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1.
The depressions of photosynthetic CO 2 uptake following O 3 exposures of 200 and 400 nmol mol -1 for between 4 and 16 h were compared between Pisum sativum, Quercus robur and Triticum aestivum, and the potential causes of change identified in vivo. Photosynthetic change was examined by analysis of CO 2, O 2, O 3 and water vapour exchanges together with chlorophyll fluorescence in controlled environments. Under identical fumigation conditions, each species showed very similar rates of O 3 consumption. The light-saturated rate of CO 2 uptake showed a statistically significant decrease in each species with increasing O 3 dose. Although stomatal conductance declined in parallel with CO 2 uptake this did not account for the observed decrease in photosynthesis. The decrease in mesophyll conductance resulted primarily from a decrease in the apparent carboxylation capacity, implying in decreased activity of ribulose 1,5-bisphosphate carboxylase/oxygenase. The maximum capacity of carboxylation was consequently reduced by over 30% and 50% after 16 h fumigation with 200 and 400 nmol mol -1 O 3 respectively. Additionally, in Q. robur, a statistically significant inhibition of the CO 2 saturated rate of photosynthesis occurred after 16 h with 400 nmol mol -1 O 3, suggesting that the ability to regenerate ribulose 1,5-bisphosphate was also impaired. None of the species showed any significant decrease in the efficiency of light-limited photosynthesis following fumigation at 200 nmol mol -1 O 3, but effects were apparent at 400 nmol mol -1 O 3. The common feature in all three species was a decline in carboxylation capacity which preceded any other change in the photosynthetic apparatus.Abbreviations A sat
net CO 2 uptake rate per unit leaf area at light saturation
- A
net CO 2 uptake rate per unit leaf area
- A max
net CO 2 uptake rate per unit leaf area at CO 2 and light saturation
- c i
mole fraction of CO 2 in the intercellular air space
- g s
stomatal conductance to CO 2
- F m
maximum chlorophyll fluorescence
- F v
variable chlorophyll fluorescence
- c
quantum yield of CO 2 uptake for absorbed light
- 0
quantum yield of oxygen evolution for incident light
- PPFD
photosynthetically active radiation
- Rubisco
ribulose 1,5-bisphosphate carboxylase/oxygenase
- RuBP
ribulose 1,5-bisphosphate
- Vc max
maximum rate of carboxylation 相似文献
2.
Assimilatory power was measured in ten C 3 species by means of a rapid-response gas exchange device as the total amount of CO 2 fixed in N 2-CO 2 atmosphere after switching the light off. Different steady-state levels of the assimilatory power were obtained by varying light intensity and O 2 and CO 2 concentrations during the preexposition periods in the leaf chamber. Within the limits of the linear part of the CO2 curve of photosynthesis in N2, the assimilatory power is constant, being sufficient for the assimilation of about 20 nanomoles CO2 per square centimeter leaf. The pool starts to decrease with the onset of the CO2 saturation of photosynthesis. Increase in O2 concentration from 0 to 100% at 350 microliters CO2 per liter produces a considerable decrease in the assimilatory power. The mesophyll conductance (M) was found to be proportional to the assimilatory power (A): M = mA. The most frequently occurring values of the proportionality constant (m) (called the specific efficiency of carboxylation) were concentrated between 0.03 and 0.04 centimeter per second per nanomole A per square centimeter but the measured extreme values were 0.01 and 0.06 centimeter per second per nanomole A per square centimeter. The specific rate of carboxylation (the rate per unit A) showed a hyperbolic dependence on CO2 conentration with the most frequent values of Km (CO2) ranging from 25 to 35 micromolar in the liquid phase of mesophyll cells (extremes 23 and 100 micromolar). It is concluded that the CO2− and light-saturated rate of photosynthesis is limited by the reactions of the formation of the assimilatory power and not by ribulose-1,5-bisphosphate carboxylase. O2 is a competitive consumer of the assimilatory power, and the inhibitory effect of O2 on photosynthesis is caused mainly by a decrease in the pool of the assimilatory power at high O2 concentrations. In intact leaves, the kinetic properties of ribulose-1,5-bisphosphate carboxylase seem to be variable. 相似文献
3.
Recalculations of soybean photorespiration indicate that mean rates are closer to 16.1 than 5.6 milligrams of CO 2 per square decimeter per hour as previously reported. Photorespiration of soybean thus amounts to at least a 30% carbon turnover of light-saturated photosynthesis. Photorespiration showed no significant relationship to net photosynthesis. Negative correlations were found between CO 2 efflux and stomatal resistance as well as between corrected photorespiration and residual intracellular resistance of the leaf to CO 2 uptake. 相似文献
4.
The quantum requirement (QR) for photosynthesis in Sedum praealtum, a Crassulacean acid metabolism plant, was compared with that of wheat, a C 3 plant, and maize, a C 4 plant, at 30 C. During the deacidification phase in S. praealtum, approximately 16 moles quanta were absorbed per mole malate consumed. This is equivalent to 16 moles quanta per mole CO 2 fixed, assuming 1 mole CO 2 is assimilated per mole malate decarboxylated. This QR for Crassulacean acid metabolism is similar to that of the C 3 or C 4 plant under atmospheric conditions, even though there are considerable differences in the biochemistry of photosynthesis. During late-afternoon C 3-like fixation of atmospheric CO 2 in S. praealtum, the QR was relatively high with values of 41 under 21% O 2 and 19 under 2% O 2. During the deacidification phase in S. praealtum, the relatively low QR can be accounted for by the repression of photorespiration and saturation of photosynthesis from the elevated CO 2 concentration in the leaves during malate decarboxylation. 相似文献
5.
As part of an ongoing investigation into the effects of long-term UV-B radiation exposure on the growth and morphology of
woody perennials, the gas exchange and photosynthesis of five common deciduous tree species were measured. All five tree species
had been exposed to UV-B radiation for 5 years, in the field, at an enhancement level equivalent to an 18% ozone depletion.
Measurements made during the fifth year of UV-B irradiation recorded reductions in light-saturated photosynthesis, transpiration
and water use efficiencies. These changes were accompanied by marked reductions in individual leaf areas, stomatal density,
stomatal conductance and carboxylation efficiency. There were no significant changes in the maximum variable fluorescence
ratio, the quantum requirement of oxygen evolution, or light-saturated O 2 production. Analysis of the response of net carbon assimilation to changing intercellular CO 2 concentration (A/c i response) demonstrated no significant change in stomatal limitation. Reductions in photosynthesis were consistent with decreased
carboxylation efficiency. Although all five tree species were similarly affected by UV-B radiation treatment, the magnitude
of the responses was species-specific. These findings demonstrate the need for more long-term experimentation and also suggest
that changes in water use efficiency may be a significant factor in plants' responses to UV-B radiation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
6.
Portulacaria afra (L.) Jacq., a perennial facultative Crassulacean acid metabolism (CAM) species, was studied under natural photoperiods and temperatures in San Diego, California. The plants were irrigated every fourth day throughout the study period. Measurements of 14CO 2 uptake, stomatal resistance, and titratable acidity were made periodically from July 1981 through May 1982. P. afra maintained C 3 photosynthesis during the winter and the spring. Diurnal acid fluctuations were low and maximal 14CO 2 uptake occurred during the day. The day/night ratio of carbon uptake varied from 5 to 10 and indicated little nocturnal CO 2 uptake. CAM photosynthesis occurred during the summer and a mixture of both C 3 and CAM during the fall. Large acid fluctuations of 100 to 200 microequivalents per gram fresh weight were observed and maximal 14CO 2 uptake shifted to the late night and early morning hours. Daytime stomatal closure was evident. A reduction in the day/night ratio of carbon uptake to 2 indicated a significant contribution of nocturnal CO 2 uptake to the overall carbon gain of the plant. The seasonal shift from C 3 to CAM was facilitated by increasing daytime temperature and accompanied by reduced daytime CO 2 uptake despite irrigation. 相似文献
7.
Nocturnal CO 2 uptake by a Crassulacean acid metabolism succulent, Agave deserti Engelm. (Agavaceae), was measured so that the resistance properties of the mesophyll chlorenchyma cells and their CO 2 concentrations could be determined. Two equivalents of acidity were produced at night per mole of CO 2 taken up. The nocturnal CO 2 uptake became light-saturated at 3.5 mEinsteins cm −2 of photosynthetically active radiation (400-700 nm) incident during the preceding day; at least 46 Einsteins were required per mole of CO 2 fixed. Variations in the daytime leaf temperature between 20 and 37 C had little effect on nocturnal CO 2 uptake. After the first few hours in the dark, the leaf liquid phase CO 2 resistance (r liqCO2) and the CO 2 concentration in the chlorenchyma cells (c iCO2) both increased, the latter usually reaching the ambient external CO 2 level at the end of the dark period. Increasing the leaf surface temperature above 15 C at night markedly increased the stomatal resistance, r liqCO2, and c iCO2. The minimum rliqCO2 at night was about 1.6 seconds cm−1. Based on the ratio of chlorenchyma surface area to total leaf surface area of 82, this rliqCO2 corresponded to a minimum cellular resistance of approximately 130 seconds cm−1, comparable to values for mesophyll cells of C3 plants. The contribution of the carboxylation reaction and/or other biochemical steps to rliqCO2 may increase appreciably as the nighttime temperature shifts a few degrees from the optimum or after a few hours in the dark, both of which caused large increases in rliqCO2. This necessitates a large internal leaf area for CO2 diffusion into the chlorenchyma to support moderate nocturnal CO2 uptake rates by these succulent leaves. 相似文献
8.
CO 2 concentration was elevated throughout 3 years around stands of the C 3 sedge Scirpus olneyi on a tidal marsh of the Chesapeake Bay. The hypothesis that tissues developed in an elevated CO 2 atmosphere will show an acclimatory decrease in photosynthetic capacity under light-limiting conditions was examined. The absorbed light quantum yield of CO 2 uptake (ø abs and the efficiency of photosystem II photochemistry were determined for plants which had developed in open top chambers with CO 2 concentrations in air of 680 micromoles per mole, and of 351 micromoles per mole as controls. An Ulbricht sphere cuvette incorporated into an open gas exchange system was used to determine ø abs and a portable chlorophyll fluorimeter was used to estimate the photochemical efficiency of photosystem II. When measured in an atmosphere with 10 millimoles per mole O 2 to suppress photorespiration, shoots showed a ø abs of 0.093 ± 0.003, with no statistically significant difference between shoots grown in elevated or control CO 2 concentrations. Efficiency of photosystem II photochemistry was also unchanged by development in an elevated CO 2 atmosphere. Shoots grown and measured in 680 micromoles per mole of CO 2 in air showed a ø abs of 0.078 ± 0.004 compared with 0.065 ± 0.003 for leaves grown and measured in 351 micromoles per mole CO 2 in air; a highly significant increase. In accordance with the change in ø abs, the light compensation point of photosynthesis decreased from 51 ± 3 to 31 ± 3 micro-moles per square meter per second for stems grown and measured in 351 and 680 micromoles per mole of CO 2 in air, respectively. The results suggest that even after 3 years of growth in elevated CO 2, there is no evidence of acclimation in capacity for photosynthesis under light-limited conditions which would counteract the stimulation of photosynthetic CO 2 uptake otherwise expected through decreased photorespiration. 相似文献
9.
The rate of CO 2 assimilation and levels of metabolites of the C 4 cycle and reductive pentose phosphate pathway in attached leaves of maize ( Zea mays L.) were measured over a range of light intensity from 0 to 1,900 microEinsteins per square meter per second under a saturated CO 2 concentration of 350 microliters per liter and a limiting CO 2 concentration of 133 microliters per liter. The level of ribulose 1,5-bisphosphate (RuBP) stayed almost constant (around 60 nanomoles per milligram chlorophyll [Chl]) from low to high light intensities under 350 microliters per liter. Levels of 3-phosphoglycerate (PGA) increased from 100 to 650 nanomoles per milligram Chl under 350 microliters per liter CO 2 with increasing light intensity. The calculated RuBP concentration of 6 millimolar (corresponded to 60 nanomoles per milligram Chl) was about two times above the estimated RuBP binding-site concentration on ribulose bisphosphate carboxylase-oxygenase (Rubisco) of ~2.6 millimolar in maize bundle sheath chloroplasts in the light. The ratio of RuBP/PGA increased with decreasing light intensity under 350 microliters per liter CO 2. These results suggest that RuBP carboxylation is under control of light intensity possibly due to a limited supply of CO 2 to Rubisco through the C 4 cycle whose activity is highly dependent on light intensity. Pyruvate level increased with increasing light intensity as long as photosynthesis rate increased. A positive relationship between levels of PGA and those of pyruvate during steady-state photosynthesis under various conditions suggests that an elevated concentration of PGA increases the carbon input into the C 4 cycle through the conversion of PGA to PEP and consequently the level of total intermediates of the C 4 cycle can be raised to mediate higher photosynthesis rate. 相似文献
10.
Wheat ( Triticum aestivum L. cv Albis) was grown in open-top chambers in the field and fumigated daily with charcoal-filtered air (0.015 microliters per liter O 3), nonfiltered air (0.03 microliters per liter O 3), and air enriched with either 0.07 or 0.10 microliters per liter ozone (seasonal 8 hour/day [9 am-5 pm] mean ozone concentration from June 1 until July 10, 1987). Photosynthetic 14CO 2 uptake was measured in situ. Net photosynthesis, dark respiration, and CO 2 compensation concentration at 2 and 21% O 2 were measured in the laboratory. Leaf segments were freeze-clamped in situ for the determination of the steady state levels of ribulose 1,5-bisphosphate, 3-phosphoglycerate, triose-phosphate, ATP, ADP, AMP, and activity of ribulose, 1,5-bisphosphate carboxylase/oxygenase. Photosynthesis of flag leaves was highest in filtered air and decreased in response to increasing mean ozone concentration. CO 2 compensation concentration and the ratio of dark respiration to net photosynthesis increased with ozone concentration. The decrease in photosynthesis was associated with a decrease in chlorophyll, soluble protein, ribulose bisphosphate carboxylase/oxygenase activity, ribulose bisphosphate, and adenylates. No decrease was found for triose-phosphate and 3-phosphoglycerate. The ratio of ATP to ADP and of triosephosphate to 3-phosphoglycerate were increased suggesting that photosynthesis was limited by pentose phosphate reductive cycle activity. No limitation occurred due to decreased access of CO 2 to photosynthetic cells since the decrease in stomatal conductance with increasing ozone concentration did not account for the decrease in photosynthesis. Ozonestressed leaves showed an increased degree of activation of ribulose bisphosphate carboxylase/oxygenase and a decreased ratio of ribulose bisphosphate to initial activity of ribulose bisphosphate carboxylase/oxygenase. Nevertheless, it is suggested that photosynthesis in ozone stressed leaves is limited by ribulose bisphosphate carboxylation possibly due to an effect of ozone on the catalysis by ribulose bisphosphate carboxylase/oxygenase. 相似文献
11.
Plants of Solidago virgaurea L. from exposed and shaded habitats differ with respect to the response of the photosynthetic apparatus to the level of irradiance during growth. An analysis was carried out on leaf characteristies which might be responsible for the differences established in the rates of Hght-saturated CO 2 uptake. The clones were grown in controlled environment chambers at high and low levels of irradiance. Light-saturated rates of photosynthesis and transpiration were measured at natural and lower ambient CO 2 concentrations. A low temperature dependence of light-saturated CO 2 uptake at natural CO 2 concentrations, and a strong response to changes in stomatal width, suggested that the rate of CO 2 transfer from ambient air towards reaetion sites in chloroplasts was mainly limiting the pholosynthetic rate. Resistances to transfer of CO 2 for different parts of the pathway were calculated. There was a weak but significant correlation between stomatal conductance and the product stomatal frequency ± pore length. Mesopbyll conductance and dry weight per unit area were highly correlated in leaves not damaged by high irradiance. This suggests that mesophyll conductance increases with increasing cross sectional area (per unit leaf area) of the pathways of CO 2 transfer in the mesophyll from cell surfaces to reaction sites. The higher light-saturated photosynthesis in clones from exposed habitats when grown at high irradiance than when grown at low irradiance was attributable mainly to a lower mesophyll resistance. In shade clones the effect upon CO 2 uptake of the increase in leaf thickness when grown at high irradiance was counteracted by the associated inactivation of the photosynthetic apparatus. The difference in CO 2 uptake present between clones from exposed and shaded habitats when preconditioned to high irradiance resulted from differences in both mesophyll and stomatal resistances. A few hybrid clones of an F 1-population from a cross between a clone from an exposed habitat and a clone from a shaded habitat reacted, on the whole, in the same way as the exposed habitat parent. When grown at high irradiance, the hybrid clones showed higher photosynthetic rates than either parent; this was largely attributable to the unusually low stomatal resistance of the hybrid leaves. 相似文献
12.
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
13.
Nitrogen (N) availability is a critical factor affecting photosynthetic acclimation of C 3 plants under elevated atmospheric CO 2 concentration ([CO 2] e). However, current understanding of N effects on photosynthetic electron transport rate and partitioning, as well as its impact on photosynthesis under [CO 2] e, is inadequate. Using controlled environment open-top chambers, wheat ( Triticum aestivum L.) was grown at two N levels (0 and 200 mg(N) kg ?1 soil) and two atmospheric CO 2 concentrations of 400 ([CO 2] a) and 760 μmol mol ?1([CO 2] e) during 2009 and 2010. Under [CO 2] e high N availability increased stomatal conductance and transpiration rate, reduced limitations on the activity of triose phosphate isomerase, a Calvin cycle enzyme, and increased the rate of net photosynthesis ( P N). Considering photosynthetic electron transport rate and partitioning aspects, we suggest that greater N availability increased P N under [CO 2] e due to four following reasons: ( 1) higher N availability enhanced foliar N and chlorophyll concentrations, and the actual photochemical efficiency of photosystem (PS) II reaction centers under irradiance increased, ( 2) increase of total electron transport rate and proportion of open PSII reaction centers, ( 3) enhancement of the electron transport rate of the photochemical and carboxylation processes, and ( 4) reduced limitations of the Calvin cycle enzymes on the photosynthetic electron transport rate. Consequently, sufficient N improved light energy utilization in wheat flag leaves under [CO 2] e, thus benefiting to photosynthetic assimilation. 相似文献
14.
Summary Seasonal changes in the photosynthetic characteristics of intact involucral leaves of Anemone raddeana were investigated under laboratory conditions. Net photosynthesis and constant water vapor pressure deficit showed almost the same seasonal trend. They increased rapidly from mid-April immediately after unfolding of the leaves and reached the maximum in late-April, before the maximum expansion of the leaves. They retained the maximum values until early-May and then decreased toward late-May with a progress of leaf senescence. The calculated values of intercellular CO 2 concentration and relative stomatal limitation of photosynthesis showed no significant change throughout the season. The carboxylation efficiency as assessed by the initial slope of Ci-photosynthesis curve and the net photosynthesis under a high Ci regime varied seasonally in parallel with the change of the light-saturated photosynthesis. The results indicate that the seasonal changes in light-saturated net photosynthesis are not due to a change of stomatal conductance, but to a change in the photosynthetic capacity of mesophyll. Nevertheless, leaf conductance changed concomitantly with photosynthetic capacity, indicating that the seasonal change in stomatal conductance is modulated by the mesophyll photosynthetic capacity such that the intercellular CO 2 concentrations is maintained constant. The shape of light-photosynthesis curve was similar to that of sun-leaf type. The quantum yield also changed simultaneously with the photosynthetic capacity throughout the season.Contribution No. 2965 from the Institute of Low Temperature Science 相似文献
15.
Low phosphate nutrition results in increased chlorophyll fluorescence, reduced photosynthetic rate, accumulation of starch and sucrose in leaves, and low crop yields. This study investigated physiological responses of soybean ( Glycine max [L.] Merr.) leaves to low inorganic phosphate (Pi) conditions. Responses of photosynthesis to light and CO 2 were examined for leaves of soybean grown at high (0.50 millimolar) or low (0.05 millimolar) Pi. Leaves of low Pi plants exhibited paraheliotropic orientation on bright sunny days rather than the normal diaheliotropic orientation exhibited by leaves of high Pi soybeans. Leaves of plants grown at high Pi had significantly higher light saturation points (1000 versus 630 micromole photons [400-700 nanometers] per square meter per second) and higher apparent quantum efficiency (0.062 versus 0.044 mole CO 2 per mole photons) at ambient (34 pascals) CO 2 than did low Pi leaves, yet stomatal conductances were similar. High Pi leaves also had significantly higher carboxylation efficiency (2.90 versus 0.49 micromole CO 2 per square meter per second per pascal), a lower CO 2 compensation point (6.9 versus 11.9 pascals), and a higher photosynthetic rate at 34 pascals CO 2 (19.5 versus 6.7 micromoles CO 2 per square meter per second) than did low Pi leaves. Soluble protein (0.94 versus 0.73 milligram per square centimeter), ribulose-1,5-bisphosphate carboxylase/oxygenase content (0.33 versus 0.25 milligram per square centimeter), and ribulose-1,5-bisphosphate carboxylase/oxygenase specific activity (25.0 versus 16.7 micromoles per square meter per second) were significantly greater in leaves of plants in the high Pi treatment. The data indicate that Pi stress alters the plant's CO 2 reduction characteristics, which may in turn affect the plant's capacity to accommodate normal radiation loads. 相似文献
16.
Reduced photorespiration has been reported in Panicum milioides on the basis of lower CO 2 compensation concentrations than in C 3 species, lower CO 2 evolution in the light, and less response of apparent photosynthesis to O 2 concentration. The lower response to O 2 in P. milioides could be due to reduced O 2 competition with CO 2 for reaction with ribulose 1,5-bisphosphate, to a reduced loss of CO 2, or to an initial fixation of CO 2 by phosphoenolpyruvate carboxylase. Experiments were carried out with Panicum maximum Jacq., a C 4 species having no apparent photorespiration; tall fescue ( Festuca arundinacea Schreb.), a C 3 species; P. milioides Nees ex Trin.; and Panicum schenckii Hack. The latter two species are closely related and have low photorespiration rates. CO 2 exchange was measured at five CO 2 concentrations ranging from 0 to 260 microliters per liter at both 2 and 21% O 2. Mesophyll conductance or carboxylation efficiency was estimated by plotting substomatal CO 2 concentrations against apparent photosynthesis. In the C 4 species P. maximum, mesophyll conductance was 0.96 centimeters per second and was unaffected by O 2 concentration. At 21% O 2 mesophyll conductance of tall fescue was decreased 32% below the value at 2% O 2. Decreases in mesophyll conductance at 21% O 2 for P. milioides and P. schenckii were similar to that for tall fescue. On the other hand, loss of CO 2 in CO 2-free air, estimated by extrapolating the CO 2 response curve to zero CO 2, was increased from 1.8 to 6.5 milligrams per square decimeter per hour in tall fescue as O 2 was raised from 2-21%. Loss of CO 2 was less than 1 milligram per square decimeter per hour for P. milioides and P. schenckii and was unaffected by O 2. The results suggest that the reduced O 2 response in P. milioides and P. schenckii is due to a lower loss of CO 2 in the light rather than less inhibition of carboxylation by O 2, since the decrease in carboxylation efficiency at 21% O 2 was similar for P. milioides, P. schenckii, and tall fescue. The inhibition of apparent photosynthesis by 21% O 2 in these three species at low light intensities was similar at 31 to 36% which also indicates similar O 2 effects on carboxylation. Apparent photosynthesis at high light intensity was inhibited less by 21% O 2 in P. milioides (16.8%) and P. schenckii (23.8%) than in tall fescue (28.4%). This lower inhibition in the Panicum species may have been due to a higher degree of recycling of photorespired CO 2 in these species than in tall fescue. 相似文献
17.
Photosynthetic CO 2 and O 2 exchange was studied in two moss species, Hypnum cupressiforme Hedw. and Dicranum scoparium Hedw. Most experiments were made during steady state of photosynthesis, using 18O 2 to trace O 2 uptake. In standard experimental conditions (photoperiod 12 h, 135 micromoles photons per square meter per second, 18°C, 330 microliters per liter CO 2, 21% O 2) the net photosynthetic rate was around 40 micromoles CO 2 per gram dry weight per hour in H. cupressiforme and 50 micromoles CO 2 per gram dry weight per hour in D. scoparium. The CO 2 compensation point lay between 45 and 55 microliters per liter CO 2 and the enhancement of net photosynthesis by 3% O 2versus 21% O 2 was 40 to 45%. The ratio of O 2 uptake to net photosynthesis was 0.8 to 0.9 irrespective of the light intensity. The response of net photosynthesis to CO 2 showed a high apparent Km (CO 2) even in nonsaturating light. On the other hand, O 2 uptake in standard conditions was not far from saturation. It could be enhanced by only 25% by increasing the O 2 concentration (saturating level as low as 30% O 2), and by 65% by decreasing the CO 2 concentration to the compensation point. Although O 2 is a competitive inhibitor of CO 2 uptake it could not replace CO 2 completely as an electron acceptor, and electron flow, expressed as gross O 2 production, was inhibited by both high O 2 and low CO 2 levels. At high CO 2, O 2 uptake was 70% lower than the maximum at the CO 2 compensation point. The remaining activity (30%) can be attributed to dark respiration and the Mehler reaction. 相似文献
18.
Mature, field-grown Vitis vinifera L. grapevines grown in open-top chambers were exposed to either charcoal-filtered air or ambient ozone partial pressures throughout the growing season. Individual leaves also were exposed to ozone partial pressures of 0.2, 0.4, or 0.6 micropascals per pascal for 5 hours. No visual ozone damage was found on leaves exposed to any of the treatments. Chronic exposure to ambient O 3 partial pressures reduced net CO 2 assimilation rate (A) between 5 and 13% at various times throughout the season when compared to the filtered treatment. Exposure of leaves to 0.2 micropascals per pascal O 3 for 5 hours had no significant effect on A; however, A was reduced 84% for leaves exposed to 0.6 micropascals per pascal O 3 when compared to the controls after 5 hours. Intercellular CO 2 partial pressure ( ci) was lower for leaves exposed to 0.2 micropascals per pascal O 3 when compared to the controls, while ci of the leaves treated with 0.6 micropascals per pascal of 0 3 increased during the fumigation. The long-term effects of ambient O 3 and short-term exposure to acute levels of O 3 reduced grape leaf photosynthesis due to a reduction in both stomatal and mesophyll conductances. 相似文献
19.
We compared the CO 2- and light-dependence of photosynthesis of four tree species ( Acer rubrum, Carya glabra, Cercis canadensis, Liquidambar styraciflua) growing in the understory of a loblolly pine plantation under ambient or ambient plus 200 μl l –1 CO 2. Naturally-established saplings were fumigated with a free-air CO 2 enrichment system. Light-saturated photosynthetic rates were 159–190% greater for Ce. canadensis saplings grown and measured under elevated CO 2. This species had the greatest CO 2 stimulation of photosynthesis. Photosynthetic rates were only 59% greater for A. rubrum saplings under CO 2 enrichment and Ca. glabra and L. styraciflua had intermediate responses. Elevated CO 2 stimulated light-saturated photosynthesis more than the apparent quantum yield. The maximum rate of carboxylation of ribulose-1,5-bisphosphate
carboxylase, estimated from gas-exchange measurements, was not consistently affected by growth in elevated CO 2. However, the maximum electron transport rate estimated from gas- exchange measurements and from chlorophyll fluorescence,
when averaged across species and dates, was approximately 10% higher for saplings in elevated CO 2. The proportionately greater stimulation of light-saturated photosynthesis than the apparent quantum yield and elevated rates
of maximum electron transport suggests that saplings growing under elevated CO 2 make more efficient use of sunflecks. The stimulation of light-saturated photosynthesis by CO 2 did not appear to correlate with shade-tolerance ranking of the individual species. However, the species with the greatest
enhancement of photosynthesis, Ce. canadensis and L. styraciflua, also invested the greatest proportion of soluble protein in Rubisco. Environmental and endogenous factors affecting N partitioning
may partially explain interspecific variation in the photosynthetic response to elevated CO 2.
Received: 16 February 1999 / Accepted: 30 August 1999 相似文献
20.
Plants from clonal cuttings of Salix sp. were subjected to a drying cycle of 10 d in a controlled environment. Gas exchange and fluorescence emission were measured on attached leaves. The light-saturated photosynthetic CO 2 uptake became progressively inhibited with decreased leaf water potential both at high, and especially, at low intercellular CO 2 pressure. The maximal quantum yield of CO 2 uptake was more resistant. The inhibition of light-saturated CO 2 uptake at leaf water potentials around-10 bar, measured at a natural ambient CO 2 concentration, was equally attributable to stomatal and non-stomatal factors, but the further inhibition below this water-stress level was caused solely by non-stomatal factors. The kinetics of fluorescence emission was changed at severe water stress; the slow secondary oscillations of the induction curve were attenuated, and this probably indicates perturbations in the carbon reduction cycle. The influence of light level during the drought period was also studied. Provided the leaves were properly light-acclimated, drought at high and low light levels produced essentially the same effects on photosynthesis. However, low-light-acclimated leaves became more susceptible to photoinhibitory treatment under severe water stress, as compared with well-watered conditions. 相似文献
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