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1.
Online carbon isotope discrimination (Δ) and leaf gas exchange measurements were made with control and salt-stressed Zea mays and Andropogon glomeratus, two NADP-ME type C 4 grasses. Linear relationships between Δ and p i/p a (the ratio of intercellular to atmospheric CO 2 partial pressure) were found for control plants which agreed well with theoretical models describing carbon isotope discrimination in C 4 plants. These data provided estimates of , the proportion of CO 2 fixed by phospho enolpyruvate carboxylase which leaks out of the bundle sheath and the component of fractionation due to diffusion in air. Salt-stressed plants had wider variation in Δ for the same or less range in p i/p a. Additional work indicated Δ changed independently of p i/p a in both water- and salt-stressed plants, suggesting a possible diurnal change in as plant water status changed linked to a decrease in the activity of the C 3 photosynthetic pathway relative to C 4 pathway activity. The possible effect of stress-induced changes in on organic matter δ 13 C of C 4 plants is apt to be most apparent in chronically stressed environments. 相似文献
2.
The effects of salinity on growth, stomatal conductance, photosynthetic capacity, and carbon isotope discrimination (Δ) of Gossypium hirsutum L. and Phaseolus vulgaris L. were evaluated. Plants were grown at different NaCl concentrations from 10 days old until mature reproductive structures were formed. Plant growth and leaf area development were strongly reduced by salinity, in both cotton and bean. Stomatal conductance also was reduced by salinity. The Δ always declined with increasing external salinity concentration, indicating that stomatal limitation of photosynthesis was increased. In cotton plant dry matter, Δ correlated with the ratio of intercellular to atmospheric CO 2 partial pressures ( pl/ pa) calculated by gas exchange. This correlation was not clear in bean plants, although Δ showed a more pronounced salt induced decline in bean than in cotton. Possible effects of heterogeneity of stomatal aperture and consequent overestimation of pl as determined from gas exchange could explain these results. Significant differences of Δ between leaf and seed material were observed in cotton and bean. This suggests different patterns of carbon allocation between leaves and seeds. The photon yield of O 2 evolution determined at rate-limiting photosynthetic photon flux density was insensitive to salinity in both species analyzed. The light- and CO 2-saturated rate of CO 2 uptake and O 2 evolution showed a salt induced decline in both species. Possible explanations of this observation are discussed. O 2 hypersensitivity was observed in salt stressed cotton plants. These results clearly demonstrate that the effect of salinity on assimilation rate was mostly due to the reduction of stomatal conductance, and that calculation of pl may be overestimated in salt stressed plants, because of heterogeneity of stomatal aperture over the leaf surface. 相似文献
3.
Observations of nonuniform photosynthesis across leaves cast doubt on internal CO 2 partial pressures (p i) calculated on the assumption of uniformity and can lead to incorrect conclusions about the stomatal control of photosynthesis. The problem can be avoided by measuring p i directly because the assumptions of uniformity are not necessary. We therefore developed a method that allowed p i to be measured continuously in situ for days at a time under growth conditions and used it to investigate intact leaves of sunflower ( Helianthus annuus L.), soybean ( Glycine max L. Merr.), and bush bean ( Phaseolus vulgaris L.) subjected to high or low leaf water potentials (ψ w) or high concentrations of abscisic acid (ABA). The leaves maintained a relatively constant differential (Δp) between ambient CO 2 and measured p i throughout the light period when water was supplied. When water was withheld, ψ w decreased and the stomata began to close, but measured p i increased until the leaf reached a ψ w of −1.76 (bush bean), −2.12 (sunflower) or −3.10 (soybean) megapascals, at which point Δp = 0. The increasing p i indicated that stomata did not inhibit CO 2 uptake and a Δp of zero indicated that CO 2 uptake became zero despite the high availability of CO 2 inside the leaf. In contrast, when sunflower leaves at high ψ w were treated with ABA, p i did not increase and instead decreased rapidly and steadily for up to 8 hours even as ψ w increased, as expected if ABA treatment primarily affected stomatal conductance. The accumulating CO 2 at low ψ w and contrasting response to ABA indicates that photosynthetic biochemistry limited photosynthesis at low ψ w but not at high ABA. 相似文献
4.
Photosynthetic gas exchange, plant-water relations characteristics, and stable carbon isotope discrimination (Δ) were evaluated for five Coffea arabica L. genotypes growing under two soil moisture regimes in the field. The Δ of leaf tissue was strongly correlated ( r = −0.95) with inherent water use efficiency (ratio of assimilation to stomatal conductance; A/g). The variation in inherent water use efficiency (WUE) among genotypes was 30% for plants irrigated weekly. The higher WUE exhibited by some of these plants resulted from reduced g rather than increased photosynthetic capacity at a given g. Withholding irrigation for 1 month caused Δ to decline substantially in expanding leaf tissue of all genotypes. A strong correlation ( r = 0.92) was found between Δ and plant hydraulic efficiency estimated as the ratio of g to the diurnal range in leaf water potential (Ψ l). The Δ values for plants irrigated weekly adequately predicted drought-induced changes in Δ ( r = 0.99) and midday Ψ l ( r = 0.95). The results indicated that Δ might be used to evaluate several aspects of plant performance and response to specific environmental conditions, once suitable background physiological data have been gathered. 相似文献
5.
Elevated CO 2 interactions with other factors affects the plant performance. Regarding the differences between cultivars in response to CO 2 concentrations, identifying the cultivars that better respond to such conditions would maximize their potential benefits. Increasing the ability of plants to benefit more from elevated CO 2 levels alleviates the adverse effects of photoassimilate accumulation on photosynthesis and increases the productivity of plants. Despite its agronomic importance, there is no information about the interactive effects of elevated CO 2 concentration and plant growth regulators (PGRs) on potato ( Solanum tuberosum L.) plants. Hence, the physiological response and source-sink relationship of potato plants ( cvs. Agria and Fontane) to combined application of CO 2 levels (400 vs. 800 µmol mol −1) and plant growth regulators (PGR) [6-benzylaminopurine (BAP) + Abscisic acid (ABA)] were evaluated under a controlled environment. The results revealed a variation between the potato cultivars in response to a combination of PGRs and CO 2 levels. Cultivars were different in leaf chlorophyll content; Agria had higher chlorophyll a, b, and total chlorophyll content by 23, 43, and 23%, respectively, compared with Fontane. The net photosynthetic rate was doubled at the elevated compared with the ambient CO 2. In Agria, the ratio of leaf intercellular to ambient air CO 2 concentrations [C i:C a] was declined in elevated-CO 2-grown plants, which indicated the stomata would become more conservative at higher CO 2 levels. On the other hand, the increased C i:C a in Fontane showed a stomatal acclimation to higher CO 2 concentration. The higher leaf dark respiration of the elevated CO 2-grown and BAP + ABA-treated plants was associated with a higher leaf soluble carbohydrates and starch content. Elevated CO 2 and BAP + ABA shifted the dry matter partitioning to the belowground more than the above-media organs. The lower leaf soluble carbohydrate content and greater tuber yield in Fontane might indicate a more efficient photoassimilate translocation than Agria. The results highlighted positive synergic effects of the combined BAP + ABA and elevated CO 2 on tuber yield and productivity of the potato plants. 相似文献
6.
Background and Aims Benefits to crop productivity arising from increasing CO 2 fertilization may be offset by detrimental effects of global climate change, such as an increasing frequency of drought. Phosphorus (P) nutrition plays an important role in crop responses to water stress, but how elevated CO 2 (eCO 2) and P nutrition interact, especially in legumes, is unclear. This study aimed to elucidate whether P supply improves plant drought tolerance under eCO 2.Methods A soil-column experiment was conducted in a free air CO 2 enrichment (SoilFACE) system. Field pea ( Pisum sativum) was grown in a P-deficient vertisol, supplied with 15 mg P kg −1 (deficient) or 60 mg P kg −1 (adequate for crop growth) and exposed to ambient CO 2 (aCO 2; 380–400 ppm) or eCO 2 (550–580 ppm). Drought treatments commenced at flowering. Measurements were taken of soil and leaf water content, photosynthesis, stomatal conductance, total soluble sugars and inorganic P content (Pi).Key Results Water-use efficiency was greatest under eCO 2 when the plants were supplied with adequate P compared with other treatments irrespective of drought treatment. Elevated CO 2 decreased stomatal conductance and transpiration rate, and increased the concentration of soluble sugars and relative water contents in leaves. Adequate P supply increased concentrations of soluble sugars and Pi in drought-stressed plants. Adequate P supply but not eCO 2 increased root length distribution in deeper soil layers.Conclusions Phosphorus application and eCO 2 interactively enhanced periodic drought tolerance in field pea as a result of decreased stomatal conductance, deeper rooting and high Pi availability for carbon assimilation in leaves. 相似文献
7.
Knowledge gaps regarding potential ontogeny and plant species identity effects on carbon isotope fractionation might lead to misinterpretations of carbon isotope composition (δ 13C) of respired CO 2, a widely-used integrator of environmental conditions. In monospecific mesocosms grown under controlled conditions, the δ 13C of C pools and fluxes and leaf ecophysiological parameters of seven herbaceous species belonging to three functional groups (crops, forage grasses and legumes) were investigated at three ontogenetic stages of their vegetative cycle (young foliage, maximum growth rate, early senescence). Ontogeny-related changes in δ 13C of leaf- and soil-respired CO 2 and 13C/ 12C fractionation in respiration (Δ R) were species-dependent and up to 7‰, a magnitude similar to that commonly measured in response to environmental factors. At plant and soil levels, changes in δ 13C of respired CO 2 and Δ R with ontogeny were related to changes in plant physiological status, likely through ontogeny-driven changes in the C sink to source strength ratio in the aboveground plant compartment. Our data further showed that lower Δ R values (i.e. respired CO 2 relatively less depleted in 13C) were observed with decreasing net assimilation. Our findings highlight the importance of accounting for ontogenetic stage and plant community composition in ecological studies using stable carbon isotopes. 相似文献
8.
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
9.
High transpiration rates were found to affect the photosynthetic capacity of Xanthium strumarium L. leaves in a manner analagous to that of low soil water potential. The effect was also looked for and found in Gossypium hirsutum L., Agathis robusta (C. Moore ex Muell.) Bailey, Eucalyptus microcarpa Maiden, Larrea divaricata Cav., the wilty flacca tomato mutant ( Lycopersicon esculentum (L.) Mill.) and Scrophularia desertorum (Munz) Shaw. Two methods were used to distinguish between effects on stomatal conductance, which can lower assimilation by reducing CO 2 availability, and effects on the photosynthetic capacity of the mesophyll. First, the response of assimilation to intercellular CO 2 pressure ( C
i) was compared under conditions of high and low transpiration. Second, in addition to estimating C
i using the usual Ohm's law analogy, C
i was measured directly using the closed-loop technique of T.D. Sharkey, K. Imai, G.D. Farquhar and I.R. Cowan (1982, Plant Physiol, 60, 657–659). Transpiration stress responses of Xanthium strumarium were compared with soil drought effects. Both stresses reduced photosynthesis at high C
i but not at low C
i; transpiration stress increased the quantum requirement of photosynthesis. Transpiration stress could be induced in small sections of leaves. Total transpiration from the plant did not influence the photosynthetic capacity of a leaf kept under constant conditions, indicating that water deficits develop over small areas within the leaf. The effect of high transpiration on photosynthesis was reversed approximately half-way by returning the plants to low-transpiration conditions. This reversal occurred as fast as measurements could be made (5 min), but little further recovery was observed in subsequent hours.Abbreviations and symbols
A
photosynthetic CO 2 assimilation rate
-
C
a
ambient CO 2 partial pressure
-
C
i
partial pressure of CO 2 inside the leaf
- VPD
leaf-to-air water-vapor pressure difference
This research was begun while the author was a Postdoctoral Research Fellow at the Australian National University, Canberra 相似文献
10.
Carbon-isotope discrimination (Δ) is used to distinguish between different photosynthetic pathways. It has also been shown that variation in Δ occurs among varieties of C 3 species, but not as yet, in C 4 species. We now report that Δ also varies among genotypes of sorghum ( Sorghum bicolor Moench), a C 4 species. The discrimination in leaves of field-grown plants of 12 diverse genotypes of sorghum was measured and compared with their grain yields. Discrimination varied significantly among genotypes, and there was a significant negative correlation between grain yield and Δ. The variation in Δ may be caused by genetic differences in either leakiness of the bundle-sheath cells or by differences in the ratio of assimilation rate to stomatal conductance. At the leaf level, the former should be related to light-use efficiency of carbon fixation and the latter should be related to transpiration efficiency. Both could relate to the yield of the crop. 相似文献
11.
The enzymic fractionation of the stable carbon isotopes of CO 2 (Δco 2) was determined using a purified preparation of ribulose-1,5-bisphosphate (RuBP) carboxylase isolated from cotton (a C 3 plant) leaves. The bicarbonate concentration in the reaction mixture saturated the enzyme and furnished an infinite pool of 12CO 2 and 13CO 2 for enzyme fractionation. The RuBP was 96 to 98% pure. The phosphoglycerate synthesized in the reaction mixtures was purified free of RuBP, phosphoglycolate, and other phosphate esters by column chromatography on Dowex 1-Cl − resin. The average Δco 2 value of −27.1% was determined from five separate experiments. A discussion of the isotope fractionation associated with photosynthetic CO 2 fixation in plants shows that the enzymic fractionation of stable carbon isotopes of CO 2 by RuBP carboxylase is of major importance in determining the δ 13C values of C 3 plants. 相似文献
12.
We aimed to quantify the separate effects of photosynthetic and postphotosynthetic carbon isotope discrimination on δ13C of the fast‐turn‐over carbon pool (water soluble organic carbon and CO 2 emitted from heterotrophic tissues), including their diel variation, along the pathway of carbon transport from the foliage to the base of the stem. For that purpose, we determined δ13C in total and water‐soluble organic matter of the foliage plus δ13C and δ18O in phloem organic matter of twigs and at three heights along the stem of Pinus sylvestris over a nine‐day period, including four measurements per day. These data were related to meteorological and photosynthesis parameters and to the δ13C of stem‐emitted CO 2. In the canopy (foliage and twigs), the δ13C of soluble organic matter varied diurnally with amplitudes of up to 1.9‰. The greatest 13C enrichment was recorded during the night/early morning, indicating a strong influence of starch storage and remobilization on the carbon isotope signatures of sugars exported from the leaves. 13C enrichment of soluble organic matter from the leaves to the twig phloem and further on to the phloem of the stem was supposed to be a result of carbon isotope fractionation associated with metabolic processes in the source and sink tissues. CO 2 emitted from the stem was enriched by 2.3–5.2‰ compared with phloem organic matter. When day‐to‐day variation was addressed, water‐soluble leaf δ13C and twig phloem δ18O were strongly influenced by ci/ ca and stomatal conductance ( Gs), respectively. These results show that both photosynthetic and postphotosynthetic carbon isotope fractionation influence δ13C of organic matter over time, and over the length of the basipetal transport pathway. Clearly, these influences on the δ13C of respired CO 2 must be considered when using the latter for partitioning of ecosystem CO 2 fluxes or when the assessment of δ13C in organic matter is applied to estimate environmental effects in ci/ ca. 相似文献
13.
Peanut ( Arachis hypogaea L. cv. Florunner) was grown from seed sowing to plant maturity under two daytime CO 2 concentrations ([CO 2]) of 360 μmol mol −1 (ambient) and 720 μmol mol −1 (elevated) and at two temperatures of 1.5 and 6.0 °C above ambient temperature. The objectives were to characterize peanut leaf photosynthesis responses to long-term elevated growth [CO 2] and temperature, and to assess whether elevated [CO 2] regulated peanut leaf photosynthetic capacity, in terms of activity and protein content of ribulose bisphosphate carboxylase-oxygenase (Rubisco), Rubisco photosynthetic efficiency, and carbohydrate metabolism. At both growth temperatures, leaves of plants grown under elevated [CO 2] had higher midday photosynthetic CO 2 exchange rate (CER), lower transpiration and stomatal conductance and higher water-use efficiency, compared to those of plants grown at ambient [CO 2]. Both activity and protein content of Rubisco, expressed on a leaf area basis, were reduced at elevated growth [CO 2]. Declines in Rubisco under elevated growth [CO 2] were 27–30% for initial activity, 5–12% for total activity, and 9–20% for protein content. Although Rubisco protein content and activity were down-regulated by elevated [CO 2], Rubisco photosynthetic efficiency, the ratio of midday light-saturated CER to Rubisco initial or total activity, of the elevated-[CO 2] plants was 1.3- to 1.9-fold greater than that of the ambient-[CO 2] plants at both growth temperatures. Leaf soluble sugars and starch of plants grown at elevated [CO 2] were 1.3- and 2-fold higher, respectively, than those of plants grown at ambient [CO 2]. Under elevated [CO 2], leaf soluble sugars and starch, however, were not affected by high growth temperature. In contrast, high temperature reduced leaf soluble sugars and starch of the ambient-[CO 2] plants. Activity of sucrose-P synthase, but not adenosine 5′-diphosphoglucose pyrophosphorylase, was up-regulated under elevated growth [CO 2]. Thus, in the absence of other environmental stresses, peanut leaf photosynthesis would perform well under rising atmospheric [CO 2] and temperature as predicted for this century. 相似文献
14.
In earlier-maturing coffee clones, owing to the shorter time required for fruit filling and ripening, photo-assimilates should be transported to fruits in a period shorter than that found in intermediate- or late-maturing clones. We hypothesised that at a given source-to-sink ratio, a presumably greater sink strength in early-maturing clones relative to intermediate- and late-maturing individuals should be correlated to increased rate of net carbon assimilation ( A) and greater photo-assimilate transport to the fruits. Overall, earlier-maturing clones displayed greater A rates than the intermediate-maturing clones, which, in turn, had higher A than their late counterparts. Changes in A were largely associated with changes in stomatal conductance. Only marginal alterations occurred in the internal-to-ambient CO 2 concentration ratio, the carbon isotope composition ratio, soluble sugars and chlorophyll a fluorescence parameters. Some changes in starch pools were detected among treatments. To the best of our knowledge, this is the first report showing evidence that increased precociousness of fruit growth and maturation results in higher A and thus increased source strength, a fact associated to a large degree with higher stomatal aperture. 相似文献
15.
The effect of low intensity continuous light, e.g., in the High Arctic summer, on plant carbon and hydrogen isotope fractionations
is unknown. We conducted greenhouse experiments to test the impact of light quantity and duration on both carbon and hydrogen
isotope compositions of three deciduous conifers whose fossil counterparts were components of Paleogene Arctic floras: Metasequoia glyptostroboides, Taxodium distichum, and Larix laricina. We found that plant leaf bulk carbon isotopic values of the examined species were 1.75–4.63‰ more negative under continuous
light (CL) than under diurnal light (DL). Hydrogen isotope values of leaf n-alkanes under continuous light conditions revealed a D-enriched hydrogen isotope composition of up to 40‰ higher than in
diurnal light conditions. The isotope offsets between the two light regimes is explained by a higher ratio of intercellular
to atmospheric CO 2 concentration ( C
i/ C
a) and more water loss for plants under continuous light conditions during a 24-h transpiration cycle. Apparent hydrogen isotope
fractionations between source water and individual lipids (ε lipid–water) range from −62‰ ( Metasequoia C 27 and C 29) to −87‰ ( Larix C 29) in leaves under continuous light. We applied these hydrogen fractionation factors to hydrogen isotope compositions of in
situ n-alkanes from well-preserved Paleogene deciduous conifer fossils from the Arctic region to estimate the δ D value in ancient precipitation. Precipitation in the summer growing season yielded a δ D of −186‰ for late Paleocene, −157‰ for early middle Eocene, and −182‰ for late middle Eocene. We propose that high-latitude
summer precipitation in this region was supplemented by moisture derived from regionally recycled transpiration of the polar
forests that grew during the Paleogene warming. 相似文献
16.
To evaluate leaf carbon balance during rapid pod-fill in soybean ( Glycine max [L.] Merrill), measurements were made of CO 2 assimilation at mid-day and changes in specific leaf weight, starch, and sucrose concentrations over a 9-hour interval. Assimilate export was estimated from CO 2 assimilation and leaf dry matter accumulation. Chamber-grown `Amsoy 71' and `Wells' plants were subjected on the day of the measurements to one of six photosynthetic photon flux densities in order to vary CO 2 assimilation rates. Rate of accumulation of leaf dry matter and rate of export both increased as CO2 assimilation rate increased in each cultivar. Starch concentrations were greater in Amsoy 71 than in Wells at all CO2 assimilation rates. At low CO2 assimilation rates, export rates in Amsoy 71 were maintained in excess of 1.0 milligram CH2O per square decimeter leaf area per hour at the expense of leaf reserves. In Wells, however, export rate continued to decline with decreasing CO2 assimilation rate. The low leaf starch concentration in Wells at low CO2 assimilation rates may have limited export by limiting carbon from starch remobilization. Both cultivars exhibited positive correlations between CO2 assimilation rate and sucrose concentration, and between sucrose concentration and export rate. Carbon fixation and carbon partitioning both influenced export rate via effects on sucrose concentration. 相似文献
17.
The relationship between malic acid production and carbon assimilation was examined in the submerged aquatic Crassulacean acid metabolism (CAM) plant, Isoetes howellii Engelmann. Under natural conditions free-CO 2 level in the water was highest at 0600 hours and 14CO 2 assimilation rates in I. howellii were also highest at this time. After 0900 hours there was a similar pattern in (a) rate of free-CO 2 depletion from the water, (b) reduction of carbon assimilation rates, and (c) rate of deacidification in leaves. Rates of daytime deacidification increased under CO 2-free conditions and as irradiance intensity increased. Nighttime CO 2 uptake was estimated to contribute one-third to one-half of the total daily gross carbon assimilation. CO 2 uptake, however, accounted for only one-third to one-half of the overnight malic acid accumulation. Internal respiratory CO 2 may be a substrate for a large portion of overnight acid accumulation as leaves incubated overnight without CO 2 accumulated substantial levels of malic acid. Loss of CAM occurred in emergent leaf tips even though submerged bases continued CAM. Associated with loss of CAM in aerial leaves was an increase in total chlorophyll, a/b ratio, and carotenoids, and a decrease in leaf succulence. δ 13C values of I. howellii were not clearly distinguishable from those for associated non-CAM submerged macrophytes. 相似文献
18.
Carbon oxysulfide (COS) was reinvestigated as an inhibitor of active inorganic carbon transport in cells of Synechococcus PCC7942 adapted to growth at low inorganic carbon. COS inhibited both CO 2 and HCO 3− transport processes in a reversible (in the short term) and mixed competitive manner. The inhibition of COS was established using both silicone oil centrifugation experiments and O 2-evolution studies. The Ki for COS inhibition was 29 micromolar for CO 2 transport and 110 micromolar for HCO 3− transport. These results support a model of inorganic carbon transport with a central CO 2 pump and an inducible HCO 3− utilizing accessory protein which supplies CO 2 to the primary pump. 相似文献
19.
A year round study of photosynthesis and carbon isotope fractionation was conducted with plants of Opuntia phaeacantha Engelm. and Yucca baccata Torr. occurring in natural stands at elevations of 525, 970, 1450 and 1900 m. Plant water potentials and the daytime pattern of 14CO 2 photosynthesis were similar for all cacti along the elevational gradient, despite significant differences in temperature regime and soil water status. Carbon isotope ratios of total tissue and soluble extract fractions were relatively constant throughtout the entire year. Additionally, the σ 13C values were similar in all plants of the same species along the elevational gradient, i.e. −12.5 ± 0.86 ‰ for O. phaeacantha and −15.7 ± 0.95 ‰ for Y. baccata. The results of this study indicate Crassulacean acid metabolism predominates as the major carbon pathway of these plants, which do not facultatively utilize the reductive pentose phosphate cycle of photosynthesis as the primary carboxylation reaction. 相似文献
20.
Carbon isotope discrimination (Δ) was measured in the field on 10 cultivars of common bean ( Phaseolus vulgaris L.). There was substantial variation (more than 2‰) in leaf Δ values and these differences were maintained between vegetative and reproductive developmental stages. These bean lines also exhibited substantial differences in leaf conductance to water vapor, and again these differences were maintained across developmental stages. The differences in leaf conductance were positively correlated with Δ values, whether conductance was measured as total leaf conductance or as the individual conductances of either upper or lower leaf surfaces. The observed differences in leaf conductance were not associated with differences in stomatal density. There were small differences among bean lines in their leaf Kjeldahl nitrogen contents, which is interpreted as indicating that photosynthetic capacity among bean lines was similar. Thus, because Δ values and leaf conductance were positively correlated, these data suggested that there may have been differences among bean lines in the extent to which stomata limited photosynthetic gas exchange rates. 相似文献
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