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1.
The CO 2 and H 2O vapour exchange of single attached orange, Citrus sinensis (L.), leaves was measured under laboratory conditions using infrared gas analysis. Gaseous diffusive resistances were derived from measurements at a saturating irradiance and at a leaf temperature optimum for photosynthesis. Variation in leaf resistance (within the range 1.6 to 60 s cm -1) induced by moisture status, or by cyclic oscillations in stomatal aperture, was associated with changes in both photosynthesis and transpiration. At low leaf resistance (ri less than 10 s cm -1) the ratio of transpiration to photosynthesis declined with reduced stomatal aperture, indicating a tighter stomatal control over H 2O vapour loss than over CO 2 assimilation. At higher leaf resistance (ri greater than 10 s cm -1) changes in transpiration and photosynthesis were linearly related, but leaf resistance and mesophyll resistance were also positively correlated, so that strictly stomatal control of photosynthesis became more apparent than real. This evidence, combined with direct measurements of CO 2 diffusive resistances (in a -O 2 gas stream) emphasised the presence of a significant mesophyll resistance; i.e., an additional and rate limiting resistance to CO 2 assimilation over and above that encountered by H 2O vapour escaping from the leaf. 相似文献
2.
Transpiration was measured in apple leaves ( Malus sylvestris Mill.) which were enclosed in a leaf chamber and subjected to rapid changes in leaf temperature. Fluctuations in leaf temperature produced parallel fluctuations in transpiration. The change in transpiration rate with change in temperature was found to be less than the theoretical value calculated from the change in water vapour density gradient from leaf to air. The results suggest the presence of a small and rapidly varying resistance to water vapour loss from the leaf. The magnitude of this additional resistance increased to a maximum value of approximately 1.5 s cm -1 as the magnitude of the temperature change increased to a maximum of approximately 12°C. 相似文献
3.
Photosynthesis and transpiration of excised leaves of Taraxacum officinale L. and a few other species of plants were measured, using an open gas analysis system. The rates of CO 2 uptake and transpiration increased in two steps upon illumination of stomata-bearing epidermis of these leaves at a light intensity of 50 mW × cm −2. Abscisic acid inhibited only the second step of gas exchange. Illumination of the astomatous epidermis of hypostomatous leaves caused only the first step of gas exchange. These data indicate that the first and second steps arise from cuticular and stomatal gas exchange, respectively. The rate of the cuticular photosynthesis in a Taraxacum leaf reached saturation at a light intensity of 5 mW × cm −2, and the rates of the stomatal photosynthesis and transpiration reached saturation at a higher intensity of 35 mW × cm −2. The cuticular photosynthesis of a Taraxacum leaf was 18% of the stomatal photosynthesis at 50 mW × cm −2 and 270% at 5 mW × cm −2. The other species of leaves showed the same trend. The importance of cuticular CO 2 uptake in leaf photosynthesis, especially under low light intensity was stressed from these data. 相似文献
4.
Haberlea rhodopensis is a homoiochlorophyllous resurrection plant that shows a low rate of leaf net CO 2 uptake (4–6 μmol m ?2 s ?1) under saturating photosynthetic photon flux densities in air (21% O 2 and about 390 ppm CO 2). However, leaf net CO 2 uptake reaches values of 17–18 μmol m ?2 s ?1 under saturating CO 2 and light. H. rhodopensis leaves have a very low mesophyll CO 2 conductance that can partly explain the low rate of leaf net CO 2 uptake in normal air. Experimental evidences suggest that mesophyll conductance is not sensitive to temperature in the 20–35 °C range. In addition, it is shown that the (1) transpiration rate of H. rhodopensis is nearly linearly related to the vapour pressure difference between the leaf and the ambient air within the interval from 0.5 kPa to 2.5 kPa at a leaf temperature of 25 °C and (2) leaf net CO 2 uptake in normal air under saturating light does not change much with leaf temperature (between 20 °C and 30 °C). At a leaf relative water content of between 90% and 30%, the decrease of leaf net CO 2 assimilation during drought can be explained by a decrease of leaf CO 2 diffusional conductance. Accordingly the non-photochemical chlorophyll fluorescence quenching decreases only at relative water contents lower than 20%, indicating that photosynthetic activity maintains a trans-thylakoidal proton gradient over a wide range of leaf water contents. Moreover, PSII photochemistry (as estimated by the Fv/Fm ratio and the thermoluminescence B band intensity) is only affected at leaf relative water contents lower than about 20%, thus confirming that primary photosynthetic reactions are resistant to drought. Interestingly, the effect of leaf desiccation on photosynthetic capacity, measured at very high ambient CO 2 molar ratios under saturating PPFD, is identical to that observed for three non-resurrection C 3 mesophytes. This demonstrates that the photosynthetic apparatus of H. rhodopensis is not more resistant to desiccation when compared to other C 3 plants. Since the leaf area decreases by more than 50% when the leaf relative water content is reduced to about 40% during drought it is supposed, following Farrant et al. [Farrant, J.M., Vander, W.C., Lofell, D.A., Bartsch, S., Whittaker, A., 2003. An investigation into the role of light during desiccation of three angiosperms resurrection plants. Plant Cell Environ. 26, 1275–1286], that H. rhodopensis leaf cells avoid mechanical stress. 相似文献
5.
Global climate change may act as a potent agent of natural selection within species with Mediterranean mountain ecosystems being particularly vulnerable. The aim of this research was to analyze whether the phenotypic plasticity of Sesleria nitida Ten. could be indicative of its future adaptive capability to global warming. Morphological, anatomical, and physiological leaf traits of two populations of S. nitida growing at different altitudes on Mount Terminillo (Italy) were analyzed. The results showed that leaf mass per unit leaf area, leaf tissue density, and total leaf thickness were 19, 3, and 31% higher in leaves from the population growing at 1,895 m a.s.l. (B site) than in leaves from the population growing at 1,100 m a.s.l. (A site), respectively. Net photosynthetic rate ( P N) and respiration rate ( R D) peaked in June in both A and B leaves [9.4 ± 1.3 μmol(CO 2) m ?2 s ?1 and 2.9 ± 0.9 μmol(CO 2) m ?2 s ?1, respectively] when mean air temperature was 16 ± 2°C. R D/ P N was higher in B than in A leaves (0.35 ± 0.07 and 0.21 ± 0.03, respectively, mean of the study period). The mean plasticity index (PI = 0.24, mean of morphological, anatomical, and physiological leaf traits) reflected S. nitida adaptability to the environmental stress conditions at different altitudes on Mount Terminillo. Moreover, the leaf key traits of the two populations can be used to monitor wild populations over a long term in response to global change. 相似文献
6.
A new theory and experimental method was developed to measure the diffusion resistance to CO 2 in the gas phase of mesophyll leaf tissue. Excised leaves were placed in a chamber and their net evaporation and CO 2 assimilation rates measured at two different ambient pressures. These data were used to calculate CO 2 gas phase diffusion resistances. A variety of field grown leaves were tested and the effects of various experimental errors considered. Increasing the gas phase diffusion resistance decreased transpiration more than it decreased CO 2 assimilation. It was concluded that gas phase diffusion resistance associated with CO 2 assimilation may sometimes be 100 or 200 s·m -1 greater than the resistance implied by transpiration rates. This may be due to longer path lengths for the CO 2 diffusion, constricted in places by the shape and arrangement of mesophyll cells. 相似文献
7.
Photosynthesis and transpiration rates of transgenic (expressing yeast-derived invertase targeted to the vacuole) tobacco ( Nicotiana tabacum L.) leaves were, respectively, 50 and 70% of those of a wild type at 20°C, 350 cm 3 m ?3 CO 2 concentration, 450 μmol (photons) m ?2 s ?1 of light intensity, and 70% relative air humidity. These differences could be attributed: (a) to changes in leaf anatomy and, consequently, to changes in gases diffusion between the cells' surfaces and the atmosphere; (b) to different stomatal apertures, and, for the photosynthesis rate, (c) to the altered CO 2 assimilation rate. Our objective was to estimate the relative contributions of these three sources of difference. Measurements on the wild-type and the transgenic leaf cross-sections gave values for the cell area index (CAI, cell area surface per unit of leaf area surface) of 15.91 and 13.97, respectively. The two-dimensional model 2DLEAF for leaf gas exchange was used to estimate quantitatively anatomical, stomatal and biochemical components of these differences. Transpiration rate was equal to 0.9 for the wild-type and to 0.63 mmol m ?2 s ?1 for the transgenic leaf: 24.0% of the difference (0.066 mmol m ?2 s ?1 was caused by the greater cell area surface in the wild-type leaf, and 66.0% was caused by a smaller stomatal aperture in the transgenic leaf. Photosynthetic rate was 3.10 and 1.55 μmol m ?2 s ?1 for the wild-type and transgenic leaves, respectively. Only 10.3% of this difference (0.16 μmol m ?2 s ?1) was caused by the difference in CAI, and the remaining 89.7% was caused by altered CO 2 assimilation rate. 相似文献
8.
Hydrostatic pressures varying from 0 to 6.0 bar were applied to roots of intact Capsicum annuum L. cv. California Wonder plants growing in nutrient solution and the rates of transpiration, and net CO 2 assimilation, apparent compensation point and leaf water potential measured. Increasing the pressure on the roots of plants with roots in solution with either -0.5 or -5.0 bar osmotic potential with 1 bar increments resulted in a decrease in transpiration. With the application of 1 or 2 bar pressure the rate of transpiration returned to near or above the original rate. An application of 3 or 4 bar pressure reduced the rate of transpiration of all plants. The transpiration of plants with roots in solution with -0.5 bar osmotic potential remained at the reduced rate for as long as these pressures were maintained. The transpiration of plants with roots in solution with -5.0 bar was only temporarily suppressed at these pressures. Changing the applied pressure from 3 or 4 bar to 0 resulted in a rapid increase in transpiration which lasted approximately 15 minutes. This was followed by a decrease in transpiration to a rate lower than before the pressure was applied. The pattern of response was similar for plants at low or high light intensity or at normal or low CO 2 concentrations. When leaf diffusive resistance was 6.0 s cm ?1 or greater, changes in net CO 2 assimilation were similar to those of transpiration. The apparent CO 2 compensation point increased as pressure was applied and decreased with a release in pressure. Leaf water potential increased with an increase in pressure and decreased with a decrease in pressure. The changes in leaf water potential were frequently but not always proportional to changes in pressure. It is postulated that the respouses noted were due to changes in resistance to flow of water from xylem terminals through the mesophyll cells and stomatal cavities to the atmosphere. 相似文献
9.
A system for measurement of leaf gas exchange while regulating leaf to air vapour pressure difference has been developed; it comprises an assimilation chamber, leaf temperature controller, mass flow controller, dew point controller and personal computer. A relative humidity sensor and air and leaf temperature sensors, which are all used for regulating the vapour pressure difference, are mounted into the chamber. During the experiments, the computer continuously monitored the photosynthetic parameters and measurement conditions, so that accurate and intenstive measurements could be made.When measuring the light-response curve of CO 2 assimilation for single leaves, in order to regulate the vapour pressure difference, the leaf temperature and relative humidity in the chamber were separately and simultaneously controlled by changing the air temperature around the leaf and varying the air flow rate through the chamber, respectively. When the vapour pressure difference was regulated, net CO 2 assimilation, transpiration and leaf conductance for leaves of rice plant increased at high quantum flux density as compared with those values obtained when it was not regulated.When measuring the temperature-response curve of CO 2 assimilation, the regulation of vapour pressure difference was manipulated by the feed-forward control of the dew point temperature in the inlet air stream. As the vapour pressure difference was regulated at 12 mbar, the maximum rate of and the optimum temperature for CO 2 assimilation in rice leaves increased 5 molCO 2 m –2 s –1 and 5°C, respectively, as compared with those values obtained when the vapour pressure difference took its own course. This was reasoned to be due to the increase in leaf conductance and the decrease in transpiration rate. In addition, these results confirmed that stomatal conductance essentially increases with increasing leaf temperature under constant vapour pressure difference conditions, in other words, when the influence of the vapour pressure difference is removed.This system may be used successfully to measure inter- and intra-specific differences and characteristics of leaf gas exchange in plants with a high degree of accuracy.Abbreviations A
CO 2 assimilation rate
- A max
Maximum rate of CO 2 assimilation
- A opt
Optimum teperature for CO 2 assimilation
- CTWB
Controlled-temperature water bath
- DPC
Dew point controller
- E
Transpiration rate; gl, leaf conductance
- HCC
Humidity control circuit
- IRGA
Infrared gas analyzer
- LT
Leaf temperature
- LTC
Leaf temperature controller
- MFC
Mass flow controller
- QFD
Quantum flux density
- RH
Relative humidity
- RHC
Relative humidity controller
- VPD
Vapour pressure difference
- CO 2
Difference of CO 2 concentration between inlet and outlet air 相似文献
10.
The increase in the measured transpiration rate in tobacco leaves due to the experimentally decreased humidity of the bulk air was found to be significantly lower than the theoretical value calculated from the change of water vapour concentration gradients. Boundary layer and stomatal diffusive resistances remained unchanged under experimental conditions with no change of net photosynthetic CO 2 uptake. This suggests an increase in intercellular diffusive resistance with an increase in water vapour concentration gradient which is the driving force of water vapour diffusive part of transpiration flux. The increase can be ascribed to the lengthening of intercellular diffusive pathway as steeper water vapour concentration gradient in intercellular spaces results in an increased evaporating surface of intercellular cells thus moving the effective plane of vaporization in leaf mesophyll further inwards. Due to different and independent changes of concentration gradients for water vapour and CO 2, different length of intercellular diffusive pathways for CO 2 and water vapour may be expected. 相似文献
11.
CO 2 exchange, transpiration and leaf water potential of Welwitschia mirabilis were measured in three contrasting habitats of the Namib desert. From these measurements stomatal conductance, internal CO 2concentration and WUE were calculated. In two of the three habitats photosynthetic CO 2 uptake decreased and transpiration increased with increasing leaf age while in the third habitat CO 2 uptake increased and transpiration decreased with leaf age. Except for the stomata of young leaf sections in this habitat, stomata closed with increasing δw leading to a pronounced midday depression of CO 2 uptake. The high stomatal limitation of photosynthetic CO 2 uptake of glasshouse-grown plants was verified in the natural habitat. Photosynthetic CO 2 uptake saturated between 800 and 1300 μmol photons m ?2 s ?1depending on leaf age and habitat. CO 2 uptake had a broad temperature optimum declining significantly beyond 32 °C. Predawn leaf water potential reflected water availability and atmospheric conditions in the three habitats and ranged from ? 2.5 to ? 6.2 MPa. There was a pronounced diurnal course of leaf water potential in all habitats. During the day a gradient in water potential developed along the leaf axis with the lowest potential at the leaf's tip. With respect to whole plant balances of CO 2 exchange and transpiration, there were marked differences between Welwitschias in the three habitats. Despite a negative CO 2 balance over a period of five months, leaves in the driest habitat grew constantly at the expense of carbon reserves in the plant. Only at the wettest site did carbon gain exceed carbon demand for growth. The WUE of whole plants was insignificant in all habitats. The results were as contrasting as the habitats and plants and did not allow generalisations about adaptational features of Welwitschia mirabilis. 相似文献
12.
The influences of illumination, temperature, and soil water potential during development on leaf thickness, mesophyll cell wall area per unit leaf area ( Ames/A), and the cellular CO 2, resistance expressed on a mesophyll cell wall area basis ( rCO2cell,) were examined for Plectranthus parviflorus Henckel. Although the ranges of all three growth conditions caused at least 9-fold variations in the leaf biomass produced in 4 weeks, only the illumination had a major effect on internal leaf morphology, e.g. the thickness went from 279 to 831 μm and Ames/ A from 10.5 to 34.8 as the photosynthetically active radiation was raised from 3 to 53 nEinsteins cm ?2 s ?1, while rCO2cell remained close to 154 s cm ?1. Variations in the growth temperature, soil water potential, and the nutritional status of the plant, affected photosynthesis mainly by changes in rCO2cell. To compare the influence of internal leaf area on photosynthesis for other plants, especially those with low Ames/ A values, the maximum rates of CO 2 uptake at light saturation and photosynthetically optimal temperatures were also determined for a moss, Mnium ciliare (C. Muell.) Schimp., and two ferns, Adiantum decorum Moore and Alsophila australe R. Br. As Ames/ A went from 2.00 for the moss to 3.8, 7.5, 11.7, and 20.8 for the fens, the illumination at light saturation and the maximum rate of photosynthesis both progressively increased. The cellular CO 2 resistance, which theoretically might have a lower limit of 20 s cm ?1, ranged from 85 to 190 s cm ?1. 相似文献
13.
Stepwise increases in fluorescent illuminance, imposed as a single variable in a controlled environment, induced progressive stomatal opening in 8 plant species, as evidenced by a consistent decrease in leaf diffusion resistance (R L), ranging from 15 to 70 sec cm −1 in darkness to about 1 sec cm −1 at approximately 40 kilolux. The minimum R L values were the same for the upper and the lower epidermis, provided that stomatal density was adequate. Saturation illuminance was not achieved in any species; extrapolation indicates that 50 kilolux would bring about full stomatal opening (R L ≤ 0.1 sec cm −1). In 4 species, reasonable agreement was obtained in a controlled environment between transpiration as measured by weight loss and that calculated from determination of (a) the difference in water vapor density from leaf to air, (b) the boundary layer resistance, and (c) the leaf diffusion resistance. This result confirms the physical validity of the resistance measurement procedure. 相似文献
14.
The factors responsible for the low transpiration rates of citrus were investigated. Leaf resistance to water vapor exchange by orange seedlings ( Citrus sinensis L. cv. Koethen) including a substantial boundary layer resistance, was as low as 1 s cm −1 in humid air. Leaf resistance of well watered plants increased to values as large as 5 s cm −1 when the difference in absolute humidity between leaf and air was increased. Leaf resistance was only slightly influenced by temperature between 20 and 30°C providing the humidity difference between leaf and air was kept constant. Leaf resistance increased when leaf temperature was increased between 20 and 30°C when the absolute humidity external to the leaf was kept constant. Increased humidity differences resulted in greater increases in leaf resistance during initial experiments than when the experiments were repeated with the same leaves indicating acclimation by the plant. It was concluded that the effects of humidity differences on leaf resistance are partially responsible for the low transpiration rates of citrus. 相似文献
15.
Abstract. Cuticular resistance to water vapour diffusion is an important aspect of thermocouple psychrometry and may introduce significant error in the measurement of leaf water potential (Ψ). The effect of the citrus ( Citrus mitis Blanco) leaf cuticle on water vapour movement was studied using the times required for vapour pressure equilibration during thermocouple psychrometric measurement of Ψ. Cuticular abrasion with various carborundum powders was used to reduce the diffusive resistance of both the adaxial and abaxial leaf surfaces, and the extent of the disruption to the leaf was investigated with light and electron microscopy. Cuticular abrasion resulted in reduced equilibration times due to decreased cuticular resistance and greater water vapour movement between the leaf and the psychrometer chamber. Equilibration times were reduced from over 5 h in the unabraded control leaves to 1 h with cuticle abrasion. This was associated with the decrease in diffusive resistance with cuticular abrasion from over 55 s cm ?1 to less than 8 s cm ?1 for both the adaxial and abaxial leaf surfaces. Scanning electron micrographs of the abraded leaf tissue revealed considerable disruption of the stomatal ledge and of the guard cells, surface smoothing and displacement of waxes into the stomatal aperture, and damage to veins. Observations with the transmission electron microscope revealed frequent disruption of epidermal cell walls, and damage to both the cytoplasmic and vacuolar membranes. 相似文献
16.
This study investigates effects of climate warming (+ 2.5°C ubove ambient) and elevated CO 2 concentration (600 μmol mol ?1) on the stomatal functioning and the water relations of Lolium perenne, using Free Air Temperature Increase (FATI) and Free Air CO 2 Enrichment (FACE). Compared to growth at ambient temperature, whole-season temperature increase reduced leaf stomatal conductance, but only at the top of the canopy (-14.6 and -8.8% at ambient and elevated CO 2, respectively). However, because higher canopy temperature raised the leaf-to-air vapour pressure difference, leaf transpiration rate increased (+28% at ambient and +48% at elevated CO 2) and instantaneous leaf water use efficiency, derived from short-term measurements of assimilation and transpiration rate, declined (-11% at ambient and -13% at elevated CO 2). Nevertheless, at the stand level, growth at + 2.5°C reduced transpiration due to fewer tillers per plant and a smaller leaf area per tiller. This sparser vegetation was also more closely coupled to the atmosphere and maintained a drier internal microclimate. To assess whether the stomatal behaviour observed in this experiment could be explained by prevailing concepts of stomatal functioning, three models were applied (Cowan 1977; Ball, Woodrow & Berry 1987; Leuning 1995). The latter model accounted for the highest proportion of variability in the data (58%) and was insensitive to CO 2 and temperature regime, which suggests that the principles of stomatal regulation are not affected by changes in CO 2 or climate. 相似文献
17.
In upland cotton ( Gossypium hirsutum L.) certain varieties are available with the mutant character “okra” leaves. These deeply lobed leaves were found to have thinner boundary layers than their normal analogues. Apparent photosynthesis and transpiration measurements were made in field-grown stands under a variety of light intensities and carbon dioxide levels to assess the effect of leaf boundary layer diffusion resistance on photosynthetic efficiency. The thinner boundary layers associated with deeply lobed “okra” cotton failed to euhance carbon fixation rates per unit land area. It was concluded that the leaf boundary layer resistance under field conditions is small compared with the total CO 2 diffusion resistance. 相似文献
18.
Abstract Photosynthetic responses to light, temperature and leaf-to-air water vapour concentration deficit for Strophostyles helvola (L.) Ell. in an open beach site, and Amphicarpa bracteata (L.) Ell. in two deciduous forest sites were quantified. Photosaturated rates of net CO 2 assimilation were 52.1 ± 4.6, 11.0 ± 1.6 and 4.1 ± 0.3 μmol m ?2s ?2 for plants in beach, roadside and closed canopy sites, respectively. In terms of photosynthesis, plants in the beach site were more tolerant of higher leaf temperatures and water vapour concentration deficits than were plants in forested sites. Heliotropic leaf movements in the beach site reduced calculated total daily transpiration by 2%, increased total daily carbon gain by 8% and reduced the transpiration ratio by 9% relative to an horizontal leaf. During long-term sunflecks in forested sites, heliotropism reduced transpiration by 15%, increased carbon gain by 71% and reduced the transpiration ratio by 50% relative to an horizontal leaf. We hypothesize that heliotropic leaf movements in mesic, high-light, low-nitrogen habitats may increase carbon return on nitrogen investment in photosynthesis, while heliotropism in canopy gaps may represent a morphological mechanism to reduce damage to low-light acclimated photosynthetic systems during long-term sunflecks. 相似文献
19.
At several heights and times of day within a crop of Zea mays, internal leaf diffusion resistance ( ri) and external boundary layer diffusion resistance ( ra) were evaluated by measuring the temperature of a transpiring and a non-transpiring leaf (simulated by covering both sides of a normal leaf with strips of poly-ethylene tape), and by measuring the immediate air temperature, humidity and windspeed. Both ra and ri increased with depth into the crop. However, ra generally was less than 10% of ri. Profiles of latent-heat flux density and source intensity of transpiration showed that transpiration corresponded roughly to foliage distribution (with an upward shift) and were not similar to the profile of radiation absorption. The data were compared with heat budget data. The 2 approaches yielded quite similar height distributions of transpiration per unit leaf area and total transpiration resistance. The total crop resistance to transpiration was computed as 0.027 min cm−1. This compares to Monteith's values of 0.017 to 0.040 min cm−1 for beans (Phaseolus vulgaris L.), and Linacre's values of 0.015 to 0.020 min cm−1 for turf. 相似文献
20.
Summary The lower epidermis from leaves of Primula palinuri can be stripped off. Light-saturation curves of the CO 2-exchange were measured at 20°C and 300 ppm CO 2. Whereas the normal leaf reaches light-saturation at 0.3 cal cm -2 min -1, even 0.6 cal cm -2 min -1 is not sufficient to saturate the stripped leaf. Transpiration, apparent CO 2-uptake and leaf-temperature were measured simultaneously. The data were used to calculate the diffusion resistances for CO 2 with the usual methods, that is, from the diffusion resistances for water-vapour transport. The comparison of the CO 2-exchange of stripped and normal leaves makes it possible to determine the resistances—in particular those of the stomata—directly from the CO 2-exchange. Both methods agree well. When CO 2 exchanges only through the lower surface of the leaf the epidermis is—even with opened stomata—a considerable diffusion resistance. It lowers the CO 2-concentration in the intercellular system to 160 ppm and limits the CO 2-uptake. 相似文献
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