species,saturation was less apparent and CO2 enrichment scarcely increasedphotosynthesis except at light flux densities above 150 J m-2s-1. The canopies intercepted 93-98% of incident light. The efficiencyof utilization of intercepted light in photosynthesis (µgCO2 J-1) increased from zero at the light compensation pointto a maximum at an optimum light flux density of about 100 Jm-2 s-1 (the optimum rose a little with CO2 enrichment) anddecreased slightly with further increase in light. Maximum utilizationefficiencies at 400 vpm CO2 were 8-9 µg CO2 J-1. Enrichmentto 1200 vpm did not affect the peak utilization efficiency ofthe C4 amaranthus, but increased that aubergine to 12·2µg CO2 J-1 (equivalent to some 14% when using the heatof combustion of plant dry matter to convert to the dimensionlessform). This is among the highest recorded efficiencies of lightutilization for stands, and relates to the exceptionally favourableenvironment, with optimal control of CO2 concentration, humidity,temperature, water supply and mineral nutrition.Copyright 1993,1999 Academic Press Amaranthus caudatus L. var. edulis, Solanum melongena L. var. esculentum, canopy photosynthesis, CO2 enrichment, light interception, light utilization, photosynthetic efficiency  相似文献   

10.
Twenty-four hours after leaf 3 of a plant of Lolium multiflorumLam, was supplied with a droplet of 14C-urea and the plant enclosedin a polyethylene bag with an untreated plant, there were significantamounts of radiocarbon recovered from the untreated plant. Theleaf treated with 14C-urea was the major source of 14C leakagebut significant losses were also recorded from other parts ofthe plant. Reducing the humidity within the bag decreased theamount of 14CO2 which escaped. Losses of radiocarbon from CO2-treated plants were very low compared with those from urea-treatedplants but the pattern of assimilate distribution within thetwo types of plants was very similar. The possible causes ofthese effects are considered and the usefulness of 14C-ureaas a source of 14CO2 discussed.  相似文献   

11.
The occurrence and endogenous level of various plant hormoneswere measured for the short-day plants Lemna paucicostata 151and 381 and the long-day plant Lemna gibba G3 to determine whetherany of them are involved in the photoperiodic control of flowering.ABA, IAA, GA1, GA29, GA34, GA53, trans- and cis-zeatin, trans-and cis-ribosyl zeatin, N6-(2-isopentenyl) adenine and N6-(2-isopentenyl)adenosine were definitely detected in each species, while GA4was only detected in L. gibba G3 and GA20 was only detectedin L. paucicostata 151. The endogenous levels of ABA and IAAwere in the range of 1–7 ng/g fr wt and were not significantlydifferent in vegetative and flowering plants. The endogenousgibberellin levels were generally higher in Lemna grown underlong-day rather than short-day conditions. The endogenous cytokininlevels were almost the same in both flowering and vegetativeplants of L. paucicostata 151 and 381. In L. gibba G3, however,the level of cis-ribosyl zeatin, N6-(2-isopentenyl) adenineand N6-(2-sopentenyl) adenosine were higher in vegetative thanin flowering plants. These results indicate that there is not necessarily a directrelation between endogenous plant hormone levels and flowering,and that the chemical basis for the photoperiodic control offlowering cannot be explained solely by changes in hormone levels.The possibility remains, however, that one or more of the planthormones has some influence of secondary importance on the floweringprocess in Lemna. (Received January 29, 1986; Accepted July 12, 1986)  相似文献   

12.
Mesophyll chloroplasts were isolated from leaves of a Na+-requiringNAD-malic enzyme type, dicotyledonous C4 plant, Amaranthus tricolorL. The chloroplasts converted pyruvate to phosphoenolpyruvateunder illumination, and the conversion was stimulated by Na+.This observation may explain the requirement for Na+ of someC4 plants. 2 Present address: Institute for Life Science Research, NihonNohyaku Co., Ltd., Kawachi-Nagano, Osaka, 586 Japan  相似文献   

13.
Experiments were conducted during the 1974–75 and 1975–76winter season with the barley (Hordeum vulgare L.) cultivarJyoti. From amongst the various plant parts, the flag leaf bladehad higher in vivo nitrate reductase (NR) activity than thelower two leaf blades, glumes, and grains. However, the potentialof a plant part to reduce NO3 is a function of its freshweight and the NR per unit fresh weight. On this basis, thesecond and third leaf blades could reduce more NO3 thanthe flag leaf blade. N fertilizer application resulted in enhancementof the activity of the leaf blades alone. N fertilizer appliedduring the reproductive phase was taken up and assimilated bythe various plant parts. The studies suggest that, even whenthe fertilizer is applied at optimum levels for obtaining maximumyields, the upper leaf blades have sub-optimal NR activity andthat there is a likelihood of either a preferential flow ofNO3 to the leaf blades or transnational barriers to NO3movement to the ear.  相似文献   

14.
The influence of varying light intensity and quality on thecarbon labelling patterns in Rumex vesicarius (a C3 plant),Setaria italica (a malate-formingC4 plant), and Amaranthus paniculatus(an aspartate-forming C4 plant) was studied. In A. paniculatusand B. vesicarius blue light decreased the transfer of radioactivityto sugars and starch but in S. italica only slightly decreasedradioactivity in sugar phosphates, sucrose, and insolubles.Negligible transfer was observed from the C4 acids to sugarphosphates, sucrose, and starch under dim blue-green and blue-yellowlights in S. italica and A. paniculatus. Blue light favouredthe formation of malate, aspartate, and alanine in all threeplants. The differential effect of blue and red light suggesteda variation in the mechanisms of C4-photosynthesis in Setariaand Amaranthus. Leaves of S. italica and A. paniculatus were allowed to photosynthesizein 14CO2 for 5 s and then the distribution of the labelled productsbetween the mesophyll and the bundle sheath cells was determinedduring subsequent photosynthesis in 12CO2. Malate and aspartatewhich appeared initially in the mesophyll layer moved rapidlyinto the bundle sheath cells. Phosphoglyceric acid originatingin the bundle sheath moved swiftly to the mesophyll layer. Sugarphosphates were recovered from both the mesophyll and the bundlesheath cells. Most of the starch was found in the bundle sheathcells while sucrose and alanine were localized in the mesophyllcells.  相似文献   

15.
The rate of net photosynthesis (P) of whole plant stands oftomato (Lycopersicon esculentum Mill.), cucumber (Cucumis sativusL.) and sweet pepper (Capsicum annuum L.) was measured in sixlong-term experiments in large greenhouses under normal operatingconditions and CO2-concentrations between 200 and 1200 µmolmol-1. The objective was to quantify the responses to lightand carbon dioxide and to obtain data sets for testing simulationmodels. The method of measuring canopy photosynthesis involvedan accurate estimation of the greenhouse CO2 balance, usingnitrous oxide (N2O) as tracer gas to determine, on-line, theexchange rate between greenhouse and outside air. The estimatedrelative error in the observed P was about ± 10%, exceptthat higher relative errors could occur under particular conditions. A regression equation relating P to the photosynthetically activeradiation, the CO2 concentration and the leaf area index explained83-91% of the variance. The main canopy photosynthesis characteristicscalculated with the fitted regression equations were: canopyPmax 5-9 g m-2 h-1 CO2 uptake; ratio Pmax/LAI 1·5-3 gm-2 h-1; light compensation point 32-86 µmol s-1 m-2;light use efficiency (quantum yield) at low light 0·06-0·10µmol µmol-1 and CO2 compensation point 18-54 µmolmol-1. The results were related to the prevailing conditions.Copyright1994, 1999 Academic Press Canopy photosynthesis, Capsicum annuum L., carbon dioxide, CO2, CO2 balance, CO2 use efficiency, cucumber, Cucumis sativus L., glasshouse, greenhouse, light use efficiency, Lycopersicon esculentum Mill., sweet pepper, tomato, tracer gas  相似文献   

16.
Species-specific differences in the assimilation of atmosphericCO2 depends upon differences in the capacities for the biochemicalreactions that regulate the gas-exchange process. Quantifyingthese differences for more than a few species, however, hasproven difficult. Therefore, to understand better how speciesdiffer in their capacity for CO2 assimilation, a widely usedmodel, capable of partitioning limitations to the activity ofribulose-1,5-bisphosphate carboxylase-oxygenase, to the rateof ribulose 1,5-bisphosphate regeneration via electron transport,and to the rate of triose phosphate utilization was used toanalyse 164 previously published A/Ci, curves for 109 C3 plantspecies. Based on this analysis, the maximum rate of carboxylation,Vcmax, ranged from 6µmol m–2 s–1 for the coniferousspecies Picea abies to 194µmol m–2 s–1 forthe agricultural species Beta vulgaris, and averaged 64µmolm–2 s–1 across all species. The maximum rate ofelectron transport, Jmax, ranged from 17µmol m–2s–1 again for Picea abies to 372µmol m–2 s–1for the desert annual Malvastrum rotundifolium, and averaged134µmol m–2 s–1 across all species. A strongpositive correlation between Vcmax and Jmax indicated that theassimilation of CO2 was regulated in a co-ordinated manner bythese two component processes. Of the A/Ci curves analysed,23 showed either an insensitivity or reversed-sensitivity toincreasing CO2 concentration, indicating that CO2 assimilationwas limited by the utilization of triose phosphates. The rateof triose phosphate utilization ranged from 4·9 µmolm–2 s–1 for the tropical perennial Tabebuia roseato 20·1 µmol m–2 s–1 for the weedyannual Xanthium strumarium, and averaged 10·1 µmolm–2 s–1 across all species. Despite what at first glance would appear to be a wide rangeof estimates for the biochemical capacities that regulate CO2assimilation, separating these species-specific results intothose of broad plant categories revealed that Vcmax and Jmaxwere in general higher for herbaceous annuals than they werefor woody perennials. For annuals, Vcmax and Jmax averaged 75and 154 µmol m–2 s–1, while for perennialsthese same two parameters averaged only 44 and 97 µmolm2 s–1, respectively. Although these differencesbetween groups may be coincidental, such an observation pointsto differences between annuals and perennials in either theavailability or allocation of resources to the gas-exchangeprocess. Key words: A/Ci curve, CO2 assimilation, internal CO2 partial pressure, photosynthesis  相似文献   

17.
Upland grasslands are a major component of natural vegetationwithin the UK. Such grasslands support slow growing relativelystable plant communities. The response of native montane grassspecies to elevated atmospheric carbon dioxide concentrationshas received little attention to date. Of such studies, mosthave only focused on short-term (days to weeks) responses, oftenunder favourable controlled environment conditions. In thisstudy Agrostis caplllaris L.5, Festuca vivipara L. and Poa alpinaL. were grown under semi-natural conditions in outdoor open-topchambers at either ambient (340µmol mol–1) or elevated(680µmol mol–1) concentrations of atmospheric carbondioxide (CO2 for periods from 79 to 189 d, with a nutrient availabilitysimilar to that of montane Agrostis-Fescue grassland in Snowdonia,N. Wales. Whole plant dry weight was increased for A. capillarisand P. alpina, but decreased for F. vivipara, at elevated CO2.Major components of relative growth rate (RGR) contributingto this change at elevated CO2 were transient changes in specificleaf area (SLA) and leaf area ratio (LAR). Despite changes ingrowth rate at 680 µmol mol–1 CO2, partitioningof dry weight between shoot and root in plants of A. capillarisand P. alpina was unaltered. There was a significant decreasein shoot relative to root growth at elevated CO2 in F. viviparawhich also showed marked discoloration of the leaves and increasedsenescence of the foliage. Key words: Allometry, growth analysis, elevated CO2, grasses  相似文献   

18.
Two approaches to quantifying relationships between nutrientsupply and plant growth were compared with respect to growth,partitioning, uptake and assimilation of NO3 by non-nodulatedpea (Pisum sativum L. cv. Marma). Plants grown in flowing solutionculture were supplied with NO3 at relative addition rates(RAR) of 0·03, 0·06, 0·12, and 0·18d–1, or constant external concentrations ([NO3)of 3, 10, 20, and 100 mmol m–3 over 19 d. Following acclimation,relative growth rates (RGR)approached the corresponding RARbetween 0·03–0.12 d-1, although growth was notlimited by N supply at RAR =0.18 d-1. Growth rates showed littlechange with [NO3–] between 10–100 mmol m–3(RGR=0·15 –0·16 d-1). The absence of growthlimitation over this range was suggested by high unit absorptionrates of NO3, accumulation of NO3 in tissues andprogressive increases in shoot: root ratio. Rates of net uptakeof NO3 from 1 mol m–3 solutions were assessed relativeto the growth-related requirement for NO3, showing thatthe relative uptake capacity increased with RGR between 0·03–0·06d–1 , but decreased thereafter to a theoretical minimumvalue at RGR  相似文献   

19.
The growth of four heathland species, two grasses (D. flexuosa,M. caerulea) and two dwarf shrubs (C. vulgaris, E. tetralix),was tested in solution culture at pH 4.0 with 2 mol m–3N, varying the N03/NH4+ ratio up to 40% nitrate. In addition,measurements of NRA, plant chemical composition, and biomassallocation were carried out on a complete N03/NH4+ replacementseries up to 100% nitrate. With the exception of M. caerulea, the partial replacement ofNH4+ by NO3 tended to enhance the plant's growth ratewhen compared to NH4+ only. In contrast to the other species,D. flexuosa showed a very flexible response in biomass allocation:a gradual increase in the root weight ratio (RWR) with NO3increasing from 0 to 100%. In the presence of NH4+, grassesreduced nitrate in the shoot only; roots did not become involvedin the reduction of nitrate until zero ambient NH4+. The dwarfshrubs, being species that assimilate N exclusively in theirroots, displayed an enhanced root NRA in the presence of nitrate;in contrast to the steady increase with increasing NO3in Calluna roots, enzyme activity in Erica roots followed arather irregular pattern. Free nitrate accumulated in the tissuesof grasses only, and particularly in D. flexuosa. The relative uptake ratio for NO3 [(proportion of nitratein N uptake)/(proportion of nitrate in N supply)] was lowestin M. caerulea and highest in D. flexuosa. Whereas M. caeruleaand the dwarf shrubs always absorbed ammonium highly preferentially(relative uptake ratio for NO3 <0.20), D. flexuosashowed a strong preference for NO3 at low external nitrate(the relative uptake ratio for N03 reaching a value of2.0 at 10% NO3). The ecological significance of thisprominent high preference for NO3 at low NO3/NH4+ratio by D. flexuosa and its consequences for soil acidificationare briefly discussed. Key words: Ammonium, heathland lants, N03/NH4+ ratio, nitrate, nitrate reductase activity, soil acidification, specific absorption rate  相似文献   

20.
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.  相似文献   

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