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1.
Lee, H. S. J. and Griffiths, H. 1987. Induction and repressionof CAM in Sedurn relephluni L. in response to photopcnod andwater stress.J. exp. Bot. 38: 834841. The introduction and repression of CAM in Sedurn telephiunmL, a temperate succulent, was investigated in watered, progressivelydrouglited and rewatered plants in growth chambers. Measurementswere made of water vapour and CO2 exchange, titratable acidity(TA) and xylem sap tension. Effects of photoperiod were alsostudied. CAM was induced by drought under long or short days,although when watered no CAM activity was expressed. C3-CAM intermediate plants were used for the investigation ofwater supply. Those which had received water and those drought-stressedboth displayed a similar nocturnal increase in TA, with a day-nightmaximum (H+) of 69 µmol g1 fr. wt. The wateredplants took up CO2 at a maximum rate of 2?2 µmol m2s1 only in the light period, while the droughted plantsshowed a maximum nocturnal CO2 uptake rate of 0?69 µmolm2 s1. Subsequently, as CAM was repressed, thewatered S. telephiwn displayed little variation in TA, withconstant levels at 42 µmol g1 fr. wt. (day 10).After 10 d of drought stress, the CAM characteristics of S.telephiurn were aLso affected, with reduced net CO2 uptake andH+. The transition between C3 and CAM in S. telephium can be describedas a progression in terms of the proportion of respiratory CO2which is recycled and refixed at night as malic acid, in comparisonwith net CO2 uptake. Recycling increased from 20% (day 1) to44% (day 10) as a result of the drought stress and was highin both the CAM-C3 stage (no net CO2 uptake at night) and alsoin the drought-stressed CAM stage (reduced net CO2 uptake atnight). The complete C3-CAM transition occurred in less than8 d, and the stages could be characterized by xylem sap tensionmeasurements: CAM = 0?50 MPa C3-CAM = 0?36 MPa C3 = 0?29 MPa. Key words: CAM, Sedum telephium L., recycling 相似文献
2.
Hilton, J. R. and Thomas, J. A. 1987. Changes in respiratorypotential of dormant and non-dormant Galium aparine L. (cleavers)seeds during dry storage.J. exp. Bot. 38: 14841490. Pre-germinative rates of O2 uptake of two collections of Galiumaparine L. seed were compared throughout a 9 month period ofdry storage at 4 °C, 23 °C and at ambient (frost-protected)temperatures. Uptake of O2 by the dormant seeds was generallyhigher than that of the less dormant seeds except when freshly-harvested.Moreover, changes in the O2 consumption of seeds stored at ambienttemperatures could be associated with periods of germinationand seedling emergence in the field. The results are discussedin relation to changes in respiratory metabolism during dormancybreakage. 相似文献
3.
Macduff, J. H., Hopper, M. J. and Wild, A. 1987. The effectof root temperature on growth and uptake of ammonium and nitrateby Brassica napus L. CV. Bien venu in flowing solution culture.II. Uptake from solutions containing NH4NO3.J. exp. Bot.38: 5366 The effects of root temperature on uptake and assimilation ofNH4+ and NO3 by oilseed rape (Brassica napus L. CV. Bienvenu) were examined. Plants were grown for 49 d in flowing nutrientsolution at pH 6?0 with root temperature decrementally reducedfrom 20?C to 5?C; and then exposed to different root temperatures(3, 5, 7, 9, 11, 13, 17 or 25?C) held constant for 14 d. Theair temperature was 20/15?C day/night and nitrogen was suppliedautomatically to maintain 10 mmol m3 NH4NO3 in solution.Total uptake of nitrogen over 14 d increased threefold between313?C but was constant above 13?C. Net uptake of NH4+exceeded that of NO3 at all temperatures except 17?C,and represented 4765% of the total uptake of nitrogen.Unit absorption rates of NH4+ and of 1?52?7 for NO3suggested that NO3 absorption was more sensitive thanNH4+ absorption to temperature. Rates of absorption were relativelystable at 3?C and 5?C compared with those at 17?C and 25?C whichincreased sharply after 10 d. Tissue concentration of N in theshoot, expressed on a fresh weight basis, was independent ofroot temperature throughout, but doubled between 325?Cwhen expressed on a dry weight basis. The apparent proportionof net uptake of NO3 that was assimilated was inverselyrelated to root temperature. The results are used to examinethe relation between unit absorption rate adn shoot:root ratioin the context of short and long term responses to change ofroot temperature Key words: Brassica napus, oilseed rape, root temperature, nitrogen uptake 相似文献
4.
Uptake of 13C and 15N (ammonium, nitrate and urea) by Microcystis in Lake Kasumigaura 总被引:1,自引:0,他引:1
The uptake rate of carbon and nitrogen (ammonium, nitrate andurea) by the Microcystis predominating among phytoplankton wasinvestigated in the summer of 1984 in Takahamaira Bay of LakeKasumigaura. The Vmax values of Microcystis for nitrate (0.0250.046h1) and ammonium (0.150.17 h1) were considerablyhigher than other natural phytoplankton. The ammonium, nitrateand urea uptake by Microcystis was light dependent and was notinhibited with nigh light intensity. The K1 values were farlower than the Ik values. The carbon uptake was not influencedby nitrogen enrichment. Microcystis accelerated the uptake rateby changing Vmax/K s value when nitrogen versus carbon contentin cells declined. Nitrate was scarcely existent in TakahamairiBay during the summer, when Microcystis usually used ammoniumas the nitrogen source. However, the standing stock of ammoniumin the water was far lower than the daily ammonium uptake rates.Therefore, the ammonium in this water had to be supplied becauseof its rapid turn-over time (0.72.6 h). 相似文献
5.
Colman, B. and Rotatore, C. 1988. Uptake and accumulation ofinorganic carbon by a freshwater diatom.J. exp Bot 39:10251032. The mechanism of uptake of inorganic carbon and its accumulationhas been studied in the freshwater diatom Navicula pelliculosa.No external carbonic anhydrase could be detected, although itwas detected in cell extracts. The rate of photosynthetic O2evolution, in media in the range pH 7.58.5, exceededthe calculated rate of CO2 supply 2- to 5-fold, indicating thatHCO3 was taken up by the cells. At an external pH of7.5, the internal pH, measured by 14C-dimethyloxazolidine-2,4-dione distribution between the cells and the medium, was pH7.6 in the light and pH 7.4 in the dark. Accumulation of inorganiccarbon was determined by the silicone oil centrifugation methodand inorganic carbon pools of 23.5 mol m3 were found,a concentration 21.6-fold that in the external medium. The resultsindicate an active accumulation of inorganic carbon againstpH and concentration gradients in this diatom, probably by activeHCO3 uptake. Key words: Bicarbonate transport, carbon dioxide, carbonic anhydrase, CO2 affinity, CO2 concentrating mechanism, internal pH, Navicula pelliculosa 相似文献
6.
The Permeability of Ammonia, Methylamine and Ethylamine in the Charophyte Chara corallina (C. australis) 总被引:1,自引:0,他引:1
Ritchie, R. J. 1987. The permeability of ammonia, methylamineand ethylamine in the charophyte Chara corallina (C. australis).J.exp. Bot. 38: 6776 The permeabilities of the amines, ammonia (NH3), methylamine(CH3NH2) and ethylamine (CH3CH2NH2) in the giant-celled charophyteChara corallina (C. australis) R.Br. have been measured andcompared. The permeabilities were corrected for uptake fluxesof the amine cations. Based on net uptake rates, the permeabilityof ammonia was 6?4?0?93 µm s1 (n = 38). The permeabilitiesof methylamine and ethylamine were measured in net and exchangeflux experiments. The permeabilities of methylamine were notsignificantly different in net and exchange experiments, norto that of ammonia (Pmethylamine = 6?0?0?49 µm s1(n = 44)). In net flux experiments the apparent permeabilityof ethylamine was slightly greater than that of ammonia andmethylamine (Pethylamine, net = 8?4?1?2 µm s1 (n= 40)) but the permeability of ethylamine based on exchangeflux data was significantly higher (Pethylamine, exchange =14?1?2 µm s1 (n = 20)). Methylamine can be validlyused as an ammonium analogue in permeability studies in Chara. The plasmalemma of Chara has acid and alkaline bands; littlediffusion of uncharged amines would occur across the acid bands.The actual permeability of amines across the alkaline bandsis probably about twice the values quoted above on a whole cellbasis i.e. the permeability of ammonia across the permeablepart of the plasmalemma is probably about 12 µm s1. Key words: Chara, permeability, ammonia, methylamine 相似文献
7.
The marine green alga, Chlorococcum littorale, accumulated ironin its cells and showed high activity of plasma membrane ferricreductase under high-CO2 and iron-deficient conditions. Theseactivities disappeared upon exposure to ordinary air and byadding excess FeSO4. The iron uptake had high affinity for theFe(II) form (Km of 0.13 µM). Carbonylcyanide m-chlorophenylhydrazoneand N,N-dicyclohexylcarbodiimide significantly suppressed theiron uptake, suggesting that the Fe(II) uptake was driven byATPase. These results indicate that high CO2 and iron deficiencycooperatively induce the Fe(II) uptake and cell-surface ferricreductase activity. (Received October 20, 1997; Accepted January 29, 1998) 相似文献
8.
The photosynthetic uptake of root-zone CO2 was determined forEriocaulon septangulare, Gratiola aurea, Isoetes macrospora,Littorella uniflora var. americana and Lobelia dortmanna aspart of a study of the photosynthetic carbon economy of submergedaquatic isoetids. The pH and dissolved inorganic carbon (DIC)of the sediment interstitial water in four Wisconsin lakes reflectedthe water column character, where the DIC increased with depthin the sediment to concentrations five to ten times those ofthe water column. Sediment free CO2 concentrations were 550times those in the water column and were similar at all sites(about 051.0mM CO2 in the root-zone). In pH-driftstudies these plants were unable to take up HCO2. Laboratory determinations of the carbon uptake from the rootand shoot-zones were made for all five species. These experimentsshowed that CO2 in the root-zone accounted for 6595 percent of external carbon uptake for the five species. For G.aurea and E. septangulare, root-zone CO2 was > 85 per centof carbon uptake. Carbon, CO2, photosynthesis, sediment, isoetid, Eriocaulon septangulare, Gratiola aurea, Isoetes macrospora, Littorella uniflora, Lobelia dortmanna 相似文献
9.
Hansen, A. P. and Pate, J. S. 1987. Comparative growth and symbioticperformance of seedlings of Acacia spp. in defined pot cultureor as natural understorey components of a eucalypt forest ecosystemin S.W. Australia.J. exp. Bot. 38: 1325 Growth, nitrogen accumulation, nodulation and nitrogenase activity(C2H2 reduction activity) were monitored in a dense stand ofseedlings of Acacia pulchella R.Br. and A. alata R.Br. duringtwo growing seasons after fire at a jarrah (Eucalyptus marginataDonn ex Sm.) forest site at Illawarra, 35 km south-east of Perth.Nitrogen fixation, estimated by a previously calibrated C2H2reduction assay, was essentially restricted to the winter andspring months (July to October) and was estimated to contribute37% and 9% respectively of the total N accumulated by A. pulchelladuring the first and second seasons of growth. Comparable valuesfor A. alata were 29% and 2%. Comparisons with fully symbioticplants raised in a glasshouse in supposedly non-limiting growthconditions in minus nitrogen sand culture indicated that waterstress rather than high temperatures was responsible for lossof nodules, cessation of symbiotic activity and attenuationof growth during summer in the field. By 19 months glasshouseplants had gained 130230 times the dry weight and accumulated110160 times the total N of similarly aged, field grownplants. Growth, nodulation and N2 fixation of symbiotically-dependentsand cultured plants of A. pulchella and A. alata respondedmarkedly to phosphate, and additions of water and nutrientsto 3-year plants of A. pulchella during a winter growing seasonin the field indicated that periods of reduced soil moistureand low availability of nutrients, particularly phosphorus,might limit symbiotic performance under natural conditions. Key words: Seasonal nitrogen fixation, Acacia spp 相似文献
10.
By growing Chlorella ellipsoidea synchronously by the techniqueof TAMIYA et al. with some modifications, it was demonstratedthat cellular division of ripened cells (L2- and L3-cells) inthe dark is specifically inhibitedespecially stronglyat pH 6.3by cupric ion present in the medium. The possibleattack site of cupric ion in cellular division of this algais discussed. (Received March 12, 1969; ) 相似文献
11.
Careri, G., Giansanti, A. and Fensom, D. 1986. Dielectnc-gravimetricmeasurements on Fucus vesiculosus and Ascophyllum nodosum duringdehydration.J. exp. Bot. 37: 375378. Samples of the marine algae Fucus vesiculosus and Ascophyllumnodosum were dehydrated between plates of a condenser so thatsimultaneous measurements of dielectric properties and rateof water loss could be made. During the desiccation process,both the evaporation rate and the dielectric properties becomezero at a critical hydration Hc, indicating that for H <Hc,the residual water must be in a tightly bound state. The absolutevalues of Hc, depend on the nature of the sample, but they arein the range 0·10·3, well above the hydrationlimit for active ion uptake (H=0·02). It is concludedthat, in these fucoids, living cells are maintained in the hydrationregion where water is in the bound state only. Key words: Fucus, Ascophyllwn, dielectric, dehydration 相似文献
12.
BORER K.; HARDY R. J.; LINDSAY W. S.; SPRATT D. A.; MEES G. C. 《Journal of experimental botany》1966,17(2):378-389
The results of a systematic attempt to relate the growth-stimulatingfunction of compounds analogous to ethylene-bis-nitrourethaneto their chemical structure and properties showed that, withthe exception of a series of nitraminocarboxylic acids, NO2NH(CH2)COOH,activity was confined to compounds of the form RN(NO2)XN(NO2)R,where X is an alkylene or substituted alkylene chain. It issuggested that active compounds are converted to dinitramines(R = H) in the plant, and that the acidic nature of the NHNO2groups is of importance. The oil/water partition coefficientsand the geometrical structure of the molecules are also shownto influence their growth-stimulating activity. 相似文献
13.
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 m3N, 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
14.
Inhibition of photosynthesis by Na2SO3 in mesophyll protoplastsisolated from Vicia faba leaves and uptake of sulfite by theprotoplasts were examined at various pH values of the incubationmedium containing Na2SO3. As the pH of the incubation mediumlowered, the rate of photosynthesis in the protoplasts decreasedand the amount of sulfite taken up by the protoplasts increased.Most of sulfite accumulated in the protoplasts was not metabolizedduring the dark incubation, as measured with an ion chromatograph.Photosynthetic O2 evolution by the chloroplasts isolated fromVicia mesophyll protoplasts was inhibited by exogenously-appliedNa2SO3 over pH region examined (7.49.0). The sulfiteconcentration required for a half inhibition of photosynthesisby the isolated chloroplasts was similar to the intracellularsulfite level required for that by the protoplasts. These resultsindicate that the intracellular sulfite accumulated in the protoplastsin an unmetabolized state is responsible for the inhibitionof protoplast photosynthesis. (Received January 24, 1985; Accepted May 29, 1985) 相似文献
15.
Kreuzwieser Jrgen; Herschbach Cornelia; Stulen Ineke; Wiersema Peter; Vaalburg Willem; Rennenberg Heinz 《Journal of experimental botany》1997,48(7):1431-1438
The processes of NO3 uptake and transport and the effectsof NH4+ or L-glutamate on these processes were investigatedwith excised non-mycorrhizal beech (Fagus sylvatica L.) roots.NO3 net uptake followed uniphasic Michaelis-Menten kineticsin a concentration range of 10µM to 1 mM with an apparentKm of 9.2 µM and a Vmax of 366 nmol g1 FW h1.NH4+, when present in excess to NO3, or 10 mM L-glutamateinhibited the net uptake of NO3 Apparently, part of NO3taken up was loaded into the xylem. Relative xylem loading ofNO3 ranged from 3.21.6 to 6.45.1% of NO3 netuptake. It was not affected by treatment with NH4+ or L-glutamate.16N/13N double labelling experiments showed that NO3efflux from roots increased with increasing influx of NO3and, therefore, declined if influx was reduced by NH4+ or L-glutamateexposure. From these results it is concluded that NO3net uptake by non-mycorrhizal beech roots is reduced by NH4+or L-glutamate at the level of influx and not at the level ofefflux. Key words: Nitrate transport, net uptake, influx, efflux, ammonium, Fagus, Fagaceae 相似文献
16.
MATTSSON M; JOHANSSON E; LUNDBORG T.; LARSSON M.; LARSSON C.-M. 《Journal of experimental botany》1991,42(2):197-205
Growth and nitrate uptake kinetics in vegetatively growing barley(Hordeum vulgare L., cvs Laevigatum, Golf, and Mette) were investigatedin solution culture under long-term limitations of externalnitrogen availability. Nitrate was fed to the cultures at relativeaddition rates (RA) ranging from 0.02 to 0.2 d1. Therelative growth rate (RG, calculated for total plant dry weight)correlated well with RA in the range 0.02 to 0.07 d1.In the RA range from 0.07 to 0.2 d1 RG continued to increase,but an increasing fraction of nitrogen, added and absorbed,was apparently stored rather than used for structural growth.The RG of the roots was less affected by RA. Vmax, for net nitrateuptake increased with RA up to 0.11 d1, but decreasedat higher RA. The decline in Vmax coincided with a build-upof nitrate stores in both roots and shoots. Vmax, expressedper unit nitrogen in the plants (the relative Vmax, was higherthan required for maintenance of growth (up to 30-fold) at lowRA, whereas at higher RA the relative Vmax decreased. Kineticpredictions of steady-state external nitrate concentrationsduring N-limited growth ranged from 0.2 to 5.0 mmol m3over the RG range 0.02 to 0.11 d1. It is suggested thatthe nitrate uptake system is not under specific regulation atlow RA, but co-ordinated with root protein synthesis and growthin general. At RA higher than 0.11 d1, however, specificregulation of nitrate uptake, possibly via root nitrate pools,become important. The three cultivars showed very similar growthand nitrate uptake characteristics. Key words: Barley, growth, nitrogen limitation, nitrate uptake, kinetics 相似文献
17.
The Regulation of Citric Acid Accumulation and Carbon Recycling During CAM in Ananas comosus 总被引:4,自引:0,他引:4
The carbon balance of shade-grown Ananas comosus was investigatedwith regard to nitrogen supply and responses to high PAR. Netdark CO2 uptake was reduced from 61.2 to 38.5 mmol CO2 m2in N limited (N) plants grown under low PAR (60 µmolm2 s1) and apparent photon yield declined from0.066 to 0.034 (mol 02.mol1 photon), although photosyntheticcapacities (measured under 5% CO2) were similar. Following transferfor 7 d to high PAR (600. µmol m2 s1), netCO2 uptake at night increased by 14% in +N plants, and daytimephotosynthetic capacity was higher, with a maximum value of7.8 µmol m2 s1. The magnitude of dark CO2 fixation during CAM was measured asdawndusk variations in leaf-sap titratable acidity (H+)and as the proportion of malic and citric acids. The contributionfrom re-fixation of respiratory CO2 recycling (measured as thedifference between net CO2 uptake and malic acid accumulation)varied with growth conditions, although it was generally lower(30%) than reported for other bromeliads. Assuming a stoichiometryof 2H+: malate and 3H+: citrate, there was a good agreementbetween titratable protons and enzymatically determined organicacids. The accumulation of citric acid was related to nitrogensupply and PAR regime, increasing from 7.0 mol m3 (+Nplants) to 18 mol m3 (N plants) when plants weretransferred to high PAR; malate: citrate ratios decreased from13.1 to 2.5 under these conditions. Under the low PAR regime, leaf-sap osmotic pressure increasedat night in proportion to malic acid accumulation. However,following the transfer to high PAR for 7 d, there was a muchgreater depletion of soluble sugars at night which correspondedto a decrease in leaf-sap osmotic pressure. Although a rolefor citric acid in CAM has not been properly defined, it appearsthat the accepted stoichiometry for CAM in terms of gas exchange,titratable acidity, malic acid and osmotic pressure may nothold for plants which accumulate citric acid. Key words: Ananas comosus, CAM, citric acid accumulation, carbon recycling 相似文献
18.
Nitrate provision has been found to regulate the capacity forChara corallina cells to take up nitrate. When nitrate was suppliedto N sufficient cells maximum nitrate uptake was reached after8 h. Prolonged treatment of the cells in the absence of N alsoresulted in the apparent ability of these cells to take up nitrate.Chlorate was found to substitute partially for nitrate in theinduction step. The effects on nitrate reductionwere separated from those on nitrate uptake by experiments usingtungstate. Tungstate pretreatment had no effect on NO3uptake induced by N starvation, but inhibitedNO3 uptake associated with NO3 pretreatment. Chloridepretreatment similarly had no effect on NO3 uptake inducedby N deprivation, but inhibited NO3 uptake followingNO3 pretreatment. The data suggest that there are atleast two mechanisms responsible for the inductionof nitrate uptake by Chara cells, one associated with NO3reduction and induced by CIO3 or NO3and one associated with N deprivation. Key words: Nitrate, Chlorate, Chara corallina, Induction 相似文献
19.
Sagebrush (Artemisia tridentata Nutt.) roots maintain nutrient uptake capacity under water stress 总被引:2,自引:0,他引:2
Phosphorus and nitrogen uptake capacities were assessed during3658 d drying cycles to determine whether the abilityof sagebrush (Artemisia tridentata Nutt.) to absorb these nutrientschanged as the roots were subjected to increasing levels ofwater stress. Water was withheld from mature plants in large(6 I) containers and the uptake capacity of excised roots insolution was determined as soil water potentials decreased from0.03 MPa to 5.0 MPa. Phosphorus uptake rates of excised roots at given substrateconcentrations increased as preharvest soil water potentialsdecreased to 5.0 MPa. Vmax and Km also increased as soilwater potentials declined. Declining soil water potentials depressednitrogen uptake at set substrate concentrations, but uptakecapacity, calculated as the sum Vmax for both NH+4+NO3,did not change significantly with drying. The sum Vmax correlatedwith root nitrogen concentration. Root uptake capacity for nitrogen and phosphorus was extremelystable under severe water stress in this aridland shrub. Maintenanceof uptake capacity, coupled with a previously demonstrated abilityto conduct hydraulic lift, may enable A. tridentata better tomaintain nitrogen and phosphorus uptake as soil water availabilitydeclines. These mechanisms may be important in the ability ofA. tridentata to maintain growth, complete reproduction, andgain an advantage against competitors late in the season whenthe soil layers with higher nutrient availability are dry. Key words: Kinetics, nitrogen, phosphorus, roots, water stress 相似文献
20.
Dwarf french beans (Phaseolus vulgaris var. Canadian Wonder)were grown in chambers at 25?C with the roots aerated at 20per cent oxygen and tops variously maintained at: T1 O2 0.21;CO2 270?106: T2; O2 0.05, CO2, CO2 270?106: T3;O2 0.21; CO2 550?106. Experiment 1 (T1 and T2) lasted2 weeks: Experiment 2 (T1 T2 and T3) only one week. Hourly estimatesof CO2 uptake were made by gas analysis and weekly estimatesof fresh weight, dry matter in tops and roots, and leaf area,by sampling. Light intensity was 80 W m2 of photosyntheticallyactive radiation. An attempt was made to explain the results in terms of a simplelight absorption model such that
where dV/dt is the rate of CO2 uptake per plant, ßis the photosynthetic efficiency, I0 is the incident light intensity,f is the fraction of incident light absorbed by unit leaf layerand L is the leaf area index. The analysis showed that ß(T2)was at least double ß(T1), whilst f(T2) was smallerthan f(T1) at a given leaf area. The results also required thatthroughout the period of the experiment, fL(T1)=fL(T2) at anygiven time, i.e. the treatment with the larger leaf area (T2)has the smaller value of f, and therefore intercepts less lightper unit leaf area. This could be advantageous for plant growth,but requires further experiments. The photosynthetic rates per unit leaf are about 40 per centgreater in T2 than T1. Over the relatively short period of the experiment the resultsare adequately described by U=btn, where U is the accumulatedcarbon dioxide uptake, b is related to the photosynthetic efficiency(different for the differing treatments), and n is a constant(similar for all treatments). This relationship with time isbelieved to be a relationship with accumulated radiation, forthe light was constant throughout the experiments. Comparisons of carbon fixed (measured gas uptake) and dry matteraccumulation (sampling) show great scatter with an average valueof 0.43. The first week's results were generally smaller thanthis value and the second week's greater. Energy fixation as a fraction of photosynthetically active radiationon the ground area covered by the plants ranged from 3.5 to10 per cent. The results from treatment T3 were similar to T2 suggestingthat increasing CO2 concentration decreases the growth inhibitionat 21 per cent O2. 相似文献