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1.
The Effects of Low Concentrations of Sulphur Dioxide on Stomatal Conductance and Epidermal Cell Survival in Field Bean (Vicia faba L.) 总被引:4,自引:0,他引:4
Exposure of 3 week old field bean plants to concentrations ofSO2 from 50500 µg m-3 induced comparable 2025%increases in mean leaf diffusive conductance regardless of whetherthe diffusive conductances were obtained by porometric measurementor calculation from gas exchange data. The stomatal conductancesof the adaxial and abaxial leaf surfaces were both increasedby exposure to SO2. Microscopic examination of epidermal strips from control andpolluted plants revealed that the stomatal opening observedin treated plants was associated with a sharp reduction in theproportion of living epidermal cells adjacent to the stomata.The proportion of surviving adjacent epidermal cells was invariablysmaller on the lower epidermis and appeared to decrease as theSO2 concentration was raised from 50 to 500 µg m3.Although the guard cells appeared to be undamaged at concentrationsbelow 200 µg m3, structural disorganization ordeath of one or both guard cells was observed frequently ator above 500 µg m3. The results are discussed in relation to the controversy concerningthe effects of SO2 on stomatal aperture. 相似文献
2.
Exposure of ryegrass (Lolium perenne L.) cv. S23 to 0, 50, and400 µg m3 SO2 for an initial 29 d (first harvest),and for an additional 22 d period of regrowth (second harvest),resulted in distinct alterations in carbohydrate metabolismat each harvest. At the first harvest, exposure to 50 µgm3 increased concentrations of free and total carbohydrates,whereas exposure to 400 µg m3 resulted in concentrationshardly different from those in control plants. At both SO2 concentrations,more assimilate was retained as free carbohydrate rather thanas storage carbohydrate. Comparison of assimilate distributionat the end of the light, and at the end of the dark period atthe first harvest led to the conclusion that light-mediatedmetabolism is more sensitive to SO2 exposure than dark metabolism,and that assimilate distribution might be controlled by at leasttwo processes exhibiting different SO2 sensitivities. 相似文献
3.
Apparatus is described for exposing plants to low concentrationsof SO2 (50500µg m3 in air) and for measuringeffects on photosynthesis, dark respiration, and transpiration.Temperature, humidity, and irradiance in the chambers were controlledindependently, and fans ensured that leaf boundary layer resistanceswere low. Experiments with plants of Vicia faba in clean andpolluted air showed that: (i) a depression of net photosynthesisby 50 µg m3 SO2 depended on boundary layer resistanceand on irradiance; (ii) stomatal resistance was increased ordecreased by 50 µg m3 SO2 when relative humidityin the chambers was low (35% r.h., 22 °C) or high (50% r.h.,22 °C) respectively. 相似文献
4.
5.
Growth of Perennial Ryegrass (Lolium perenne L.) Exposed to a Low Concentration of Sulphur Dioxide 总被引:3,自引:0,他引:3
The influence of a low concentration of SO2 on the growth andsulphur status of perennial ryegrass (Lolium perenne L.) cv.S23 was examined in a system of specially designed growth chambers.For plants grown without additions of sulphate to the soil,erposure to ifitered air containing 50 µg m3 SO2alleviated sulphur deficiency that developed during a sequenceof successive harvests, and gave increased yield. The plantshad higher contents of organic and inorganic sulphur than thosegrown with neither sulphate nor SO2. Plants grown with addedsulphate showed no signs of sulphur deficiency and althoughexposure to SO2 increased their sulphur content it had no effecton yield. The coefficient of transpiration (g water transpiredg1 dry wt. of shoots) was reduced when plants which otherwisehad an inadequate supply of sulphur were exposed to SO2; forplants with adequate supplies of sulphate, it was similar whetherthey were grown with or without the addition of SO2 to the air.The results are discussed in relation to other known reactionsof plants to SO2. 相似文献
6.
Perennial ryegrass (Lolium perenne L.) cv. S23 was exposed to0, 50, and400 µg m 3 SO2 for a 29 d period, harvested,and then exposed under the same regime for a further 22 d periodof regrowth. Leaves from plants representing each exposure concentrationwere photosynthetically fed 14CO2 for 5 min at the end of eachperiod. A significant increase in photoassimilation of 14CO2and retention of I4C, concomitant with significant decreasesin [14C]glycine and [14C]serine with increasing SO2 concentration,implied that there was an inhibition of the photorespiratorypathway. At the second harvest, leaves from plants exposed to400 µg m 3 SO2 also exhibited significant increasesin [14C]sucrose and [14C]fructose. 相似文献
7.
Absorption of SO2 by Pecan (Carya illinoensis (Wang) K. Koch) and Alfalfa (Medicago sativa L.) and its Effect on Net Photosynthesis 总被引:1,自引:0,他引:1
SISSON WILLIAM B.; BOOTH J. A.; THRONEBERRY GLYN O. 《Journal of experimental botany》1981,32(3):523-534
Absorption rates of SO2 by pecan (Carya illinoensis (Wang) K.Koch) leaflets exposed to 2.6, 5.2, and 7.8 mg SO2 m3were measured over a 2 h period. SO2 was rapidly absorbed bythe leaflets in all treatments during the initial 3050min; the rate of uptake decreased to a rather constant levelthereafter. Total SO2 absorbed during the 2 h period was 15.6,25.6, and 38.9 nmol cm2 for the low, medium, and highSO2 concentrations, respectively. Reductions in net photosyntheticrates were proportional to ambient SO2 concentrations and totalSO2 absorbed. Partial photosynthetic recovery occurred in alltreatments during a 2 h post-treatment period and full recoveryoccurred during a 12 h dark period. Exposure to SO2 resultedin slight increases in stomatal and boundary layer resistancesto CO2 and substantial increases in residual resistances. Absorptionrates of SO2 by alfalfa (Medicago saliva L.) exposed to 5.2mg SO2m3 for 1 h were approximately double those of pecanexposed to the same ambient SO2 concentration. Alfalfa net photosyntheticrates were reduced 74% after 1 h exposure to 5.2 mg SO2 m3while a depression of 42% occurred in pecan. 相似文献
8.
The effect of exposure to sulphur dioxide (0 or 96 µgm3 SO2) on the growth and sulphur content of lucerne(Medicago sativa L.) was examined in a period of 135 d duringwhich the plants were harvested four times. The lucerne wasgrown in pots of soil with and without the addition of sulphateand of nitrate. Evidence of sulphur deficiency, including areduction in the weight, the number and the sulphur contentof shoots, was found in plants grown without added sulphate.Deficiency was alleviated through exposure of plants to SO2.Apart from reducing shoot weight at one harvest and generallyincreasimg the concentration of sulphur in the shoots, exposureto SO2 had no significant effect on plants grown with addedsulphate. The yield of shoots was greater, and was reduced toa lesser extent with sulphur deficiency, in plants grown withadded nitrate than in those dependent on rhizobia. Whilst thetranspiration coefficient increased greatly in sulphur-deficientplants, it was reduced where otherwise similarly treated plantswere exposed to SO2; this treatment did not alter the coefficientin plants with an adequate supply of sulphur from the soil. 相似文献
9.
Imsande, J. 1986. Inhibition of nodule development in soybeanby nitrate or reduced nitrogen.J. exp. Bot. 37: 348355. Nodulation of hydroponically grown soybean plants [Glycine max(L.) Merr.] is inhibited by continuous growth in the presenceof 4· mol m3 KNO3 The presence of 4·0 molm3 starter nitrate for 3-6 d during noduledevelopment, however, subsequently stimulates nodule dry weightaccumulation and nitrogenase activity. These stimulations occureven though 4· mol m3 nitrate temporarily delaysnodule development, i.e. the late steps of nodule developmentare reversibly inhibited by a short-term exposure to 4·0mol m3 nitrate. On the other hand, treatment with 4·0mol m3 nitrate in excess of 14 d significantly reducesnodule dry weight Thus, extended growth in the presence of 4·0mol m3 KNO3 seems to block both early and late stepsof nodule development. Nodulation of hydroponically grown soybeansis also inhibited by continuous growth in the presence of 2·0mol m3 (NH4)2SO4 This inhibition is not caused by acidityof the growth medium. On the other hand, nodule development6 d after inoculation with Rhizoblum japonicum is not delayedby a 7-d exposure to 2·0 mol m3 (NH4)2SO4 butis partially inhibited by a prolonged exposure to (NH4)2SO4Because repression of nodulation by 4·0 mol m3KNO3 is more severe than that by 2·0 mol m3 (NH4)2SO4and because ammonium taken up by the soybean plant is not activelyoxidized to nitrate, it is suggested that there are at leasttwo mechanisms by which nitrate utilization represses noduleformation in soybean. Key words: Glycine max, nitrogen, nitrogen fixation, nodulation 相似文献
10.
The effects of exposure to SO2 (50 and 400 µg m3SO2) on the growth, photosynthesis, and respiration of perennialryegrass (Lolium perenne L.) cv. S23 were examined in two successivegrowth periods of 29 and 22 d. At the higher concentration ofSO2, there was some visible injury of the leaves and specificleaf area was reduced, but yield, net photosynthesis, and darkrespiration of the plants were not significantly affected byexposure. The treatment was also without effect on the transpirationcoefficient of the plants and their number of tillers. The plantsexposed to the lower concentration of SO2 showed no signs ofinjury and did not differ in any of the measured characteristicsfrom plants grown in SO2-free air. Content of S in the shootsincreased linearly with the concentration of SO2, the additionalS being found in the sulphate fraction whilst organic S wasunchanged. The results are discussed in relation to earlierfindings that yield of ryegrass exposed to SO2 may be reducedwithout visible signs of injury. 相似文献
11.
Whitehead, D. C. and Lockyer, D. R. 1986. The influence of theconcentration of gaseous ammonia on its uptake by the leavesof Italian ryegrass, with and without an adequate supply ofnitrogen to the roots.J. exp. Bot. 38: 818827. Plants of Italian ryegrass (Lolium multiflorum Lam.) were grownin pots of soil with two rates of 15N-labclled nitrate, oneproviding adequate, and the other less than adequate, N formaximum growth. After 25 d in a controlled environment cabinet,the plants were transferred to chambers and exposed for 33 dto NH3in the air at one of nine concentrations ranging from14 to 709 µg NH3 m3. Increasing the concentrationof NH3 in the air increased the dry weight of the shoots ofplants grown at the lower but not the higher rate of nitrate.The content of total N in the plant shoots (% dry weight) waslinearly related to NH3 concentration; at 709 µg NH3 andin both sets of plants it was more than double the content at14 µg NH3 m3. Calculations, based on 15N enrichment,indicated that the amount of N taken up from the NH3 per unitleaf area increased linearly with increasing concentration ofNH3 in the air uptake (µg dm2 h1) = 0.1009xat the lower rate of nitrate and 0-0829x at the higher rateof nitrate, where x is the concentration of NH3 in the air expressedas µg NH3m3. The proportion of the total plant N that was derived from theNH3 ranged from 4?0% at a concentration of 14 µg NH3 m3with the higher rate of nitrate addition to 77?5% at a concentrationof 709 µg m3 with the lower rate of nitrate addition.The proportions of the total N in the water-insoluble proteinof the leaf tissue that were derived from nitrate and gaseousNH3 were similar to the proportions in the whole leaf material. Key words: Ammonia, nitrogen, leaf sorption, Lolium multiflorum 相似文献
12.
Responses of CO2 assimilation to changes in irradiance: laboratory and field data and a model for beans (Phaseolus vulgaris L.) 总被引:1,自引:0,他引:1
The responses of net CO2 assimilation to sudden changes in irradiancewere studied in Phaseolus vulgaris L. in the laboratory andthe field. For irradiance changes between 50 µmol m2s1 to 350 µmol m2 s1 in the laboratory,assimilation rate increased with half-times of 2.7 and 4.1 minin well-watered and water-stressed plants, respectively. Ina field experiment with a change in irradiance from 400 to 1200µmol m2 s1 the response was faster (half-time=c.1.2 min). In all cases when irradiance was returned to a lowvalue, assimilation declined rapidly with a half-time of approximately1 min, which approached the time resolution of the gas-exchangesystem. The corresponding changes in stomatal conductance in responseto both increasing and decreasing irradiance were much slowerthan the assimilation responses, indicating that biochemicalprocesses, rather than CO2 supply, primarily determined theactual rate of assimilation in these experiments. The conceptof stomatal limitation to photosynthesis is discussed in relationto these results. A simple model for assimilation in a fluctuating light environmentis proposed that depends on a steadystate light response curve,an induction lag on increasing irradiance, andan induction-state memory. The likely importance of taking accountof such induction lags in natural canopy microclimates is considered. Key words: Models, Phaseolus vulgaris, photosynthetic induction, CO2 assimilation, stomatal limitation, sunflecks, water stress 相似文献
13.
The mechanism of SO2-induced changes in stomatal conductance(g) of alder was examined to determine if SO2 affects guardcell function directly or indirectly through the SO2-inducedchanges in photosynthesis. During experimental fumigations at SO2 concentrations of 33µmol m3 (0.08 µl l1), stomatal closurepreceded declines in net photosynthetic rate (A), indicatingthat SO2 can directly affect guard cells. From these and otherstudies it appears that the sequence of A and g responses maybe influenced by SO2 concentration as well as by species. Fumigation with SO2 did not cause increases in g, even whenthe intercellular substomatal CO2 concentration (ci) was reducedby 50 µmol mol1. Increases in g are not attributableto SO2 effects on the CO2-based stomatal control system. Key words: Air pollution, Alnus serrulata, gas exchange, stomata, sulphur dioxide 相似文献
14.
Hogan K.P.; Fleck I.; Bungard R.; Cheeseman J.M.; Whitehead D. 《Journal of experimental botany》1997,48(6):1289-1297
Red beech (Nothofagus fusca (Hook. F.) Oerst.; Fagaceae) andradiata pine (Pinus radiata D. Don; Pinaceae) were grown for16 months in large open-top chambers at ambient (37 Pa) andelevated (66 Pa) atmospheric partial pressure of CO2, and incontrol plots (no chamber). Summer-time measurements showedthat photosynthetic capacity was similar at elevated CO2 (lightand CO2-saturated value of 17.2 µmol m2 s1for beech, 13.5 µmol m2 s1 for pine), plantsgrown at ambient CO2 (beech 21.0 µmol2 s1,pine 14.9 µmol m2s1) or control plants grownwithout chambers (beech 23.2 µmol m2 s1,pine 12.9 µmol m2 s1). However, the higherCO2 partial pressure had a direct effect on photosynthetic rate,such that under their respective growth conditions, photosynthesisfor the elevated CO2 treatment (measured at 70 Pa CO2 partialpressure: beech 14.1 µmol m2 s1 pine 10.3)was greater than in ambient (measured at 35 Pa CO2: beech 9.7µmol m2 s1, pine 7.0 µmol m2s1) or control plants (beech 10.8 µmol m2s1, pine 7.2 µmol m2 s1). Measurementsof chlorophyll fluorescence revealed no evidence of photodamagein any treatment for either species. The quantity of the photoprotectivexanthophyll cycle pigments and their degree of de-epoxidationat midday did not differ among treatments for either species.The photochemical efficiency of photosystem II (yield) was lowerin control plants than in chamber-grown plants, and was higherin chamber plants at ambient than at elevated CO2. These resultssuggest that at lower (ambient) CO2 partial pressure, beechplants may have dissipated excess energy by a mechanism thatdoes not involve the xanthophyll cycle pigments. Key words: Carotenoids, chlorophyll fluorescence, photosynthesis, photoinhibition, photoprotection, xanthophyll cycle 相似文献
15.
Single clonal plants of white clover (Trifolium repens L) grownfrom explants in a Perlite rooting medium, and dependent fornitrogen on N2 fixation in root nodules, were grown for severalweeks in controlled environments which provided two regimesof CO2, and temperature 23/18 °C day/night temperaturesat 680 µmol mol1 CO2, (C680), and 20/15 °Cday/night temperatures at 340 µmol mol1 CO2 (C340)After 34 weeks of growth, when the plants were acclimatedto the environmental regimes, leaf and whole-plant photosynthesisand respiration were measured using conventional infra-red gasanalysis techniques Elevated CO2 and temperature increased ratesof photosynthesis of young, fully expanded leaves at the growthirradiance by 1729%, despite decreased stomatal conductancesand transpiration rates Water use efficiency (mol CO2 mol H2O1)was also significantly increased Plants acclimated to elevatedCO2, and temperature exhibited rates of leaf photosynthesisvery similar to those of C340 leaves instantaneouslyexposed to the C680 regime However, leaves developed in theC680 regime photosynthesised less rapidly than C340 leaves whenboth were exposed to a normal CO2, and temperature environmentIn measurements where irradiance was varied, the enhancementof photosynthesis in elevated CO2 at 23 °C increased graduallyfrom approx 10 % at 100 µmol m1 s1 to >27 % at 1170 µmol m2 s1 In parallel, wateruse efficiency increased by 2040 % at 315 µmolm2 s1 In parallel, water use efficiency increasedby 2040 % at 315 µmol m2 s1 In parallel,water use efficiency increased by 2040 % at 315 µmolm2 s1 In parallel, water use efficiency increasedby 2040 % at 315 µmol m2 s1 to approx100 % at the highest irradiance Elevated CO2, and temperatureincreased whole-plant photosynthesis by > 40 %, when expressedin terms of shoot surface area or shoot weight No effects ofelevated CO2 and temperature on rate of tissue respiration,either during growth or measurement, were established for singleleaves or for whole plants Dependence on N2, fixation in rootnodules appeared to have no detrimental effect on photosyntheticperformance in elevated CO2, and temperature Trifolium repens, white clover, photosynthesis, respiration, elevated CO2, elevated temperature, water use efficiency, N2 fixation 相似文献
16.
The relationships between CO2 concentrating mechanisms, photosyntheticefficiency and inorganic carbon supply have been investigatedfor the aquatic macrophyte Littorella uniflora. Plants wereobtained from Esthwaite Water or a local reservoir, with thelatter plants transplanted into a range of sediment types toalter CO2 supply around the roots. Free CO2 in sediment-interstitial-waterranged from 101 mol m3 (Esthwaite), 0.79 mol m3(peat), 0.32 mol m3 (silt) and 017 mol m3(sand), with plants maintained under PAR of 40 µmol m2s1. A comparison of gross morphology of plants maintained underthese conditions showed that the peat-grown plants with highsediment CO2 had larger leaf fresh weight (069 g) andtotal surface area (223 cm2 g1 fr. wt. including lacunalsurface area) than the sand-grown plants (0.21 g and 196 cm2g1 fr. wt. respectively). Root fresh weights were similarfor all treatments. In contrast, leaf internal CO2 concentration[CO2], was highest in the sand-grown plants (269 molm3, corresponding to 6.5% CO2 in air) and lowest inthe Esthwaite plants (108 mol m3). Expressionof CAM in transplants was also greatest in the low CO2 regime,with H+ (measured as dawn-dusk titratable acidity) of 50µmolg fr. wt., similar to Esthwaite plants in natural sediment.Assuming typical CAM stoichiometry, decarboxylation of malatecould account largely for the measured [CO2]1 and would makea major contribution to daytime CO2 fixation in vivo. A range of leaf sections (02, 10, 50 and170 mm) was used to evaluate diffusion limitation andto select a suitable size for comparative studies of photosyntheticO2 evolution. The longer leaf sections (17.0 mm), which weresealed and included the leaf tip, were diffusion-limited witha linear response to incremental addition of CO2 and 10mol m3 exogenous CO2 was required to saturate photosynthesis.Shorter leaf sections were less diffusion-limited, with thegreatest photosynthetic capacity (36 µmol O2 g1 fr. wt. h1) obtainedfrom the 1.0 mm size and were not infiltrated by the incubatingmedium. Comparative studies with 1.0 mm sections from plants grown inthe different sediment types revealed that the photosyntheticcapacity of the sand-grown plants was greatest (45 µmolO2 g1 fr. wt. h1) with a K0.5 of 80 mmol m3.In terms of light response, saturation of photosynthesis intissue slices occurred at 8501000 µmol m2s1 although light compensation points (611 µmolm2s1) and chlorophyll a: b ratios (1.3) were low.While CO2 and PAR responses were obtained using varying numbersof sections with a constant fresh weight, the relationshipsbetween photosynthetic capacity and CO2 supply or PAR were maintainedwhen the data were expressed on a chlorophyll basis. It is concludedthat under low PAR, CO2 concentrating mechanisms interact inintact plants to maintain saturating CO2 levels within leaflacunae, although the responses of the various components ofCO2 supply to PAR require further investigation. Key words: Key words-Uttorella uniflora, internal CO2 concentration, crassulacean acid metabolism, root inorganic carbon supply, CO2 concentrating mechanism 相似文献
17.
Biochemical Limitations to Carbon Assimilation in C3 Plants--A Retrospective Analysis of the A/Ci Curves from 109 Species 总被引:9,自引:0,他引:9
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 m2 s1 for the coniferousspecies Picea abies to 194µmol m2 s1 forthe agricultural species Beta vulgaris, and averaged 64µmolm2 s1 across all species. The maximum rate ofelectron transport, Jmax, ranged from 17µmol m2s1 again for Picea abies to 372µmol m2 s1for the desert annual Malvastrum rotundifolium, and averaged134µmol m2 s1 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 µmolm2 s1 for the tropical perennial Tabebuia roseato 20·1 µmol m2 s1 for the weedyannual Xanthium strumarium, and averaged 10·1 µmolm2 s1 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 m2 s1, while for perennialsthese same two parameters averaged only 44 and 97 µmolm2 s1, 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
18.
Knight, S. L. and Mitchell, C. A. 1988. Effects of CO2 and photosyntheticphoton flux on yield, gas exchange and growth rate of Lactucasativa L. Waldmanns Green'.J. exp. Bot.39: 317328. Enrichment of CO2 to 46 mmol m3 (1 000 mm3 dm3)at a moderate photosynthetic photon flux (PPF) of 450 µmolm2 s1 stimulated fresh and dry weight gain oflettuce leaves 39% to 75% relative to plants at 16 mmol m3CO2 (350 mm3 dm3). Relative growth rate (RGR) was stimulatedonly during the first several days of exponential growth. ElevatingCO2 above 46 mmol m3 at moderate PPF had no further benefit.However, high PPF of 880900 µmol m2 s1gave further, substantial increases in growth, RGR, net assimilationrate (NAR) and photosynthetic rate (Pn), but a decrease in leafarea ratio (LAR), at 46 or 69 mmol m3 (1000 or 1500 mm3dm3) CO2, the differences being greater at the higherCO2 level. Enrichment of CO2 to a supraoptimal level of 92 mmolm3 (2000 mm3 dm3) at high PPF increased leaf areaand LAR, decreased specific leaf weight, NAR and Pn and hadno effect on leaf, stem and root dry weight or RGR relativeto plants grown at 69 mmol m3 CO2 after 8 d of treatment.The results of the study indicate that leaf lettuce growth ismost responsive to a combination of high PPF and CO2 enrichmentto 69 mmol m3 for several days at the onset of exponentialgrowth, after which optimizing resources might be conserved. Key words: Photosynthesis, relative growth rate, CO2 enrichment 相似文献
19.
Measurements of microclimate and photosynthesis of lucerne var.Europe were made in the field during the spring of 1976. Themaximum rate of canopy gross photosynthesis (14.3 g CO2 m2h1, I = ) was 2.5 times greater than that of S 24 perennialryegrass at the same LAI. This difference was due to differencesin individual leaf photosynthesis. The photosynthetic rate ofthe youngest fully expanded leaf of lucerne remained constantthroughout the experimental period at 3.6 g CO2 m2 h1(300 W m2). Measurements of soil water potential profiles indicated thatlucerne extracted water from the soil to a depth of at least800 mm, with a region of maximum uptake between 400 and 600mm. This capability, with a moderate mean leaf resistance of460 s m1, conferred a high assimilation efficiency onlucerne, with a mean water use efficiency of 34 g H2O lost pergram of carbohydrate assimilated, compared with 200 g H2O pergram of carbohydrate for S 24. Medicago sativa L, lucerne, photosynthesis, assimilation efficiency 相似文献
20.
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 m3, were provided to inoculated Trifolium repensgrowing in nutrient solution containing 7.13 mol m3 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 m3 (NH4)2SO4, at concentrations ranging from012 mol m3. MES at 9 mol m3 and 12 molm3 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