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1.
The influence of temperature on photosynthesis and transpirationwas studied in ten varieties of Lolium perenne, L. multiflorum,Dactylis glomerata, and Festuca arundinacea from three climaticorigins grown in three different controlled environments (15?C, 72 W m-2 visible irradiation, 16-h photoperiod; 25 ?C, 72W m-2 visible irradiation, 16-h photoperiod; and 25 ?C, 180W m-2 visible irradiation, 16-h photoperiod) and in the glasshousein July/August. The optimum temperature for photosynthesis was influenced primarilyby growth environment; growth at low temperature (15 ?C) resultedin a low optimum temperature, which differed little from varietyto variety. The maximum CO2-exchange rate was influenced bygrowth environment and by variety. Within a variety, plantsgrown at higher light intensity or lower temperature had a greaterCO2-exchange rate. Seven varieties showed a negative correlationbetween the optimum leaf temperature and the maximum CO2-exchangerate. Activation energies for photosynthesis were influencedby growth environment only. There were marked varietal differences in the values of leafresistances (ra + rt) obtained from transpiration data at theoptimum leaf temperature for CO2 exchange. In Lolium, and Dactylisthe Mediterranean varieties had higher leaf resistances thanthe Northern varieties with the maritime varieties intermediate.In general the Dactylis varieties had higher resistances thanthe corresponding Lolium and Festuca varieties. Only at highgrowth temperatures was (ra+rl) insensitive to temperature;otherwise an activation energy of about 10 kcal/mole was observed.A negative correlation was found between mean varietal diffusionresistances (ra+rl), and corresponding maximum CO2-exchangerates.  相似文献   

2.
The influence of elevated CO2 concentration (670 ppm) on thestructure, distribution, and patterning of stomata in Tradescantialeaves was studied by making comparisons with plants grown atambient CO2. Extra subsidiary cells, beyond the normal complementof four per stoma, were associated with nearly half the stomatalcomplexes on leaves grown in elevated CO2. The extra cells sharedcharacteristics, such as pigmentation and expansion, with thetypical subsidiary cells. The position and shape of the extrasubsidiary cells in face view differed in the green and purplevarieties of Tradescantia. Substomatal cavities of complexeswith extra subsidiary cells appeared larger than those foundin control leaves. Stomatal frequency expressed on the basisof leaf area did not differ from the control. Stomatal frequencybased on cell counts (stomatal index) was greater in leavesgrown in CO2-enriched air when all subsidiary cells were countedas part of the stomatal complex. This difference was eliminatedwhen subsidiary cells were included in the count of epidermalcells, thereby evaluating the frequency of guard cell pairs.The extra subsidiary cells were, therefore, recruited from theepidermal cell population during development. Stomatal frequencyin plants grown at elevated temperature (29 C) was not significantlydifferent from that of the control (24 C). The linear aggregationsof stomata were similar in plants grown in ambient and elevatedCO2. Since enriched CO2 had no effect on the structure or patterningof guard cells, but resulted in the formation of additionalsubsidiary cells, it is likely that separate and independentevents pattern the two cell types. Plants grown at enrichedCO2 levels had significantly greater internode lengths, butleaf area and the time interval between the appearance of successiveleaves were similar to that of control plants. Porometric measurementsrevealed that stomatal conductance of plants grown under elevatedCO2 was lower than that of control leaves and those grown atelevated temperature. Tradescantia was capable of regulatingstomatal conductance in response to elevated CO2 without changingthe relative number of stomata present on the leaf. Key words: Elevated CO2, stomata, subsidiary cells, patterning  相似文献   

3.
We examined changes in dry weight and leaf area within Dactylisglomerata L. plants using allometric analysis to determine whetherobserved patterns were truly affected by [CO2] and N supplyor merely reflect ontogenetic drift. Plants were grown hydroponicallyat four concentrations of in controlled environment cabinets at ambient (360 µll–1) or elevated (680 µl l–1) atmospheric[CO2]. Both CO2and N enrichment stimulated net dry matter production.Allometric analyses revealed that [CO2] did not affect partitioningof dry matter between shoot and root at high N supply. However,at low N supply there was a transient increase in dry matterpartitioning into the shoot at elevated compared to ambient[CO2] during early stages of growth, which is inconsistent withpredictions based on optimal partitioning theory. In contrast,dry matter partitioning was affected by N supply throughoutontogeny, such that at low N supply dry matter was preferentiallyallocated to roots, which is in agreement with optimal partitioningtheory. Independent of N supply, atmospheric CO2enrichment resultedin a reduction in leaf area ratio (LAR), solely due to a decreasein specific leaf area (SLA), when plants of the same age werecompared. However, [CO2] did not affect allometric coefficientsrelating dry weight and leaf area, and effects of elevated [CO2]on LAR and SLA were the result of an early, transient stimulationof whole plant and leaf dry weight, compared to leaf area production.We conclude that elevated [CO2], in contrast to N supply, changesallocation patterns only transiently during early stages ofgrowth, if at all. Copyright 2000 Annals of Botany Company Allometric growth, carbon dioxide enrichment, Cocksfoot, Dactylis glomerata L., dry weight partitioning, leaf area ratio, nitrogen supply, shoot:root ratio, specific leaf area  相似文献   

4.
Short-term effects of elevated CO2 during the early life phaseof plants may have long lasting consequences for growth andbiomass in later periods. We exposed hydroponically grown wheatseedlings to 5 d pulses of elevated CO2 while leaf expansiongrowth as well as shoot and root gas exchange were measuredsimultaneously and continuously. Shoot photosynthesis, night-timeshoot respiration and below-ground respiration (largely by roots)roughly doubled when atmospheric CO2 concentration was doubled.An interruption of CO2 enrichment caused CO2 assimilation andrespiration to return to control levels. However, while theresponse of photosynthesis was immediate, that of respirationshowed a hysteresis of about 3 d. Since shoot biomass increasedat elevated CO2 (with no change in allocation pattern) equalfluxes per shoot or root system after a return to control CO2concentrations indicate substantial downward adjustment of thecapacity for CO2 fixation and release in high-CO2 grown plants.Leaf expansion growth was completely unaffected by CO2 enrichment,whereas tiller initiation was significantly increased (doubledin 18 d). We conclude that leaf growth in these wheat plantswas already carbon-saturated at ambient CO2 concentration atoptimum mineral nutrient supply. The stimulation of growth ofwhole plants was exclusively due to enhanced tillering duringthis very early part of the life of these wheat plants. Key words: Allocation, atmospheric carbon dioxide enrichment, growth, photosynthesis, respiration, tillering, Triticum aestivum  相似文献   

5.
Tomato plants were grown in solution culture in a controlledenvironment at 20 ?C with a 12 h photoperiod of 400 µmolquanta m–2 s–1 PAR with either normal ambient CO2,approximately 340 vpm, or with 1000 vpm CO2. The short- andlong-term effects of CO2 enrichment on photosynthesis were determinedtogether with the levels of ribulose-1, 5-bisphosphate carboxylase(RuBPco) E.C. 4.1.1.39 [EC] protein and activity throughout leafdevelopment of the unshaded 5th leaf above the cotyledons. Thehigh CO2 concentration during growth did not appreciably affectthe rate of leaf expansion or final leaf area but did increasethe fresh weight per unit area of leaf. With short-term CO2enrichment, i.e. only during the photosynthesis measurements,the light-saturated photosynthetic rate (Pmax) of young leavesdid not increase while those reaching full expansion more thandoubled their net rate of CO2 fixation. However, with longerterm CO2 enrichment, i.e. growing the crop in high CO2, theplants did not maintain this photosynthetic gain. While theCO2 concentration during growth did not affect the peak in Pmaxmeasured in 300 vpm CO2 or Pmax in 1000 vpm CO2, RuBPco proteinor its activity, the subsequent ontogenetic decline in theseparameters was greatly accelerated by the high CO2 treatment.Compared with plants grown in normal ambient CO2 the high CO2grown leaves, when almost fully expanded, contained only approximatelyhalf as much RuBPco protein and Pmax in 300 vpm CO2 and Pmaxin1000 vpm CO2 were similarly reduced. The loss of RuBPco proteinmay be a major factor associated with the accelerated fall inPmax since it was close to that predicted from the amount andkinetics of RuBPco assuming RuBP saturation. In the oldest leavesexamined grown in high CO2 additional factors may be limitingphotosynthesis since RuBPco kinetics marginally overestimatedPmax in 300 vpm CO2 and the initial slope of photosynthesisin response to intercellular CO2 was also less than expectedfrom the extractable RuBPco. Key words: Lycopersicon esculentum (Mill.) cv. Findon Cross, CO2 enrichment, acclimation to high CO2, photosynthesis, RuBPco protein and activity  相似文献   

6.
Rumex obtusifolius plants were grown for several months in daylitenvironment chambers (Solardomes) force-ventilated with aircontaining 350 or 600 µ;mol mol–1 C02. ElevatedCO2 was found to accelerate the natural ontogenic decline inphotosynthesis, but did not reduce leaf duration. In both CO2treatments photosynthetic rates declined progressively withincreasing leaf age, the decline being greater for plants grownin elevated C02 such that rates became lower than in ambientCO2. The degree of CO2-induced photosynthetic down-regulationas determined by A/C1 analysis was found to be dependent onleaf age. The major contribution to the decline in photosynthesiswas likely to be a reduction in Rubisco activity as changesin stomataland mesophyll limitations were small. Instantaneouswater use efficiency (WUE1) was greater for plants in elevatedCO2, but these values declined rapidly with leaf age, whereasin ambient CO2 values were always lower, but were maintainedfor longer. Growth analysis indicated an increased root:-shootratio for plants grown in elevated CO2, this occurring almostentirely as a result of increased root growth. Greater rootproliferation and increased WUE1, are characteristics whichshould give this persistent and troublesome weed an increasedcompetitive advantage under projected conditions of climatechange Key words: tusifoliu, elevated CO2, gas exchange, leaf age, senescence  相似文献   

7.
REY  ANA; JARVIS  PAUL G. 《Annals of botany》1997,80(6):809-816
A field experiment consisting of 18 birch trees grown in opentop chambers in ambient and elevated CO2concentrations was setup with the aim of testing whether the positive growth responseobserved in many short-term studies is maintained after severalgrowing seasons. We present the results of growth and biomassafter 4.5 years of CO2exposure, one of the longest studies sofar on deciduous tree species. We found that elevated CO2ledto a 58% increase in biomass at the end of the experiment. However,estimation of stem mass during the growing season showed thatelevated CO2did not affect relative growth rate during the fourthgrowing season, and therefore, that the large accumulation ofbiomass was the result of an early effect on relative growthrate in previous years. Trees grown in elevated CO2investedmore carbon into fine roots and had relatively less leaf areathan trees grown in ambient CO2. In contrast with previous studies,acceleration of growth did not involve a significant declinein nutrient concentrations of any plant tissue. It is likelythat increased fine root density assisted the trees in meetingtheir nutrient demands. Changes in the species composition ofthe ectomycorrhizal fungi associated with the trees grown inelevated CO2in favour of late successional species supportsthe hypothesis of an acceleration of the ontogeny of the treesin elevated CO2.Copyright 1997 Annals of Botany Company Betula pendula; silver birch; elevated CO2; growth; biomass allocation; ectomycorrhizas; tissue composition; nutrients; leaf morphology; specific leaf area; stomatal density; shoot structure  相似文献   

8.
Plants of Phaseolus vulgaris were grown from seed in open-topgrowth chambers at the present (P, 350 µmol mol–1)atmospheric CO2 concentration and at an elevated (E, 700 µmolmol–1) CO2 concentration, and at low (L, without additionalnutrient solution) and high (H, with additional nutrient solution)nutrient supply for 28 d The effects of CO2 and nutrient availabilitywere examined on growth, morphological and biochemical characteristics Leaf area and dry mass were significantly increased by CO2 enrichmentand by high nutrient supply Stomatal density, stomatal indexand epidermal cell density were not affected by elevated CO2concentration or by nutrient supply Leaf thickness respondedpositively to CO2 increasing particularly in mesophyll areaas a result of cell enlargement Intercellular air spaces inthe mesophyll decreased slightly in plants grown in elevatedCO2 Leaf chlorophyll content per unit area or dry mass was significantlylower in elevated CO2 grown plants and increased significantlywith increasing nutrient availability The content of reducingcarbohydrates of leaves, stem, and roots was not affected byCO2 but was significantly increased by nutrient addition inall plant parts Starch content in leaves and stem was significantlyincreased by elevated CO2 concentration and by high nutrientsupply Phaseolus vulgaris, elevated atmospheric CO2, CO2-nutrient interaction, stomatal density, leaf anatomy, chlorophyll, carbohydrates, starch  相似文献   

9.
The carbon balance and changes in leaf structure in Clusia minorL., were investigated in controlled conditions with regardto nitrogen supply and responses to low and high photosyntheticallyactive radiation (PAR). Nitrogen deficiency and high PAR ledto the production of smaller leaves with higher specific leafdry weight (SLDW) and higher leaf water content, but with lowerchlorophyll content. Nitrogen and PAR levels at growth alsoaffected CO2 exchange and leaf area. In – N conditions,total daily net CO2 uptake and leaf area accumulation were slightlyless for high-PAR-grown plants. In contrast, high-PAR-grownplants supplied with nitrogen showed about a 4-fold higher totaldaily CO2 uptake and about twice the total leaf area of low-PAR-grownplants. Although total daily net CO2 uptake of +N plants wasonly slightly higher than –N plants under the low PARlevel, –N plants produced almost three times more leafarea but with lower SLDW. Under well-watered conditions, low-PAR-grownplants showed only CO2 evolution during the night and malicacid levels decreased. However, there was considerable night-timeaccumulation of titratable protons due to day/night changesin citric acid levels. High-PAR-grown plants showed net CO2uptake, malate and citrate accumulation during the dark period.However, most of the CO2 fixed at night probably came from respiratoryCO2. Positive night-time CO2 exchange was readily observed forlow-PAR-grown plants when they were transferred to high PARconditions or when they were submitted to water stress. In plantsgrown in high and low PAR, CAM leads to a substantial increasein daily water use efficiency for water-stressed plants, althoughtotal net CO2 uptake decreased.  相似文献   

10.
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   

11.
Single, seed-grown plants of ryegrass (Lolium perenne L. cv.Melle) were grown for 49 d from the early seedling stage ingrowth cabinets at a day/night temperature of 20/15 C, witha 12 h photoperiod, and a CO2 concentration of either 340 or680µI 1–1 CO2. Following complete acclimation tothe environmental regimes, leaf and whole plant CO2 effluxesand influxes were measured using infra-red gas analysis techniques.Elevated CO2 increased rates of photosynthesis of young, fullyexpanded leaves by 35–46% and of whole plants by morethan 50%. For both leaves and whole plants acclimation to 680µI–1 CO2 reduced rates of photosynthesis in bothCO2 regimes, compared with plants acclimated to 340µll–1. There was no significant effect of CO2 regime onrespiration rates of either leaves or whole plants, althoughleaves developed in elevated CO2 exhibited generally lower ratesthan those developed in 340µI I–1 CO2. Initially the seedling plants in elevated CO2 grew faster thantheir counterparts in 340µI I–1 CO2, but this effectquickly petered out and final plant weights differed by onlyc. 10%. Since the total area of expanded and unexpanded laminaewas unaffected by CO2 regime, specific leaf area was persistently13–40% lower in elevated CO2 while, similarly, root/shootratio was also reduced throughout the experiment. Elevated CO2reduced tissue nitrogen contents of expanded leaves, but hadno effect on the nitrogen contents of unexpanded leaves, sheathsor roots. The lack of a pronounced effect of elevated CO2 on plant growthwas primarily due to the fact that CO2 concentration did notinfluence tiller (branch) numbers. In the absence of an effecton tiller numbers, any possible weight increment was restrictedto the c. 2.5 leaves of each tiller. The reason for the lackof an effect on tillering is not known. Key words: Lolium perenne, ryegrass, elevated CO2, photosynthesis, respiration, growth, development  相似文献   

12.
Two common tallgrass prairie species, Andropogon gerardii, thedominant C4 grass in this North American grassland, and Salviapitcheri, a C3 forb, were exposed to ambient and elevated (twiceambient) CO2 within open-top chambers throughout the 1993 growingseason. After full canopy development, stomatal density on abaxialand adaxial surfaces, guard cell length and specific leaf mass(SLM; mg cm-2) were determined for plants in the chambers aswell as in adjacent unchambered plots. Record high rainfallamounts during the 1993 growing season minimized water stressin these plants (leaf xylem pressure potential was usually >-1·5 MPa in A. gerardii) and also minimized differencesin water status among treatments. In A. gerardii, stomatal densitywas significantly higher (190 ± 7 mm-2; mean ±s.e.) in plants grown outside of the chambers compared to plantsthat developed inside the ambient CO2 chambers (161 ±5 mm-2). Thus, there was a significant 'chamber effect' on stomataldensity. At elevated levels of CO2, stomatal density was evenlower (P < 0·05; 121 ± 5 mm-2). Most stomatawere on abaxial leaf surfaces in this grass, but the ratio ofadaxial to abaxial stomatal density was greater at elevatedlevels of CO2. In S. pitcheri, stomatal density was also significantlylower when plants were grown in the open-top chambers (235 ±10 mm-2 outside vs. 140 ± 6 mm-2 in the ambient CO2 chamber).However, stomatal density was greater at elevated CO2 (218 ±12 mm-2) compared to plants from the ambient CO2 chamber. Theratio of stomata on adaxial vs. abaxial surfaces did not varysignificantly in this herb. Guard cell lengths were not significantlyaffected by growth in the chambers or by elevated CO2 for eitherspecies. Growth within the chambers resulted in lower SLM inS. pitcheri, but CO2 concentration had no effect. In A. gerardii,SLM was lower at elevated CO2. These results indicate that stomataland leaf responses to elevated CO2 are species specific, andreinforce the need to assess chamber effects along with treatmenteffects (CO2) when using open-top chambers.Copyright 1994, 1999Academic Press Andropogon gerardii, elevated CO2, Salvia pitcheri, stomatal density, tallgrass prairie  相似文献   

13.
The effects of elevated atmospheric CO2, alone or in combinationwith water stress, on stomatal frequency in groundnut (Arachishypogaea (L.) cv. Kadiri-3) were investigated. CO2 exerted significanteffects on stomatal frequency only in irrigated plants. Theeffects of drought on leaf development out weighed the smallereffects of CO2 concentration, although reductions in stomatalfrequency induced by elevated atmo-spheric CO2 were still observed.When stands of groundnut were grown under irrigated conditionswith unrestricted root systems, an increase in atmospheric CO2from 375 to 700 ppmv decreased stomatal frequency on both leafsurfaces by up to 16% in droughted plants, stomatal frequencywas reduced by 8% on the adaxial leaf surface only. Elevatedatmospheric CO2 promoted larger reductions in leaf conductancethan the changes in stomatal frequency, indicating partial stomatalclosure. As a result, the groundnut stands grown at elevatedCO2 utilized the available soil moisture more slowly than thosegrown under ambient CO2, there by extending the growing period.Despite the large variations in cell frequencies induced bydrought, there was no treatment effect on either stomatal indexor the adaxial/abaxial stomatalfrequency ratio. The data suggestthat the effects of future increases in atmospheric CO2 concentrationon stomatal frequency in groundnut are likely to be small, especiallyunder conditions of water stress, but that the combination ofassociated reductions in leaf con-ductance and enhanced assimilationat elevated CO2 will be important in semi-arid regions Key words: Arachis hypogaea L, Leguminosae, groundnu, stomatal frequency, CO2, drought  相似文献   

14.
Both fast and slow chlorophyll fluorescence kinetics were usedto assess the differential heat sensitivity of ten wheat (Triticumaestivum L.) varieties commonly grown in northern, temperateor (sub-) tropical climate zones. No consistent differencesbetween the groups were found. Studies on the role of growthtemperature in modulating the response of photosynthesis toheat stress were carried out on two of the varieties, APU (Finnish)and K65 (Indian), the former being more sensitive to heat stress.Growth and development of these varieties were similar underboth cool (13 °C day, 10 °C night) and warm (30 °Cday, 25 °C night), regimes. The cool-grown plants exhibitedhigher rates of net CO2 exchange than the warm-grown plantswhen expressed on a chlorophyll basis and, in both regimes,photosynthesis declined with age prior to reduction in chlorophyllcontent. Net CO2 exchange in leaves of K65 showed greater sensitivityto short-term heat stress than APU when plants were grown underthe cool regime. Plants grown under the warm regime exhibitedan upward shift in the optimum temperature for net CO2 exchangein both varieties, with K65 showing somewhat superior performanceat high temperature compared with APU. Stomatal aperture wasessentially unaffected by assay temperature during these measurements. Key words: CO2 exchange, growth temperature, Triticum aestivum  相似文献   

15.
The effect of exposure to elevated CO2 on the processes of leafcell production and leaf cell expansion was studied using primaryleaves of Phaseolus vulgaris L. Cell division and expansionwere separated temporally by exposing seedlings to dim red lightfor 10 d (when leaf cell division was completed) followed byexposure to bright white light for 14 d (when leaf growth wasentirely dependent on cell expansion). When plants were exposedto elevated CO2 during the phase of cell expansion, epidermalcell size and leaf area development were stimulated. Three piecesof evidence suggest that this occurred as a result of increasedcell wall loosening and extensibility, (i) cell wall extensibility(WEx, measured as tensiometric extension using an Instron) wassignificantly increased, (ii) cell wall yield turgor (V, MPa)was reduced and (iii) xyloglucan endotransglycosylase (XET)enzyme activity was significantly increased. When plants wereexposed to elevated CO2 during the phase of cell division, thenumber of epidermal cells was increased whilst final cell sizewas significantly reduced and this was associated with reducedfinal leaf area, WEx and XET activity. When plants were exposedto elevated CO2 during both phases of cell division and expansion,leaf area development was not affected. For this treatment,however, the number of epidermal cells was increased, but cellexpansion was inhibited, despite exposure to elevated CO2 duringthe expansion phase. Assessments were also made of the spatialpatterns of WEx across the expanding leaf lamina and the datasuggest that exposure to elevated CO2 during the phase of leafexpansion may lead to enhanced extensibility particularly atbasal leaf margins which may result in altered leaf shape. The data show that both cell production and expansion were stimulatedby elevated CO2, but that leaf growth was only enhanced by exposureto elevated CO2 in the cell expansion phase of leaf development.Increased leaf cell expansion is, therefore, an important mechanismfor enhanced leaf growth in elevated CO2, whilst the importanceof increased leaf cell production in elevated CO2 remains tobe elucidated. Key words: Phaseolus vulgaris L., dwarf beans, elevated CO2, biophysics of cell expansion, xyloglucan endotransglycosylase, XET, water relations  相似文献   

16.
Pascopyrum smithii (C3) andBouteloua gracilis (C4) are importantforage grasses native to the Colorado shortgrass steppe. Thisstudy investigated photosynthetic responses of these grassesto long-term CO2enrichment and temperature in relation to leafnonstructural carbohydrate (TNC) and [N]. Glasshouse-grown seedlingswere transferred to growth chambers and grown for 49 d at twoCO2concentrations (380 and 750 µmol mol-1) at 20 and 35°C, and two additional temperatures (25 and 30 °C) at750 µmol mol-1CO2. Leaf CO2exchange rate (CER) was measuredat a plant's respective growth temperature and at two CO2concentrationsof approx. 380 and 700 µmol mol-1. Long-term CO2enrichmentstimulated CER in both species, although the response was greaterin the C3,P. smithii . Doubling the [CO2] from 380 to 750 µmolmol-1stimulated CER ofP. smithii slightly more in plants grownand measured at 30 °C compared to plants grown at 20, 25or 35 °C. CO2-enriched plants sometimes exhibited lowerCER when compared to ambient-grown controls measured at thesame [CO2], indicating photosynthetic acclimation to CO2growthregime. InP. smithii , such reductions in CER were associatedwith increases in TNC and specific leaf mass, reductions inleaf [N] and, in one instance, a reduction in leaf conductancecompared to controls. InB. gracilis , photosynthetic acclimationwas observed more often, but significant changes in leaf metabolitelevels from growth at different [CO2] were generally less evident.Temperatures considered optimal for growth (C3: 20 °C; C4:35 °C) sometimes led to CO2-induced accumulations of TNCin both species, with starch accumulating in the leaves of bothspecies, and fructans accumulating only inP. smithii. Photosynthesisof both species is likely to be enhanced in future CO2-enrichedand warmer environments, although responses will sometimes beattenuated by acclimation. Acclimation; blue grama (Bouteloua gracilis (H.B.K.) Lag ex Steud.); leaf nitrogen concentration; nonstructural carbohydrates; photosynthesis; western wheatgrass (Pascopyrum smithii (Rydb.) Love)  相似文献   

17.
Net photosynthesis rate (Pn), stomatal conductance to CO2 andresidual conductance to CO2 were measured in the last six leaves(the sixth or flag leaf and the preceding five leaves) of Triticumaestivum L. cv. Kolibri plants grown in Mediterranean conditions.Recently fully expanded leaves of well-watered plants were alwaysused. Measurements were made at saturating photosynthetic photonflux density, and at ambient CO2 and O2 levels. The specificleaf area, total organic nitrogen content, some anatomical characteristics,and other parameters, were measured on the same leaves usedfor gas exchange experiments. A progressive xeromorphic adaptation in the leaf structure wasobserved with increasing leaf insertion levels. Furthermore,mesophyll cell volume per unit leaf area (Vmes/A) decreasedby 52·6% from the first leaf to the flag leaf. Mesophyllcell area per unit leaf area also decreased, but only by 24·5%.However, nitrogen content per unit mesophyll cell volume increasedby 50·6% from the first leaf to the flag leaf. This increasecould be associated to an observed higher number of chloroplastcross-sections per mm2 of mesophyll cell cross-sectional areain the flag leaf: values of 23000 in the first leaf and 48000in the flag leaf were obtained. Pn per unit leaf area remainedfairly constant at the different insertion levels: values of33·83±0·93 mg dm–2 h–1 and32·32±1·61 mg dm–2 h–1 wereobtained for the first leaf and the flag leaf, respectively.Residual conductance, however, decreased by 18·2% fromthe first leaf to the flag leaf. Stomatal conductance increasedby 41·7%. The steadiness in Pn per unit leaf area across the leaf insertionlevels could be mainly accounted for by an opposing effect betweena decrease in Vmes/A and a more closely packed arrangement ofphotosynthetic apparatus. Adaptative significance of structuralchanges with increasing leaf insertion levels and the steadinessin Pn per unit leaf area was studied. Key words: Photosynthesis, structure, wheat  相似文献   

18.
Seedlings of Maranthes corymbosa (Blume) and Eucalyptus tetrodonta(F. Muell) were grown with or without CO2 enrichment (700µmolCO2 mol–1 The response of stomatal conductance (g2) toleaf drying, exogenous absclslc acid and calcium ions was investigatedin M. corymbosa. Reciprocal transfer experiments were also conductedwhereby plants were grown in one treatment and then transferredto the other before g, was measured. Stomatal conductance in M. corymbosa was more sensitive (a greaterpercentage decline in g2 per unit percentage decline in leaffresh weight) to leaf water status under conditions of CO2 enrichmentcompared to ambient conditions. However, the rate of reductionof g2 in response to exogenous abscisic acid was not influencedby CO2 treatment. In contrast, the rate of reduction of g2,in response to exogenous CaCl2 was decreased under conditionsof CO2 enrichment. Reciprocal transfer experiments showed that expo sure to CO2enrichment results in a short-term, reversible decline in g2,as a result of decreased stomatal aperture and a long-term,irreversible decline in g2 as a result of a decreased stomataldensity. Seedlings of E. tetrodonta were used to investigate the responseof g2 to light flux density, leaf-to-air vapour pressure difference(LAVPD), leaf internal CO2 concentration (C1 and temperature.Reciprocal transfer experiments were also conducted. CO2 enrichmentdid not influence the pattern or sensitivity of response ofg to LAVPD and C in E. tetrodonta. In contrast, the slope ofthe response of g2, to temperature decreased for trees grownunder elevated [CO2]a conditions and the equilibrium g2 attainedat saturating light was also decreased for plants grown underelevated [CO2a. conditions. Key words: Stomata, elevated CO2, tropical trees  相似文献   

19.
Photosynthetic rates of outdoor-grown soybean (Glycine max L.Merr. cv. Bragg) canopies increased with increasing CO2 concentrationduring growth, before and after canopy closure (complete lightinterception), when measured over a wide range of solar irradiancevalues. Total canopy leaf area was greater as the CO2 concentrationduring growth was increased from 160 to 990 mm3 dm–3.Photosynthetic rates of canopies grown at 330 and 660 mm3 CO2dm–3 were similar when measured at the same CO2 concentrationsand high irradiance. There was no difference in ribulose bisphosphatecarboxylase/oxygenase (rubisco) activity or ribulose 1,5-bisphosphate(RuBP) concentration between plants grown at the two CO2 concentrations.However, photosynthetic rates averaged 87% greater for the canopiesgrown and measured at 660 mm3 CO2 dm–3. A 10°C differencein air temperature during growth resulted in only a 4°Cleaf temperature difference, which was insufficient to changethe photosynthetic rate or rubisco activity in canopies grownand measured at either 330 or 660 mm3 CO2 dm–3. RuBP concentrationsdecreased as air temperature during growth was increased atboth CO2 concentrations. These data indicate that the increasedphotosynthetic rates of soybean canopies at elevated CO2 aredue to several factors, including: more rapid development ofthe leaf area index; a reduction in substrate CO2 limitation;and no downward acclimation in photosynthetic capacity, as occurin some other species. Key words: CO2 concentration, soybean, canopy photosynthesis  相似文献   

20.
To examine the effects of a doubled atmospheric CO2 concentrationand other aspects of global climate change on a common CAM speciesnative to the Sonoran Desert, Agave deserti was grown under370 and 750 µmol CO2 mol–1 air and gas exchangewas measured under various environmental conditions. Doublingthe CO2 concentration increased daily net CO2 uptake by 49%throughout the 17 months and decreased daily transpiration by24%, leading to a 110% increase in water-use efficiency. Underthe doubled CO2 concentration, the activity of ribulose-1,5-bisphosphatecarboxylase/oxygenase (Rubisco) was 11% lower, phosphoenolpyruvatecarboxylase was 34% lower, and the activated:total ratio forRubisco was 25% greater than under the current CO2 concentration.Less leaf epicuticular wax occurred on plants under the doubledCO2 concentration, which decreased the reflectance of photosyntheticphoton flux (PPF); the chlorophyll content per unit leaf areawas also less. The enhancement of daily net CO2 uptake by doublingthe CO2 concentration increased when the PPF was decreased below25 mol m–2 d–1 when water was withheld, and whenday/night temperatures were below 17/12 C. More leaves, eachwith a greater surface area, were produced per plant under thedoubled CO2 concentration. The combination of increased totalleaf surface area and increased daily net CO2 uptake led toan 88% stimulation of dry mass accumulation under the doubledCO2 concentration. A rising atmospheric CO2 concentration, togetherwith accompanying changes in temperature, precipitation, andPPF, should increase growth and productivity of native populationsof A. deserti. Key words: Crassulacean acid metabolism, gas exchange, global climate change, Sonoran Desert  相似文献   

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