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1.
The hypothesis that net photosynthesis is diminished in many plant species because of a high rate of CO 2 evolution in the light has been tested further. High rates of CO 2 output in CO 2-free air in comparison with dark respiration were found in Chlamydomonas reinhardi, wheat leaves, tomato leaves, and to a lesser extent in Chlorella pyrenoidosa by means of the 14C-photorespiration assay. In tobacco leaves high photorespiration was characteristic of a standard variety, Havana Seed, and a possibly still higher rate was found in a yellow heterozygous mutant, JWB Mutant. However, the dark homozygous sibling of the latter, JWB Wild, had a low photorespiration for the tobacco species. The relative rates of photorespiration were in the same sequence when measured by the 14CO 2 released in normal air from leaf disks supplied with glycolate-1- 14C in the light. As would be predicted by the hypothesis, the maximal net rate of photosynthesis at 300 ppm of CO2 in the air in JWB Wild leaves was greater (24%) than in Havana Seed, while JWB Mutant had less CO2 uptake than the standard variety (21%). At 550 ppm of CO2 the differences in net photosynthesis were not as great between the 2 siblings as at 200 ppm. The relative leaf expansion rates of seedlings of the 3 tobacco varieties in a greenhouse had the same relationship as their rates of CO2 assimilation. Thus within the tobacco species, as in a comparison between tobacco and maize, low photorespiratory CO2 evolution was correlated with higher photosynthetic efficiency. Therefore it seems that increased CO2 uptake should be achieved by genetic interference with the process of photorespiration. 相似文献
2.
We found similarities between the effects of low night temperatures (5°C–10°C) and slowly imposed water stress on photosynthesis in grapevine ( Vitis vinifera L.) leaves. Exposure of plants growing outdoors to successive chilling nights caused light- and CO 2-saturated photosynthetic O 2 evolution to decline to zero within 5 d. Plants recovered after four warm nights. These photosynthetic responses were confirmed in potted plants, even when roots were heated. The inhibitory effects of chilling were greater after a period of illumination, probably because transpiration induced higher water deficit. Stomatal closure only accounted for part of the inhibition of photosynthesis. Fluorescence measurements showed no evidence of photoinhibition, but nonphotochemical quenching increased in stressed plants. The most characteristic response to both stresses was an increase in the ratio of electron transport to net O 2 evolution, even at high external CO 2 concentrations. Oxygen isotope exchange revealed that this imbalance was due to increased O 2 uptake, which probably has two components: photorespiration and the Mehler reaction. Chilling- and drought-induced water stress enhanced both O 2 uptake processes, and both processes maintained relatively high rates of electron flow as CO 2 exchange approached zero in stressed leaves. Presumably, high electron transport associated with O 2 uptake processes also maintained a high ΔpH, thus affording photoprotection. 相似文献
3.
Photorespiration has been indicated as an important mechanism for maintaining CO 2 assimilation and alleviating photodamage under conditions of high light and low CO 2. We tested the hypothesis that plants grown under a high temperature had greater electron flow for photorespiration compared with those grown under a relative low temperature. Responses of photosynthetic electron flow and CO 2 assimilation to incident light intensity and intercellular CO 2 concentration were examined in leaves of tobacco cultivar ‘k326’. Plants were cultivated at three sites with different ambient temperatures (Zhengzhou, Zunyi and Jiangchuan). Under high light, plants grown in Zhengzhou (with the highest growth temperature in the three sites) showed higher effective quantum yield of photosystem II and total electron flow through photosystem II than that in Zunyi and Jiangchuan. However, regardless of light intensity and intercellular CO 2 status, there were no significant differences among sites in the photosynthetic CO 2 assimilation rate or electron flow devoted to the carboxylation of ribulose‐1,5‐bisphosphate (RuBP). As a result, plants grown at high temperature showed higher electron flow devoted to oxygenation of RuBP than plants grown at low temperature. These results suggested that enhancement of electron flow for photorespiration is an important strategy in tobacco for acclimating to high growth temperature. 相似文献
4.
As leaf irradiance is decreased in increments, a single transient CO 2 burst is exhibited by C 3 plant leaves. This post-lower illumination CO 2 burst (PLIB) is sensitive to changes in irradiance, to changes in the concentrations of O 2 and CO 2, and to temperature. Increasing O 2 concentrations above ambient produces a progressively larger PLIB while increasing CO 2 concentrations above ambient produces a progressively smaller PLIB. The PLIB, which exhibits many responses to environment common with other methods for measuring photorespiration and photosynthesis, is proposed as a measure of photorespiration in illuminated leaves of C 3 plants. Although the PLIB cannot be used as a quantitative measurement of photorespiration, we propose that the PLIB is a rapid, easy, relatively inexpensive, nondestructive method for evaluating photorespiration in intact illuminated C 3 leaves in air. 相似文献
5.
Leaf photosynthesis of the sensitive plant Mimosa pudica displays a transient knockout in response to electrical signals induced by heat stimulation. This study aims at clarifying the underlying mechanisms, in particular, the involvement of respiration. To this end, leaf gas exchange and light reactions of photosynthesis were assessed under atmospheric conditions largely eliminating photorespiration by either elevated atmospheric CO 2 or lowered O 2 concentration (i.e. 2000 μmol mol ?1 or 1%, respectively). In addition, leaf gas exchange was studied in the absence of light. Under darkness, heat stimulation caused a transient increase of respiratory CO 2 release simultaneously with stomatal opening, hence reflecting direct involvement of respiratory stimulation in the drop of the net CO 2 uptake rate. However, persistence of the transient decline in net CO 2 uptake rate under illumination and elevated CO 2 or 1% O 2 makes it unlikely that photorespiration is the metabolic origin of the respiratory CO 2 release. In conclusion, the transient knockout of net CO 2 uptake is at least partially attributed to an increased CO 2 release through mitochondrial respiration as stimulated by electrical signals. Putative CO 2 limitation of Rubisco due to decreased activity of carbonic anhydrase was ruled out as the photosynthesis effect was not prevented by elevated CO 2. 相似文献
6.
A transient CO 2 burst is exhibited by irradiated leaves of the C 3 plant geranium ( Pelargonium X hortorum, Bailey) after the irradiance is quickly lowered. The light CO 2 burst appears to be related to photorespiration because of its irradiance dependency and its sensitivity to other environmental components such as CO 2 and O 2 concentration. The term post-lower-irradiance CO 2 burst or PLIB is used to describe the phenomenon. The PLIB appears to be a quantitative measurement of photorespiration with intact geranium leaves. The PLIB has been observed with intact leaves of other C 3 plants but not with C 4 leaves. Therefore, it is proposed that, after maximizing intact leaf photosynthetic rates and leaf chamber gas measuring conditions, photorespiration can be measured with intact C 3 leaves such as geranium as a transient post-lower-irradiance CO 2 burst. 相似文献
7.
The photosynthetic gas-exchange has been assessed traditionally either as O 2 evolution or CO 2 consumption. In this study, we used a liquid-phase O 2 electrode combined with CO 2 optodes to examine simultaneously photosynthesis in intact leaves of mangrove Rhizophora mucronata. We verified suitable conditions for leaf photosynthetic rates by assessing pH levels and NaHCO 3 concentrations and compared these to the gas-exchange method at various PAR levels. The photosynthetic rate in response to pH exhibited a similar pattern both for O 2 evolution and CO 2 consumption, and higher rates were associated with intermediate pH compared with low and high pH values. The net photosynthetic quotient (PQ) of R. mucronata leaves ranged from 1.04–1.28. The PQ values, which were never lesser than 1, suggested that photorespiration did not occur in R. mucronata leaves under aqueous conditions. The similar maximum photosynthetic rates suggested that all measurements had a high capacity to adjust the photosynthetic apparatus under a light saturation condition. The simultaneous measurements of O 2 evolution and CO 2 consumption using the Clark oxygen electrode polarographic sensor with the CO 2 optode sensor provided a simple, stable, and precise measurement of PQ under aqueous and saturated light conditions. 相似文献
8.
Preincubation of illuminated tobacco ( Nicotiana tabacum L.) leaf disks in glycidate (2,3-epoxypropionate) or glyoxylate inhibited photorespiration by about 40% as determined by the ratio of 14CO 2 evolved into CO 2-free air in light and in darkness. However, under identical preincubation conditions used for the light/dark 14C assays, the compounds failed to reduce photorespiration or stimulate net photosynthesis in tobacco leaf disks based on other CO 2 exchange parameters, including the CO 2 compensation concentration in 21% O 2, the inhibitory effect of 21% O 2 on net photosynthesis in 360 microliters per liter of CO 2 and the rate of net photosynthetic 14CO 2 uptake in air. The effects of both glycidate and glyoxylate on the 14C assay are inconsistent with other measures of photorespiratory CO2 exchange in tobacco leaf disks, and thus these data question the validity of the light to dark ratio of 14CO2 efflux as an assay for relative rates of photorespiration (Zelitch 1968, Plant Physiol 43: 1829-1837). The results of this study specifically indicate that neither glycidate nor glyoxylate reduces photorespiration or stimulates net photosynthesis by tobacco leaf disks under physiological conditions of pO2 and pCO2, contrary to previous reports. 相似文献
9.
Prior illumination in CO 2-free air enhances a respiration from maize ( Zea mays L.) leaves different in onset and duration from the postillumination burst of photorespiration. The course of respiration after brief illumination of attached leaves was measured as CO 2 efflux in darkness into CO 2-free atmospheres with four O 2 concentrations. The peak of CO 2 efflux following illumination was suppressed by 2.23% O 2, was completely eliminated by 0.04% O 2, and was not stimulated by 40% O 2 compared with air. Compared with air, steady dark respiration was suppressed by 0.04% O 2 but was not affected by 2.23% nor 40% O 2. Excision and subsequent uptake of distilled water through the vascular system nearly eliminated the enhanced respiration. 相似文献
10.
Glycolate synthesis was inhibited 40–50% in illuminated tobacco leaf disks, which have rapid rates of photorespiration, when floated on 20 mm potassium glycidate (2,3-epoxypropionate), an epoxide similar in structure to glycolate. The inhibitor also decreased the release of photorespiratory CO 2 about 40%, and the specificity of glycidate was demonstrated by the 40–50% increase in rate of photosynthetic CO 2 uptake observed in its presence. The importance of glycolate synthesis and metabolism in the production of photorespiratory CO 2 and the role of glycolate in diminishing net photosynthesis in species with rapid rates of photorespiration was thus further confirmed. L-(or 2 S)-Glycidate was slightly more active than DL-glycidate, but glycidate was more effective as a specific inhibitor in leaf tissue than several other epoxide analogs of glycolate examined. The products of photosynthetic 14O 2 fixation after 3 or 4 min of uptake were proportionately altered in the presence of glycidate, and the specific radioactivity of the [ 14C]glycolate produced was closer to that of the 14CO 2 supplied. Glycidate inhibited glycolate synthesis in tobacco leaf disks irreversibly, since the degree of inhibition was the same for at least 2 hr after the inhibitor solution was removed. Glycidate also blocked glycolate synthesis in maize leaf disks, tissue with low rates of photorespiration, but large increases in net photosynthesis were not observed in maize with glycidate, because glycolate synthesis is normally only about 10% as rapid in maize as in tobacco. The demonstration of increases in net photosynthesis of 40–50% when glycolate synthesis (and photorespiration) is blocked with glycidate indicates in an independent manner that the biochemical or genetic control of photorespiration should permit large increases in plant productivity in plant species possessing rapid rates of photorespiration. 相似文献
11.
The postillumination transient of CO 2 exchange and its relation to photorespiration has been examined in leaf discs from tobacco ( Nicotiana tabacum) and maize ( Zea mays). Studies of the transients observed by infrared gas analysis at 1, 21, and 43% O 2 in an open system were extended using the nonsteady state model described previously (Peterson and Ferrandino 1984 Plant Physiol 76: 976-978). Cumulative CO 2 exchange equivalents ( i.e. nanomoles CO 2) versus time were derived from the analyzer responses of individual transients. In tobacco (C 3), subtraction of the time course of cumulative CO 2 exchange under photorespiratory conditions (21 or 43% O 2) from that obtained under nonphotorespiratory conditions (1% O 2) revealed the presence of an O 2-dependent and CO 2-reversible component within the first 60 seconds following darkening. This component was absent in maize (C 4) and at low external O 2:CO 2 ratios ( i.e. <100) in tobacco. The size of the component in tobacco increased with net photosynthesis as irradiance was increased and was positively associated with inhibition of net photosynthesis by O 2. This relatively simple and rapid method of analysis of the transient is introduced to eliminate some uncertainties associated with estimation of photorespiration based on the maximal rate of postillumination CO 2 evolution. This method also provides a useful and complementary tool for detecting variation in photorespiration. 相似文献
12.
Photosynthesis is a complex process whose rate is affected by many biochemical and biophysical factors. Fortunately, it is possible to determine, or at least estimate, many of the most important parameters using a combination of optical methods and gas transient analyses. We describe here a computer‐operated routine that has been developed to make detailed assessments of photosynthesis at a comprehensive level. The routine comprised the following measurements: steady‐state light and CO 2 response curves of net CO 2 assimilation at 21 and 2 kPa O 2; transients from limiting to different saturating CO 2 concentrations at 2 kPa O 2; post‐illumination CO 2 fixation transient; dark–light induction of O 2 evolution; O 2 yield from one saturating single‐turnover flash; chlorophyll fluorescence F0, Fs and Fm during the light and CO 2 response curves; leaf transmission at 820 nm (P700 +) during the light and CO 2 response curves; post‐illumination re‐reduction time of P700 +. The routine was executed on a two‐channel fast‐response gas exchange measurement system (A. Laisk and V. Oja: Dynamic Gas Exchange of Leaf Photosynthesis. CSIRO, Canberra, Australia). Thirty‐six intrinsic characteristics of the photosynthetic machinery were derived, including quantum yield of CO 2 fixation ( YCO2), time constant of P700 re‐reduction ( τ′), relative optical cross‐sections of PSII and PSI antennae ( aII, aI), PSII and PSI density per leaf area unit, plastoquinone pool, total mesophyll resistance, mesophyll diffusion resistance, Vm, Km(CO 2) and CO 2/O 2 specificity of Rubisco, RuBP pool at CO 2 limitation (assimilatory charge). An example of the routine and calculations are shown for one leaf and data are presented for leaves of 8‐year‐old‐trees of two birch clones growing in Suonenjoki Forest Research Station, Finland, during summer 2000. Parameters YCO2, basic τ′, aII, aI, Km(CO 2) and Ks varied little in different leaves [relative standard deviation (RSD) < 7%], other parameters scattered widely (RSD typically 10–40%). It is concluded that the little scattered parameters are determined by basic physico‐chemical properties of the photosynthetic machinery whereas the widely scattered parameters are adjusting to growth conditions. The proposed non‐destructive routine is suitable for diagnosing the photosynthetic machinery of leaves and may be applied in plant ecophysiology and in genetic engineering of plants. 相似文献
13.
Summary After 10 min illumination of segments of bean ( Phaseolus vulgaris L.) or maize ( Zea mays L.) leaves in air with 14CO 2, the atmosphere was changed to CO 2-free O 2 or N 2 and conversion of photosynthetic products in the light was investigated. The experiments have shown that after the 14CO 2 assimilation period the bean leaves contain the pool of weakly fixed 14C (WF- 14C) which is converted into stable products during the subsequent period of illumination in CO 2-free N 2. In O 2 atmosphere the WF- 14C pool is initially the main source of CO 2 evolved. The marked decrease in radioactivity of sucrose and starch during illumination of bean leaves in O 2 atmosphere indicates that these compounds were also the source of CO 2 evolved in the light. The total amount of previously fixed 14C remained almost on the same level during illumination of maize leaves in N 2 as well as in O 2. However, oxygen changed the distribution of 14C in photosynthetic products, which is suggested to be the consequence of the photorespiration process in maize.Abbreviation WF- 14C
weakly fixed 14C 相似文献
14.
Oxygen inhibition of photosynthesis and CO 2 evolution during photorespiration were compared in high CO 2-grown and air-grown Chlorella pyrenoidosa, using the artificial leaf technique at pH 5.0. High CO 2 cells, in contrast to air-grown cells, exhibited a marked inhibition of photosynthesis by O 2, which appeared to be competitive and similar in magnitude to that in higher C 3 plants. With increasing time after transfer to air, the photosynthetic rate in high CO 2 cells increased while the O 2 effect declined. Photorespiration, measured as the difference between 14CO 2 and 12CO 2 uptake, was much greater and sensitive to O 2 in high CO 2 cells. Some CO 2 evolution was also present in air-grown algae; however, it did not appear to be sensitive to O 2. True photosynthesis was not affected by O 2 in either case. The data indicate that the difference between high CO 2 and air-grown algae could be attributed to the magnitude of CO 2 evolution. This conclusion is discussed with reference to the oxygenase reaction and the control of photorespiration in algae. 相似文献
15.
The effect of leaf dehydration on photosynthetic O 2 exchange of potato ( Solanum tuberosum L., cv. Haig) leaf discs was examined using 18O 2 as a tracer and mass spectrometry. In normal air (350 μl·l ?1CO 2) and under an irradiance of 390 μmol photons·m ?2·s 1, a relative water deficit (RWD) of about 30% severely decreased net O 2 evolution and increased O 2 uptake by about 50%, thus indicating an enhancement of photorespiration. Increasing CO 2 concentrations diminished O 2 uptake and stimulated net O 2 evolution both in well-hydrated and in dehydrated (RWD of about 30%) leaves. Much higher CO 2 concentrations (up to 4%) were required to observe a complete effect of CO 2 in dehydrated leaves. The chloroplastic CO 2 concentration at the ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) level (C c) was calculated from O 2-exchange data in both well-hydrated and dehydrated leaves, assuming that the specificity factor of Rubisco was unaffected by desiccation. When plotting net O 2 photosynthesis as a function of C c, a similar relationship was obtained for well-hydrated and waterstressed leaf discs, thus showing that the main effect of water deficit is a decrease of the chloroplastic CO 2 concentration. At saturating CO 2 levels, the non-cyclic electron-transport rate, measured either as gross O 2 photosynthesis or as the chlorophyll fluorescence ratio (F m -F s)/F m, was insensitive to water deficit, provided RWD was below 40%. In this range of RWD, the decrease in gross O 2 photosynthesis observed in normal air was attributed to the inability of oxidative processes to sustain the maximal electron-flow rate at low chloroplastic CO 2 concentration. The maximal efficiency of photosystem II, estimated as the chlorophyll fluorescence ratio (F m -F 0)/F m measured in dark-adapted leaves, was not affected by water deficits up to 60%. 相似文献
16.
An open system associated with an infrared gas analyzer was employed to study transients in CO 2 exchange generated upon darkening preilluminated leaf discs of tobacco ( Nicotiana tabacum vars John Williams Broadleaf and Havana Seed). An empirical formula presented previously enabled prediction of the analyzer response under nonsteady state conditions as a function of time and of the leaf CO 2 exchange rate. A computer was used to evaluate parameters of the leaf CO 2 release rate to provide an estimate of the initial rate of postillumination CO 2 evolution and to produce maximal agreement between predicted and observed analyzer responses. In 21% O 2, the decline in rate of CO 2 evolution upon darkening followed first order kinetics. Initial rates of CO 2 evolution following darkening were relatively independent of the prior ambient CO 2 concentrations. However, rates of photorespiration expressed as a fraction of net photosynthesis declined rapidly with increasing external CO 2 concentration at 21% O 2. Under normal atmospheric conditions, photorespiration was 45 to 50% of the net CO 2 fixation rate at 32°C and high irradiance. The rapid initial CO 2 evolution observed upon darkening at 21% O 2 was absent in 3% O 2. Rates of photorespiration under normal atmospheric concentrations of CO 2 and O 2 as measured by the postillumination burst were highly dependent upon temperature (observed activation energy = 30.1 kilocalories per mole). The results are discussed with respect to previously published estimates of photorespiration in C 3 leaf tissue. 相似文献
17.
There is considerable variation among species in their rate of photorespiration, and photorespiration increases greatly at higher temperatures. The addition of an inhibitor of glycolate oxidase, α-hydroxy-2-pyridinemethanesulfonic acid, to tobacco leaf disks at 35° stimulated photosynthetic 14CO 2 uptake at least 3-fold, but 14CO 2 uptake was not changed by the inhibitor at 25°. The inhibitor did not increase photosynthesis in maize leaf disks at either temperature. 相似文献
18.
We classify mathematical models that can be used to describe photosynthetic oscillations using ideas from nonlinear dynamics, and discuss potential mechanisms for photosynthetic oscillations in the context of this classification. We then turn our attention to recent experiments with leaves transferred to a low CO 2 atmosphere which revealed stochastic oscillations with a period of a few seconds. Rubisco is the enzyme that takes both CO 2 and O 2 as substrates correspondingly for photosynthetic assimilation and for photorespiration. Photosynthesis depletes CO 2 and produces O 2 while respiration and photorespiration work in the opposite direction, so the product of one process becomes the reactant of the other coupled process. We examine the possibility of oscillations of CO 2 and O 2 in the leaf in relation to photorespiration. We suggest that in the cell, oscillations with a period of a few seconds, corresponding to the time between photosynthetic CO 2 fixation and photorespiratory CO 2 release, underlie the dynamics of metabolism in C 3 plants. 相似文献
19.
Primary leaves of bean ( Phaseolus vulgaris L.) seedlings cultivated for 14 days in a growth chamber on complete (control) and phosphate deficient (−P) Knop liquid medium
were used for measurements. The −P leaves were smaller and showed an increased specific leaf area (SLA). Their inorganic phosphate
(P i) concentration was considerably lowered. They did not show any significant changes in chlorophyll (Chl) ( a + b) concentration and in their net CO 2 assimilation rate when it was estimated under the conditions close to those of the seedlings growth. Light response curves
of photosynthetic net O 2 evolution ( P
NO 2) of the leaves for the irradiation range up to 500 μmol(photon) m −2 s −1 were determined, using the leaf-disc Clark oxygen electrode. The measurements were taken under high CO 2 concentration of about 1 % and O 2 concentrations of 21 % or lowered to about 3 % at the beginning of measurement. The results obtained at 21 % O 2 and the irradiations close to or higher than those used during the seedlings growth revealed the phosphorus stress suppressive
effect on the leaf net O 2 evolution, however, no such effect was observed at lower irradiations. Other estimated parameters of P
NO 2 such as: apparent quantum requirement (QR A) and light compensation point (LCP) for the control and −P leaves were similar. However, with a high irradiation and lowered
O 2 concentration the rate of P
NO 2 for the −P leaves was markedly higher than that for the control, in relation to both the leaf area and leaf fresh mass. This
difference also disappeared at low irradiations, but the estimated reduced QR A values indicate, under those conditions, the increased yield of photosynthetic light reaction, especially in the −P leaves.
The presented results confirm the suggestion that during the initial phase of insufficient phosphate feeding the acclimations
in the light phase of photosynthesis, both structural and functional appear. They correspond, probably, to the increased energy
costs of carbon assimilation under phosphorus stress, e.g. connected with raised difficulties in phosphate uptake and turnover and enhanced photorespiration. Under the experimental
conditions especially advantageous for the dark phase of photosynthesis (saturating CO 2 and PAR, low O 2 concentration), those acclimations may be manifested as an enhancement of photosynthetic net O 2 evolution. 相似文献
20.
A leaf disk assay for photorespiration has been developed based on the rate of release of recently fixed 14CO 2 in light in a rapid stream of CO 2-free air at 30° to 35°. In tobacco leaves (Havana Seed) photorespiration with this assay is 3 to 5 times greater than the 14CO 2 output in the dark. In maize, photorespiration is only 2% of that in tobacco. The importance of open leaf stomata, rapid flow rates of CO2-free air, elevated temperatures, and oxygen in the atmosphere in order to obtain release into the air of a larger portion of the 14CO2 evolved within the tissue in the light was established in tobacco. Photorespiration, but not dark respiration, was inhibited by α-hydroxy-2-pyridinemethanesulfonic acid, an inhibitor of glycolate oxidase, and by 3-(4-chlorophenyl)-1,1-dimethylurea (CMU), an inhibitor of photosynthetic electron transport, under conditions which did not affect the stomata. These experiments show that the substrates of photorespiration and dark respiration differ and also provide additional support for the role of glycolate as a major substrate of photorespiration. It was also shown that at 35° the quantity of 14CO2 released in the assay may represent only 33% of the gross 14CO2 evolved in the light, the remainder being recycled within the tissue. It was concluded that maize does not evolve appreciable quantities of CO2 in the light and that this largely accounts for the greater efficiency of net photosynthesis exhibited by maize. Hence low rates of photorespiration may be expected to be correlated with a high rate of CO2 uptake at the normal concentrations of CO2 found in air and at higher light intensities. 相似文献
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