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1.
Carbon exchange capacity of cucumber ( Cucumis sativus L.) germinated and grown in controlled environment chambers at 1000 microliters per liter CO 2 decreased from the vegetative growth stage to the fruiting stage, during which time capacity of plants grown at 350 microliters per liter increased. Carbon exchange rates (CERs) measured under growth conditions during the fruiting period were, in fact, lower in plants grown at 1000 microliters per liter CO 2 than those grown at 350. Progressive decreases in CERs in 1000 microliters per liter plants were associated with decreasing stomatal conductances and activities of ribulose bisphosphate carboxylase and carbonic anhydrase. Leaf starch concentrations were higher in 1000 microliters per liter CO 2 grown-plants than in 350 microliters per liter grown plants but calcium and nitrogen concentrations were lower, the greatest difference occurring at flowering. Sucrose synthase and sucrose-P-synthase activities were similar in 1000 microliters per liter compared to 350 microliters per liter plants during vegetative growth and flowering but higher in 350 microliters per liter plants at fruiting. The decreased carbon exchange rates observed in this cultivar at 1000 microliters per liter CO 2 could explain the lack of any yield increase (MM Peet 1986 Plant Physiol 80: 59-62) when compared with plants grown at 350 microliters per liter. 相似文献
2.
Leaf gas exchange characteristics of a desert annual ( Triticum kotschyi [Boiss.] Bowden) and the wheat cultivar TAM W-101 ( Triticum aestivum L. em Thell) were compared over a range of leaf water potentials from −0.50 to −2.9 megapascals. At an ambient [CO 2] of 330 microliters per liter, T. kotschyi had higher conductance and CO 2 assimilation (A) at a given water potential than T. aestivum. Under well watered conditions, A versus internal CO 2 concentration (C i) response curves for both species were similar in shape and magnitude, and the higher A of T. kotschyi at an ambient [CO 2] of 330 microliters per liter was mostly related to the higher stomatal conductance of T. kotschyi. The higher conductance of T. kotschyi than T. aestivum under well watered conditions was associated with higher C i and lower water use efficiency. Under water deficits, however, C i at 330 microliters per liter ambient [CO 2] did not differ significantly between species. T. kotschyi had higher A under water deficits than T. aestivum primarily because its A versus C i response curves had higher A at C i values above about 150 microliters per liter. The results show that conductance played an important role in the high A of T. kotschyi under well watered conditions, but under water deficits the high A of T. kotschyi was related more to the maintenance of a higher capacity for mesophyll photosynthesis. 相似文献
3.
The inhibition of photosynthesis at low leaf water potentials was studied in soil-grown sunflower to determine the degree to which photosynthesis under high light was affected by stomatal and nonstomatal factors. Below leaf water potentials of −11 to −12 bars, rates of photosynthesis at high light intensities were insensitive to external concentrations of CO 2 between 200 and 400 microliters per liter. Photosynthesis also was largely insensitive to leaf temperature between 10 and 30 C. Changes in CO 2 concentration and temperature had negligible effect on leaf diffusive resistance. The lack of CO 2 and temperature response for both photosynthesis and leaf diffuse resistance indicates that rates of photosynthesis were not limited by either CO 2 diffusion or a photosynthetic enzyme. It was concluded that photosynthesis under high light was probably limited by reduced photochemical activity of the leaves at water potentials below −11 to −12 bars. 相似文献
4.
We investigated the possibility of interspecific water transfer in an alfalfa ( Medicago sativa L.) and maize ( Zea mays L.) association. An alfalfa plant was grown through two vertically stacked plastic tubes. A 5 centimeter air gap between tubes was bridged by alfalfa roots. Five-week old maize plants with roots confined to the top tube were not watered, while associated alfalfa roots had free access to water in the bottom tube (the −/+ treatment). Additional treatments included: top and bottom tubes watered (+/+), top and bottom tubes droughted (−/−), and top tube droughted after removal of alfalfa root bridges and routine removal of alfalfa tillers (− *). Predawn leaf water potential of maize in the −/+ treatment fell to −1.5 megapascals 13 days after the start of drought; thereafter, predawn and midday potentials were maintained near −1.9 megapascals. Leaf water potentials of maize in the −/− and − * treatments declined steadily; all plants in these treatments were completely desiccated before day 50. High levels of tritium activity were detected in water extracted from both alfalfa and maize leaves after 3H 2O was injected into the bottom −/+ tube at day 70 or later. Maize in the −/+ treatment was able to survive an otherwise lethal period of drought by utilizing water lost by alfalfa roots. 相似文献
5.
The extent and occurrence of water stress-induced “patchy” CO 2 uptake across the surface of leaves was evaluated in a number of plant species. Leaves, while still attached to a plant, were illuminated and exposed to air containing [ 14C]CO 2 before autoradiographs were developed. Plant water deficits that caused leaf water potential depression to −1.1 megapascals during a 4-day period did result in heterogenous CO 2 assimilation patterns in bean ( Phaseolus vulgaris). However, when the same level of stress was imposed more gradually (during 17 days), no patchy stomatal closure was evident. The patchy CO 2 assimilation pattern that occurs when bean plants are subjected to a rapidly imposed stress could induce artifacts in gas exchange studies such that an effect of stress on chloroplast metabolism is incorrectly deduced. This problem was characterized by examining the relationship between photosynthesis and internal [CO 2] in stressed bean leaves. When extent of heterogenous CO 2 uptake was estimated and accounted for, there appeared to be little difference in this relationship between control and stressed leaves. Subjecting spinach ( Spinacea oleracea) plants to stress (leaf water potential depression to −1.5 megapascals) did not appear to cause patchy stomatal closure. Wheat ( Triticum aestivum) plants also showed homogenous CO 2 assimilation patterns when stressed to a leaf water potential of −2.6 megapascals. It was concluded that water stress-induced patchy stomatal closure can occur to an extent that could influence the analysis of gas exchange studies. However, this phenomenon was not found to be a general response. Not all stress regimens will induce patchiness; nor will all plant species demonstrate this response to water deficits. 相似文献
6.
As sugar beet source leaves lowered the CO 2 concentration to compensation point in a closed atmosphere, leaf thickness and relative water content decreased. Leaf water potential declined rapidly from −0.5 to −1.4 megapascals. At 340 microliters CO 2 per liter, water potential and sucrose, glucose, and fructose contents were steady in photosynthesizing source leaves. Within 90 minutes after leaves were exposed to a CO 2 concentration at the compensation point, leaf sucrose content declined to 60% of the preteatment level, rapidly in the first 30 minutes and then more slowly. During the subsequent 200 minutes, sucrose content increased to 180% of pretreatment level. Glucose and fructose remained unchanged during the treatment. Degradation of starch was sufficient to account for the additional sucrose that accumulated. Labeled carbon lost from starch appeared in sucrose and several other compounds that likely contributed to the recovery in leaf water content. 相似文献
7.
Plants of Sedum rubrotinctum R. T. Clausen were studied in a green-house over a 2-year period without watering. Only the apical leaves survived and were turgid at the end of the experiment. The midday leaf water potential of these apical leaves was −1.20 megapascals, while the leaf water potential of comparable leaves on well-watered control plants was −0.20 megapascals. The unwatered plants appear to have maintained turgor by means of an osmotic adjustment. After 2 years without water the plants no longer exhibited a nocturnal accumulation of titratable acidity. However, the daytime levels of titratable acidity of the unwatered plants were more than 2-fold greater than the levels in well-watered control plants. Well-watered plants of S. rubrotinctum exhibited seasonal shifts in biomass stble carbon isotope ratios, indicating a greater proportion of day versus night CO 2 uptake in the winter than in the summer. The imposition of water stress prevented the expression of this seasonal rhythm and restricted the plants to dark CO 2 uptake. 相似文献
8.
The short term effects of increased levels of CO 2 on gas exchange of leaves of bigtooth aspen ( Populus grandidentata Michx.) were studied at the University of Michigan Biological Station, Pellston, MI. Leaf gas exchange was measured in situ in the upper half of the canopy, 12 to 14 meters above ground. In 1900 microliters per liter CO 2, maximum CO 2 exchange rate (CER) in saturating light was increased by 151% relative to CER in 320 microliters per liter CO 2. The temperature optimum for CER shifted from 25°C in 320 microliters per liter CO 2 to 37°C in 1900 microliters per liter CO 2. In saturating light, increasing CO 2 level over the range 60 to 1900 microliters per liter increased CER, decreased stomatal conductance, and increased leaf water use efficiency. The initial slope of the CO 2 response curve of CER was not significantly different at 20 and 30°C leaf temperatures, although the slope did decline significantly during leaf senescence. In 1900 microliters per liter CO 2, CER increased with increasing light. The light saturation point and maximum CER were higher in 30°C than in 20°C, although there was little effect of temperature in low light. The experimental results are consistent with patterns seen in laboratory studies of other C 3 species and define the parameters required by some models of aspen CER in the field. 相似文献
9.
Photosynthetic CO 2 assimilation, transpiration, ribulose-1,5-bisphosphate carboxylase (RuBPCase), and soluble protein were reduced in leaves of water-deficit (stress) `Valencia' orange ( Citrus sinensis [L.] Osbeck). Maximum photosynthetic CO 2 assimilation and transpiration, which occurred before midday for both control and stressed plants, was 58 and 40%, respectively, for the stress (−2.0 megapascals leaf water potential) as compared to the control (−0.6 megapascals leaf water potential). As water deficit became more severe in the afternoon, with water potential of −3.1 megapascals for the stressed leaves vs. −1.1 megapascals for control leaves, stressed-leaf transpiration declined and photosynthetic CO 2 assimilation rapidly dropped to zero. Water deficit decreased both activation and total activity of RuBPCase. Activation of the enzyme was about 62% (of fully activated enzyme in vitro) for the stress, compared to 80% for the control. Water deficit reduced RuBPCase initial activity by 40% and HCO 3−/Mg 2+-saturated activity by 22%. However, RuBPCase for both stressed and control leaves were similar in Kcat (25 moles CO 2 per mole enzyme per second) and Km for CO 2 (18.9 micromolar). Concentrations of RuBPCase and soluble protein of stressed leaves averaged 80 and 85%, respectively, of control leaves. Thus, reductions in activation and concentration of RuBPCase in Valencia orange leaves contributed to reductions in enzyme activities during water-deficit periods. Declines in leaf photosynthesis, soluble protein, and RuBPCase activation and concentration due to water deficit were, however, recoverable at 5 days after rewatering. 相似文献
10.
Growth at an elevated CO 2 concentration resulted in an enhanced capacity for soybean ( Glycine max L. Merr. cv Bragg) leaflet photosynthesis. Plants were grown from seed in outdoor controlled-environment chambers under natural solar irradiance. Photosynthetic rates, measured during the seed filling stage, were up to 150% greater with leaflets grown at 660 compared to 330 microliters of CO 2 per liter when measured across a range of intercellular CO 2 concentrations and irradiance. Soybean plants grown at elevated CO 2 concentrations had heavier pod weights per plant, 44% heavier with 660 compared to 330 microliters of CO 2 per liter grown plants, and also greater specific leaf weights. Ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco) activity showed no response (mean activity of 96 micromoles of CO 2 per square meter per second expressed on a leaflet area basis) to short-term (~1 hour) exposures to a range of CO 2 concentrations (110-880 microliters per liter), nor was a response of activity (mean activity of 1.01 micromoles of CO 2 per minute per milligram of protein) to growth CO 2 concentration (160-990 microliters per liter) observed. The amount of rubisco protein was constant, as growth CO 2 concentration was varied, and averaged 55% of the total leaflet soluble protein. Although CO 2 is required for activation of rubisco, results indicated that within the range of CO 2 concentrations used (110-990 microliters per liter), rubisco activity in soybean leaflets, in the light, was not regulated by CO 2. 相似文献
11.
Needles from phosphorus deficient seedlings of Pinus radiata D. Don grown for 8 weeks at either 330 or 660 microliters CO 2 per liter displayed chlorophyll a fluorescence induction kinetics characteristic of structural changes within the thylakoid chloroplast membrane, i.e. constant yield fluorescence (F O) was increased and induced fluorescence ([F P-F I]/F O) was reduced. The effect was greatest in the undroughted plants grown at 660 μl CO 2 L −1. By week 22 at 330 μl CO 2 L −1 acclimation to P deficiency had occurred as shown by the similarity in the fluorescence characteristics and maximum rates of photosynthesis of the needles from the two P treatments. However, acclimation did not occur in the plants grown at 660 μl CO 2 L −1. The light saturated rate of photosynthesis of needles with adequate P was higher at 660 μl CO 2 L −1 than at 330 μl CO 2 L −1, whereas photosynthesis of P deficient plants showed no increase when grown at the higher CO 2 concentration. The average growth increase due to CO 2 enrichment was 14% in P deficient plants and 32% when P was adequate. In drought stressed plants grown at 330 μl CO 2 L −1, there was a reduction in the maximal rate of quenching of fluorescence (R Q) after the major peak. Constant yield fluorescence was unaffected but induced fluorescence was lower. These results indicate that electron flow subsequent to photosystem II was affected by drought stress. At 660 μl CO 2 L −1 this response was eliminated showing that CO 2 enrichment improved the ability of the seedlings to acclimate to drought stress. The average growth increase with CO 2 enrichment was 37% in drought stressed plants and 19% in unstressed plants. 相似文献
12.
The effects of water stress and CO 2 enrichment on photosynthesis, assimilate export, and sucrose-P synthase activity were examined in field grown soybean plants. In general, leaves of plants grown in CO 2-enriched atmospheres (300 microliters per liter above unenriched control, which was 349 ± 12 microliters per liter between 0500 and 1900 hours EST over the entire season) had higher carbon exchange rates (CER) compared to plants grown at ambient CO 2, but similar rates of export and similar activities of sucrose-P synthase. On most sample dates, essentially all of the extra carbon fixed as a result of CO 2 enrichment was partitioned into starch. CO 2-enriched plants had lower transpiration rates and therefore had a higher water use efficiency (milligrams CO 2 fixed per gram H 2O transpired) per unit leaf area compared to nonenriched plants. Water stress reduced CER in nonenriched plants to a greater extent than in CO 2-enriched plants. As CER declined, stomatal resistance increased, but this was not the primary cause of the decrease in assimilation because internal CO 2 concentration remained relatively constant. Export of assimilates was less affected by water stress than was CER. When CERs were low as a result of the imposed stress, export was supported by mobilization of reserves (mainly starch). Export rate and leaf sucrose concentration were related in a curvilinear manner. When sucrose concentration was above about 12 milligrams per square decimeter, obtained with nonstressed plants at high CO 2, there was no significant increase in export rate. Assimilate export rate was also correlated positively with SPS activity and the quantitative relationship varied with CER. Thus, export rate was a function of both CER and carbon partitioning. 相似文献
13.
Soybean ( Glycine max L. Merrill cv `Bragg') plants were grown in pots at six elevated atmospheric CO 2 concentrations and two watering regimes in open top field chambers to characterize leaf xylem potential, stomatal resistance and conductance, transpiration, and carbohydrate contents of the leaves in response to CO 2 enrichment and water stress conditions. Groups of plants at each CO 2 concentration were subjected to water stress by withholding irrigation for 4 days during the pod-filling stage. Under well watered conditions, the stomatal conductance of the plants decreased with increasing CO2 concentration. Therefore, although leaf area per plant was greater in the high CO2 treatments, the rate of water loss per plant decreased with CO2 enrichment. After 4 days without irrigation, plants in lower CO2 treatments showed greater leaf tissue damage, lower leaf water potential, and higher stomatal resistance than high CO2 plants. Stomatal closure occurred at lower leaf water potentials for the low CO2 grown plants than the high CO2 grown plants. Significantly greater starch concentrations were found in leaves of high CO2 plants, and the reductions in leaf starch and increases in soluble sugars due to water stress were greater for low CO2 plants. The results showed that even though greater growth was observed at high atmospheric CO2 concentrations, lower rates of water use delayed and, thereby, prevented the onset of severe water stress under conditions of low moisture availability. 相似文献
14.
Greenhouse-grown pigeonpea ( Cajanus cajan, [L.] Millsp.; cultivar UW-10) and cowpea ( Vigna unguiculata, [L.] Walp.; cultivar California No. 5) were well-watered (control) or subjected to low water potential by withholding water to compare their modes of adaptation to water-limited conditions. Leaf CO 2 exchange rate (CER), leaf diffusive conductance to CO 2 ( gl), and CO 2 concentration in the leaf intercellular air space (C i) were determined at various CO 2 concentrations and photon flux densities (PFD) of photosynthetically active radiation (400 to 700 nanometer). In cowpea, gl declined to less than 15% of controls and total water potential (ψ w) at midafternoon declined to −0.8 megapascal after 5 days of withholding water, whereas gl in pigeonpea was about 40% of controls even though midafternoon ψ w was −1.9 megapascal. After 8 days of withholding water, ψ w at midafternoon declined to −0.9 and −2.4 megapascals in cowpea and pigeonpea, respectively. The solute component of water potential (ψ s) decreased substantially less in cowpea than pigeonpea. Photosynthetic CER at saturation photon flux density (PFD) and ambient external CO 2 concentration (360 microliters per liter) on day 5 of withholding decreased by 83 and 55% in cowpea and pigeonpea, respectively. When measured at external, CO 2 concentration in bulk air of 360 microliters per liter, the CER of cowpea had fully recovered to control levels 3 days after rewatering; however, at 970 microliters per liter the PFD-saturated CERs of both species were substantially lower than in controls, indicating residual impairment. In stressed plants of both species the CER responses to C i from 250 to 600 microliters per liter indicated that a substantial nonstomatal inhibition of CER had occurred. Although the sensitivity of gl to water limitation in cowpea suggested a dehydration avoidance response, parallel measurements of CER at various C i and PFD indicated that photosynthetic activity of cowpea mesophyll was substantially inhibited by the water-limited treatment. 相似文献
15.
Soybean [ Glycine max (L.) Merr. cv. Williams 82 and A3127] plants were grown in the field under long-term soil moisture deficit and irrigation to determine the effects of severe drought stress on the photosynthetic capacity of soybean leaves. Afternoon leaf water potentials, stomatal conductances, intercellular CO 2 concentrations and CO 2-assimilation rates for the two soil moisture treatments were compared during the pod elongation and seed enlargement stages of crop development. Leaf CO 2-assimilation rates were measured with either ambient (340 l CO 2 l –1) or CO 2-enriched (1800 l CO 2 l –1) air. Although seed yield and leaf area per plant were decreased an average of 48 and 31%, respectively, as a result of drought stress, leaf water potentials were reduced only an average of 0.27 MPa during the sampling period. Afternoon leaf CO 2-assimilation rates measured with ambient air were decreased an average of 56 and 49% by soil moisture deficit for Williams 82 and A3127, respectively. The reductions in leaf photosynthesis of both cultivars were associated with similar decreases in leaf stomatal conductance and with small increases in leaf intercellular CO 2 concentration. When the CO 2-enriched air was used, similar afternoon leaf CO 2-assimilation rates were found between the soil moisture treatments at each stage of crop development. These results suggest that photosynthetic capacity of soybean leaves is not reduced by severe soil moisture deficit when a stress develops gradually under field conditions.Abbreviations C i
intercellular CO 2 concentrations
- A a
rates of CO 2 assimilation measured with ambient air
- A e
rates of CO 2 assimilation measured with CO 2-enriched air
- g s
stomatal conductances
- RuBPCase
ribulose-1,5-bisphosphate carboxylase 相似文献
16.
For the leaf succulent Agave deserti and the stem succulent Ferocactus acanthodes, increasing the ambient CO 2 level from 350 microliters per liter to 650 microliters per liter immediately increased daytime net CO 2 uptake about 30% while leaving nighttime net CO 2 uptake of these Crassulacean acid metabolism (CAM) plants approximately unchanged. A similar enhancement of about 30% was found in dry weight gain over 1 year when the plants were grown at 650 microliters CO 2 per liter compared with 350 microliters per liter. Based on these results plus those at 500 microliters per liter, net CO 2 uptake over 24-hour periods and dry weight productivity of these two CAM succulents is predicted to increase an average of about 1% for each 10 microliters per liter rise in ambient CO 2 level up to 650 microliters per liter. 相似文献
17.
The physiological and physical components of the feedback loop involving intercellular CO 2 concentration (c i) and stomata are identified. The loop gain (G) is a measure of the degree of homeostasis in a negative feedback loop [the expression 1/(1-G) represents the fraction to which feedback reduces a perturbance]. Estimates are given for the effects of G on responses of stomata and c i to changes in ambient CO 2 concentration, light intensity, and perturbations in the water relations of a leaf. At normal ambient CO 2 concentration, the gain of the loop involving stomatal conductance and c i was found to be −2.2 in field-grown Zea mays, −3.6 if plants of this species were grown in a growth chamber, and zero in well watered Xanthium strumarium in the vegetative state. 相似文献
18.
Mild water stress, on the order of −1.0 megapascals xylem water potential, can reduce the rate of photosynthesis and eliminate the inhibition of photosynthesis caused by O 2 in water-stress-sensitive plants such as Phaseolus vulgaris. To investigate the lack of O 2 inhibition of photosynthesis, we measured stromal and cytosolic fructose-1,6-bisphosphatase, sucrose phosphate synthase, and partitioning of newly fixed carbon between starch and sucrose before, during, and after mild water stress. The extractable activity of the fructose bisphosphatases was unaffected by mild water stress. The extractable activity of SPS was inhibited by more than 60% in plants stressed to water potentials of −0.9 megapascals. Water stress caused a decline in the starch/sucrose partitioning ratio indicating that starch synthesis was inhibited more than sucrose synthesis. We conclude that the reduced rate of photosynthesis during water stress is caused by stomatal closure, and that the restriction of CO 2 supply caused by stomatal closure leads to a reduction in the capacity for both starch and sucrose synthesis. This causes the reduced O 2 inhibition and abrupt CO 2 saturation of photosynthesis. 相似文献
19.
CO 2 concentrations of 1000 compared to 350 microliters per liter in controlled environment chambers did not increase total fruit weight or number in a monoecious cucumber ( Cucumis sativus L. cv Chipper) nor did it increase biomass, leaf area, or relative growth rates beyond the first 16 days after seeding. Average fruit weight was slightly, but not significantly greater in the 1000 microliters per liter CO 2 treatment because fruit numbers were changed more than total weight. Plants grown at 1000 and 350 microliters per liter CO 2 were similar in distribution of dry matter and leaf area between mainstem, axillary, and subaxillary branches. Early flower production was greater in 1000 microliters per liter plants. Subsequent flower numbers were either lower in enriched plants or similar in the two treatments, except for the harvest at fruiting when enriched plants produced many more male flowers than the 350 microliters per liter treatments. 相似文献
20.
Water hyacinth ( Eichhornia crassipes [Mart.] Solms) plants were grown in environmental chambers at ambient and enriched CO 2 levels (330 and 600 microliters CO 2 per liter). Daughter plants (ramets) produced in the enriched CO 2 gained 39% greater dry weight than those at ambient CO 2, but the original mother plants did not. The CO 2 enrichment increased the number of leaves per ramet and leaf area index, but did not significantly increase leaf size or the number of ramets formed. Flower production was increased 147%. The elevated CO 2 increased the net photosynthetic rate of the mother plants by 40%, but this was not maintained as the plants acclimated to the higher CO 2 level. After 14 days at the elevated CO 2, leaf resistance increased and transpiration decreased, especially from the adaxial leaf surface. After 4 weeks in elevated as compared to ambient CO 2, ribulose bisphosphate carboxylase activity was 40% less, soluble protein content 49% less, and chlorophyll content 26% less; whereas starch content was 40% greater. Although at a given CO 2 level the enriched CO 2 plants had only half the net photosynthetic rate of their counterparts grown at ambient CO 2, they showed similar internal CO 2 concentrations. This suggested that the decreased supply of CO 2 to the mesophyll, as a result of the increased stomatal resistance, was counterbalanced by a decreased utilization of CO 2. Photorespiration and dark respiration were lower, such that the CO 2 compensation point was not altered. The photosynthetic light and CO 2 saturation points were not greatly changed, nor was the O 2 inhibition of photosynthesis (measured at 330 microliters CO 2 per liter). It appears that with CO 2 enrichment the temporary increase in net photosynthesis produced larger ramets. After acclimation, the greater total ramet leaf area more than compensated for the lower net photosynthetic rate on a unit leaf area basis, and resulted in a sustained improvement in dry weight gain. 相似文献
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