JXB Advance Access originally published online on October 22, 2004
Journal of Experimental Botany 2004 55(408):2581-2588; doi:10.1093/jxb/erh260
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RESEARCH PAPER |
A/Ci curve analysis across a range of woody plant species: influence of regression analysis parameters and mesophyll conductance
1USDA Forest Service, PNW Research Station, 3200 Jefferson Way, Corvallis, OR 97331, USA
2Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, USA
* To whom correspondence should be addressed. Fax: +1 541 750 7329. E-mail: dmanter{at}fs.fed.us
Received 1 July 2004; Accepted 21 July 2004
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Abstract |
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The analysis and interpretation of A/Ci curves (net CO2 assimilation rate, A, versus calculated substomatal CO2 concentration, Ci) is dependent upon a number of underlying assumptions. The influence of the Ci value at which the A/Ci curve switches between the Rubisco- and electron transport-limited portions of the curve was examined on A/Ci curve parameter estimates, as well as the effect of mesophyll CO2 conductance (gm) values on estimates of the maximum rate of Rubisco-mediated carboxylation (Vcmax). Based on an analysis using 19 woody species from the Pacific Northwest, significant variation occurred in the Ci value where the Rubisco- and electron transport-limited portions of the curve intersect (Ci_t), ranging from 20 Pa to 152 Pa and averaging c. 71 Pa and 37 Pa for conifer and broadleaf species, respectively. Significant effects on estimated A/Ci parameters (e.g. Vcmax) may arise when preliminary estimates of Ci_t, necessary for the multiple regression analyses, are set either too high or too low. However, when the appropriate threshold is used, a significant relationship between A/Ci and chlorophyll fluorescence estimates of carboxylation is achieved. The use of the Vcmax parameter to describe accurately the Rubisco activity from the A/Ci curve analysis is also dependent upon the assumption that Ci is approximately equal to chloroplast CO2 concentrations (Cc). If leaf mesophyll conductance is low, Cc will be much lower than Ci and will result in an underestimation of Vcmax from A/Ci curves. A large range of mesophyll conductance (gm) values was observed across the 19 species (0.005±0.002 to 0.189±0.011 mol m–2 s–1 for Tsuga heterophylla and Quercus garryana, respectively) and, on average, gm was 1.9 times lower for the conifer species (0.058±0.017 mol m–2 s–1 for conifers versus 0.112±0.020 mol m–2 s–1 for broadleaves). When this mesophyll limitation was accounted for in Vcmax estimates, considerable variation still existed between species, but the difference in Vcmax between conifer and broadleaf species was reduced from c. 11 µmol m–2 s–1 to 4 µmol m–2 s–1. For example, A/Ci curve estimates of Vcmax were 31.2±6.2 and 42.2±4.4 µmol m–2 s–1, and A/Cc curve estimates were 41.2±7.1 µmol m–2 s–1 and 45.0±4.8 µmol m–2 s–1, for the conifer and broadleaf species, respectively.
Key words: A/Ci curve analysis, CO2 assimilation, mesophyll CO2 conductance, photosynthesis, Rubisco, Vcmax
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Introduction |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
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A/Ci curve (net CO2 assimilation rate, A, versus calculated internal CO2 concentrations, Ci) analysis has become a common tool to estimate leaf photosynthesis under a wide variety of experimental conditions (Farquhar et al., 1980
; Wullschleger, 1993, and references therein; Manter et al., 2000). The response function also represents the mechanistic basis behind many plant physiology models (Harley et al., 1992; Manter et al., 2003). While the acquisition of A/Ci response curves is relatively quick and easy to perform, inexpensive (after the initial equipment purchase), and non-destructive, verification of biochemical estimates and analysis assumptions has not been widely tested.
According to the Farquhar et al. (1980) model, carboxylation rates are limited by one of three processes: (i) the amount, activity, and kinetics of Rubisco (Wc), (ii) the rate of ribulose-1,5-bisphosphate regeneration supported by electron transport (Wj), and (iii) occasionally, triose phosphate availability (Wp). Each of these processes can be described mathematically and is expressed at different Ci values. Determination of leaf photosynthesis and gas exchange via A/Ci curve regression analysis necessitates the a priori designation of a Ci threshold at which the A/Ci curve switches between the Rubisco- and electron transport-limited portions of the curve (Ci_t*). It has been well documented that the Wc process occurs at the lowest Ci values (Farquhar et al., 1980) and common values of Ci_t* used for analysis range from 20–25 Pa (Harley et al., 1992; Wullschleger, 1993). However, the effect of Ci_t* values on A/Ci curve parameter estimates have not been well documented, and based on observations working with conifers (Manter et al., 2000; J Kerrigan and DK Manter, unpublished data), it was noted that actual Ci_t values may reach 50 Pa or more and differ markedly between plants.
A second inherent assumption in A/Ci curve analysis is that Ci is approximately equal to that of the catalytic site of Rubisco (Cc). However, limitations to mesophyll CO2 conductance (gm), which are not incorporated in A/Ci measurements, may result in a difference between Ci and Cc. Furthermore, of the limited number of plant species from which gm has been quantified, considerable variation has been observed, ranging from c. 25 mmol m–2 s–1to 400 mmol m–2 s–1 (von Caemmerer and Evans, 1991; Lloyd et al., 1992; Loreto et al., 1992; Epron et al., 1995). As a consequence of this difference in Ci and Cc, Epron et al. (1995) showed that estimates of the maximum rate of carboxylation limited by the amount, activity, and kinetics of Rubisco (Vcmax) from A/Ci curves may be lower than those determined from A/Cc curves (Vcmax_ACc). Finally, much of the variation in Vcmax values across species groups (i.e. broadleaves > conifers) (Wullschleger, 1993) may be associated with unaccounted differences in gm and an underestimation of the actual Rubisco activity using the Vcmax parameter, since a similar pattern in gm has also been reported (broadleaves > conifers) (Evans et al., 1986; von Caemmerer and Evans, 1991; Lloyd et al., 1992; Loreto et al., 1992; Epron et al., 1995). The purpose of this study was to examine specific parameters involved with leaf photosynthesis and gas exchange measurements to optimize A/Ci analysis and estimates of associated processes. The primary objectives were to (i) determine the influence of Ci_t* values on A/Ci curve parameter estimates and (ii) examine the effect of mesophyll CO2 conductance (gm) values on estimates of the maximum rate of Rubisco-mediated carboxylation (Vcmax) and compare A/Ci and A/Cc curve estimates. Nineteen woody plant species from the Pacific Northwest were used for measurements, and differences between coniferous and broadleaf species were noted.
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Materials and methods |
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Plant material
One- and two-year-old potted seedlings of various Pacific Northwest species were obtained from local nursery stock in the spring and grown under ambient conditions in an outdoor cold-frame on the Oregon State University campus in Corvallis. Plants were irrigated as needed and fertilized with Osmocote Pro 18-8-8 (Scotts-Sierra Horticultural Products Co., Marysville, OH). The 19 species were Abies concolor (Gordon & Glend.) Lindl. ex Hildebr. (white fir), Abies grandis (Douglas ex D. Don) Lindl. (grand fir), Abies magnifica Andr. Murray (California red fir), Abies procera Rehd. (noble fir), Acer circinatum Pursh (vine maple), Acer macrophyllum Pursh (big leaf maple), Alnus rhombifolia Nutt. (white alder), Alnus rubra Bong. (red alder), Corylus cornuta Marsh (beaked hazel), Larix occidentalis Nutt. (western larch), Pinus lambertiana Douglas (sugar pine), Pinus monticola Douglas ex D. Don (western white pine), Populus trichocarpaxdeltoides (hybrid poplar), Pseudotsuga menziesii (Mirb.) Franco (Douglas-fir), Quercus garryana Douglas (Oregon white oak), Quercus rubra L. (northern red oak), Rhododendron macrophyllum D. Don ex G. Don (Pacific rhododendron), Rhododendron occidentale (Torr. & A. Gray) A. Gray (western azalea), and Tsuga heterophylla (Raf.) Sarg. (western hemlock).
A/Ci curves and fluorescence
Simultaneous measurements of A/Ci response curves and chlorophyll fluorescence were measured on current-year foliage (c. 2 cm2 one-sided projected leaf area) from seedlings (n=2–3) of each species using a Li-Cor 6400 portable photosynthesis system (Open System Vers. 4.0, Li-Cor, Inc., Lincoln, NE) within a 10 d period in July. Cuvette conditions were maintained at a photosynthetic photon flux density (PPFD) of 1600 µmol m–2 s–1, relative humidity >60%, and a leaf temperature of 25 °C. Leaf temperatures were measured directly for broadleaf species and calculated using the energy balance method for conifer species. Ambient CO2 concentration (Ca) in the cuvette was controlled with a CO2 mixer across the series of 30, 20, 10, 40, 50, 60, 80, 100, 160, and 200 Pa, and measurements were recorded after equilibration to a steady state (coefficient of variation 
2%). CO2 leakage into and out of the empty cuvette was determined at each reference Ca value and used to correct measured leaf fluxes using the equations provided in the Li-Cor operator's manual (see also Bernacchi et al., 2002). Following measurements, one-sided projected leaf area for conifers (broadleaf species' leaves were large enough to fill the entire cuvette) were estimated by placing needles between glass plates and digitally estimating leaf area (Agimage, Decagon Devices, Pullman, WA).
Non-linear regression techniques, based on the equations of Farquhar et al. (1980) and later modified by Sharkey (1985) and Harley and Sharkey (1991), were used to estimate Vcmax, Jmax (the maximum rate of carboxylation limited by electron transport), and Rday (rate of respiration in the presence of light) for each A/Ci curve. In some cases, carboxylation may also be limited by triose phosphate availability (Sharkey, 1985; Harley and Sharkey, 1991); however, this was not observed in any of the plants measured in the study. As discussed elsewhere (Harley et al., 1992; Wullschleger, 1993), it is necessary first to estimate the Wc curve (i.e. Vcmax and Rday) by selecting Ci values below some threshold (i.e. Ci_t*), where it is assumed that A is limited by the amount, activity, and kinetic properties of Rubisco, and then to use the remaining portion of the A/Ci curve to solve for the Wj curve and Jmax. Typical Ci_t* values of 20–25 Pa have been suggested (Wullschleger, 1993), but the consistency with which Ci_t* values occur within this range and their influence on A/Ci curve parameter estimates have not received much attention.
To examine the influence of Ci_t* values, two Vcmax estimates were determined. The first estimate (Vcmax_ACi1) was calculated using a constant Ci_t*=25 Pa. The second estimate (Vcmax_ACi2) was calculated using a variable Ci_t* (i.e. increasing the Ci_t* value such that each successively higher Ca set-point was included in a new analysis), where the appropriate Ci_t* value resulted in the lowest regression mean square statistic. For each Vcmax estimate above, the carboxylation rate at Ca=40 Pa (Wc_ACi) was calculated from equation (1)
 | (1) |
upon illumination with a 0.8 s 7000 µmol m–2 s–1 saturation flash were also measured. Electron transport rate (J) was calculated according to equation (2)
 | (2) |
leaf is leaf absorptance, which was assumed to be 85% (a typical value for C3 plants; Ehleringer and Pearcy, 1983), and the 0.5 factor assumes equal distribution of electrons between PSII and PSI (actual range may vary between 0.4 and 0.6; Ögren and Evans, 1993; Laisk and Loreto, 1996; Albertsson, 2001). The carboxylation rate at Ca=40 Pa (Wc_fluor) was then calculated from equation (3)
 | (3) |
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Estimation of gm and A/Cc curve analysis
Because of recent evidence that suggests Vcmax estimated from A/Ci curves may be underestimated when mesophyll conductance is low and Cc is less than Ci (Epron et al., 1995; Centritto et al., 2003), estimates of gm and maximum Rubisco-mediated carboxylation (Vcmax_ACc) were also derived from A/Cc curves. For estimation of gm the method outlined in Epron et al. (1995) was used. Briefly, an in vivo Rubisco specificity factor (S*) was determined as the slope of the linear regression, forced through the origin, between Jc/Jo and Ci/O, where Jc/Jo is the ratio of electron flow devoted to carboxylation and oxygenation measured by chlorophyll fluorescence and Ci/O is the ratio of the CO2 and O2 mole fractions in the intercellular space (Fig. 1A). In some cases, this relationship was not linear, so the initial slope (Ca <60 Pa) was used to calculate S* (Fig. 1B). Next, gm was calculated from equations (4) and (5)
 | (4) |
 | (5) |
, and references therein). Over this range of S values, estimates of Cc values from equation 4 will be underestimated by 21.9% if S is actually 2100 mol mol–1, and overestimated by 13.2% if S is actually 2950 mol mol–1; estimates of gm from equation 5 will be underestimated by 26.4% if S is actually 2100 mol mol–1, and overestimated by 11.2% if S is actually 2950 mol mol–1. Finally, Vcmax_ACc was determined from the newly derived A/Cc curve using the same variable threshold (Cc_t*) technique outlined above for estimation of Vcmax_ACi2.
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Analysis
The Marquardt estimation technique was used for all non-linear regression analysis of A/Ci and A/Cc curves using the PROC NLIN module of SAS (SAS Institute, Cary, NC). Differences in the various Vcmax estimates between conifer (n=9) and broadleaf (n=10) species were tested using the PROC GLM module in SAS, assuming a completely randomized design. All equations describing the relationship between parameters were determined using the curve-fitting tools found in Sigmaplot 2000 (SPSS, Inc., Chicago, IL).
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Results |
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Three distinct A/Ci curve patterns (Fig. 2) reoccurred throughout the analysis of the dataset. The first two patterns were typified by increasing estimates of Vcmax as the Ci_t* value was raised (Fig. 2A, B). Typically any underestimation of the Rubisco-limited portion of the curve was readily apparent upon visual inspection in these two patterns; however, they differed as to whether an electron transport-limited portion of the A/Ci curve was present over the range of Ci values used in this study (cf. Fig. 2A, B). The third general pattern was typified by a decrease in the estimate of Vcmax as Ci_t* values were increased (Fig. 2C). The three pattern types were not limited to any particular species, although conifers appeared to be more sensitive to changes in the Ci_t* values (Fig. 3). It should be noted that the greatest changes (>100% change in Vcmax over the range of Ci_t* values) were easily seen by visual inspection (Fig. 2A), but the average change in Vcmax (c. 40.5% and 25.6% for the conifers and broadleaves, respectively) could not be visually differentiated (Fig. 2C).
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Because of the difficulty in visually selecting the most appropriate A/Ci curve analysis, the regression mean square statistic was used to aid in selection. No apparent pattern in the ‘best-fit’ Ci_t* value was noted either among or within species, and values ranged from 28 to 79 Pa and from 22 to 63 Pa, averaging 46 and 39 Pa, for the conifer and broadleaf species, respectively (Table 1). Similarly, the actual intersection point between the Rubisco- and electron transport-limited portions of the A/Ci curve (Ci_t) varied greatly between plants, ranging from 25 to 152 Pa (average c. 71.Pa) for conifers and from 20 to 78 Pa (average c. 37 Pa) for broadleaves (Table 1).
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The average Vcmax estimates from the two A/Ci curve analysis techniques are shown in Fig. 3. Species estimates spanned a considerable range with both analysis techniques. For example, using the constant Ci_t* technique Vcmax estimates ranged from 8.6 µmol m–2 s–1 (Tsuga heterophylla) to 53.4 µmol m–2 s–1 (Pinus monticola) for the conifers and from 20.0 µmol m–2 s–1 (Rhododendron macrophyllum) to 52.0 µmol m–2 s–1 (Corylus cornuta) for the broadleaves. The range of Vcmax estimates using the variable Ci_t* technique was 10.4 µmol m–2 s–1 (Tsuga heterophylla) to 70.0 µmol m–2 s–1 (Pinus monticola) and 28.2 µmol m–2 s–1 (Acer circinatum) to 68.1 µmol m–2 s–1 (Alnus rubra) for the conifer and broadleaf species, respectively. The percentage change in Vcmax between the two techniques averaged 25.1% and ranged from –19.8% (Pseudotsuga menziesii) to 73.8% (Pinus monticola). Vcmax estimates between conifers and broadleaves were not statistically different (Table 3) despite a difference of c. 10 µmol m–2 s–1. For example, mean values were 26.0±3.9 and 35.9±3.7 µmol m–2 s–1 for the constant Ci_t* technique, and 31.2±6.2 and 42.2±4.4 µmol m–2 s–1 for the variable Ci_t* technique, respectively. Similar results were also observed with other conifer (25±12 µmol m–2 s–1) and broadleaf (47±33 µmol m–2 s–1) species (Wullschleger, 1993
).
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Carboxylation rates derived from the two A/Ci curve analyses (constant or variable Ci_t*) were compared against estimates of carboxylation derived from chlorophyll fluorescence (Wc_fluor) (Fig. 4). Of the two A/Ci curve analysis techniques, the variable Ci_t* technique yielded the greatest similarity to the fluorescence-derived estimates (Fig. 4). The constant Ci_t* technique resulted in greater Wc errors for the conifers; particularly those plants that had lower Vcmax and higher Ci_t values (Fig. 4A).
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In all, nine plants (eight conifers and one broadleaf) exhibited the second analysis pattern described above (Fig. 2B), and as a result Jmax was not determinable. These plants were typified by relatively low values of Vcmax_ACi2 (16.2±2.2 µmol m–2 s–1) and included the following species: Acer macrophyllum (n=1), Abies concolor (n=1), Abies grandis (n=2), Abies procera (n=1), Pseudotsuga menziesii (n=1), and Tsuga heterophylla (n=3). Despite the wide range in values of Vcmax_ACi2 and Jmax_ACi2, a single, consistent linear relationship was observed (Fig. 5).
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Epron et al. (1995)
noted that the presence of low gm values would result in an underestimation of Vcmax from A/Ci curve analyses because Ci is greater than Cc. They also suggested that conifers have, on average, lower gm values compared with broadleaf species, which may account for some of the frequently observed differences in Vcmax between conifer and broadleaf species (Wullschleger, 1993). Estimates of gm and Vcmax from A/Cc curves suggest that both of these hypotheses are correct. Like the Vcmax estimates, a wide range in gm was observed across species, ranging from 0.005 mol m–2 s–1 (Tsuga heterophylla) to 0.145 mol m–2 s–1 (Pinus monticola) and 0.024 mol m–2 s–1 (Populus trichocarpaxdeltoides) to 0.189 mol m–2 s–1 (Quercus garryana) for the conifer and broadleaf species, respectively (Table 2). On average gm was 1.9-times lower for the conifer (0.058±0.017 mol m–2 s–1) species as compared with the broadleaf (0.112±0.020 mol m–2 s–1) species.
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For all species, accounting for gm limitations and the difference between Ci and Cc often resulted in a large increase in estimates of Vcmax. As shown in Fig. 4, Vcmax_ACc estimates increased c. 25.5% when averaged across all species, ranging from –1.6% (Quercus garryana) to 92.1% (Abies concolor), when compared with Vcmax_ACi2 estimates. Once the effect of gm limitations was taken into account, the difference in Vcmax between conifer and broadleaf species was reduced from c. 10 µmol m–2 s–1 to 4 µmol m–2 s–1 (Table 3). For example, the mean values of Vcmax_ACc were 41.2±7.1 µmol m–2 s–1 and 45.0±4.8 µmol m–2 s–1 for conifers and broadleaves, respectively.
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Discussion |
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It has been demonstrated that using the variable Ci_t* method is a more appropriate analysis method than using a constant Ci value. A/Ci curve analysis is dependent upon an a priori determination of the Ci value where the Rubisco and electron transport limitations to photosynthesis intersect. A detailed discussion of this parameter's influence on A/Ci curve analysis results has not been previously presented in the scientific literature, although examples of the use of the constant Ci_t* (Wullschelger, 1993
) and variable Ci_t* (Manter et al., 2000) methods may be found. Based on the better fit with chlorophyll fluorescence measurements, which do not depend upon presumptive determinations of Ci_t, the variable Ci_t* method is recommended for analysis of A/Ci curves. The impact of Ci_t* values on A/Ci curve estimates was not always visually apparent, and, on average, the constant Ci_t* method underestimated Vcmax by 25.1% compared with the variable Ci_t* technique.
Despite the wide range of photosynthesis and gas exchange estimates across the 19 woody plant species, some notable relationships were observed. A significant linear relationship occurred between Jmax and Vcmax, and although the relative activity of these two processes appears to be constant across plants, Ci_t values varied greatly. As a result, actual rates of carbon assimilation, when light is saturating, will be limited by the amount, activity, and kinetics of Rubisco more often than electron transport rates (Ci <Ci_t). Since Rubisco may serve as a storage protein and exist in an inactivated form (Cheng and Fuchigami, 2000; Warren et al., 2000, 2003), it is likely that Rubisco activation is being limited in these plants by some other factor.
General differences between conifers and broadleaves were notable. For example, Ci_t was approximately two-times greater (c. 71.0 Pa and 37.1 Pa) and A/Ci curve estimates of Vcmax were 10 µmol m–2 s–1 lower for conifers compared with broadleaves. The lower Vcmax in coniferous species may arise from a variety of other factors, such as less resource allocation to photosynthetic processes (Rubisco and chlorophyll per unit nitrogen), greater amounts of inactivated Rubisco, or lower gm values. Based on simultaneous gas exchange and chlorophyll fluorescence measurements, conifers have, on average, significantly lower gm values as compared with broadleaf species, and once this effect on Cc is accounted for the difference in Vcmax between conifers and broadleaves is reduced to 4 µmol m–2 s–1. Similar results documenting the effect of gm on Vcmax estimates have been found with other species (von Caemmerer et al., 1994; Epron et al., 1995) and conditions (Flexas et al., 2002; Medrano et al., 2002; Centritto et al., 2003). After accounting for this limitation, Vcmax estimates still spanned a wide range across all species (19.1±0.7 for Tsuga heterophylla to 85.7±1.3 µmol m–2 s–1 for Pinus monticola).
The data presented here showed high inter- and intra-species variation for the intersection point at which the A/Ci curve switches from being limited by Rubisco to electron transport processes. Major errors in A/Ci curve analyses may arise from designating this threshold too high or too low and, as a general rule, species with low Vcmax values are more sensitive to estimation errors and exhibit higher Ci_t values. Considerable variation in gm values among species may have contributed to perceived differences in Rubisco kinetics when determined solely from A/Ci curve analyses. Finally, it should be noted that all species were analysed with a set of constant values (e.g. S, leaf, Kc, Ko, and the distribution of electrons between photosystem I and II). These factors have all been shown to vary between species and, as such, will result in unknown errors in estimates of the various parameters reported (e.g. Vcmax, Jmax, and gm). While these assumptions may be increasing the variability of parameter estimates, it does not interfere with the general conclusions that across a range of 19 woody plant species (i) the selection of Ci_t* influences A/Ci curve estimates; (ii) gm is correlated with Vcmax; and (iii) gm limitations may result in substantially lower estimates of Vcmax from A/Ci curves as opposed to A/Cc curves.
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Acknowledgements |
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The authors wish to thank Wendy Sutton and Dr Everett Hansen for supplying plant material and Dr Barbara Bond for use of the Li-Cor 6400.
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Footnotes |
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Abbreviations: A, net CO2 assimilation rate;
leaf, leaf absorptance; Ca, ambient CO2 concentration; Cc, Rubisco catalytic site CO2 concentration; Ci, internal CO2 concentration; Ci_t, actual Ci value at which the A/Ci curve switches between the Rubisco- and electron transport-limited portions of the curve; 
maximal fluorescence upon illumination with a 0.8 s 7000 µmol m–2 s–1 saturation flash; Fs, steady-state fluorescence; gm, mesophyll CO2 conductance; J, electron transport rate; Jc electron transport rate devoted to carboxylation measured by chlorophyll fluorescence; Jmax, A/Ci curve estimate of the maximum rate of carboxylation limited by electron transport; Jo, electron transport rate devoted to oxygenation measured by chlorophyll fluorescence; Kc, Michaelis–Menten coefficient for CO2 binding to Rubisco; Ko, Michaelis–Menten coefficient for CO2 binding to Rubisco; PPFD, photosynthetic photon flux density; Rday, rate of respiration in the presence of light; S, specificity of Rubisco for O2/CO2; Vcmax, maximum rate of carboxylation limited by the amount, activity, and kinetics of Rubisco; Wc, rate of carboxylation limited by the amount, activity, and kinetics of Rubisco; Wj, rate of carboxylation limited by ribulose-1,5-bisphosphate regeneration supported by electron transport; Wp, rate of carboxylation limited by triose phosphate availability. |
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  H. E. Bown, M. S. Watt, E. G. Mason, P. W. Clinton, and D. Whitehead The influence of nitrogen and phosphorus supply and genotype on mesophyll conductance limitations to photosynthesis in Pinus radiata Tree Physiol, September 1, 2009; 29(9): 1143 - 1151. [Abstract] [Full Text] [PDF]
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 A. Monti, G. Bezzi, and G. Venturi Internal conductance under different light conditions along the plant profile of Ethiopian mustard (Brassica carinata A. Brown.) J. Exp. Bot., May 1, 2009; 60(8): 2341 - 2350. [Abstract] [Full Text] [PDF]
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U. Niinemets, A. Diaz-Espejo, J. Flexas, J. Galmes, and C. R. Warren Importance of mesophyll diffusion conductance in estimation of plant photosynthesis in the field J. Exp. Bot., May 1, 2009; 60(8): 2271 - 2282. [Abstract] [Full Text] [PDF]
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J. Flexas, M. Baron, J. Bota, J.-M. Ducruet, A. Galle, J. Galmes, M. Jimenez, A. Pou, M. Ribas-Carbo, C. Sajnani, et al. Photosynthesis limitations during water stress acclimation and recovery in the drought-adapted Vitis hybrid Richter-110 (V. berlandierixV. rupestris) J. Exp. Bot., May 1, 2009; 60(8): 2361 - 2377. [Abstract] [Full Text] [PDF]
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U. Niinemets, A. Diaz-Espejo, J. Flexas, J. Galmes, and C. R. Warren Role of mesophyll diffusion conductance in constraining potential photosynthetic productivity in the field J. Exp. Bot., May 1, 2009; 60(8): 2249 - 2270. [Abstract] [Full Text] [PDF]
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Y. Li, Y. Gao, X. Xu, Q. Shen, and S. Guo Light-saturated photosynthetic rate in high-nitrogen rice (Oryza sativa L.) leaves is related to chloroplastic CO2 concentration J. Exp. Bot., May 1, 2009; 60(8): 2351 - 2360. [Abstract] [Full Text] [PDF]
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J Flexas, A Diaz-Espejo, J. Berry, J Cifre, J Galmes, R Kaldenhoff, H Medrano, and M Ribas-Carbo Analysis of leakage in IRGA's leaf chambers of open gas exchange systems: quantification and its effects in photosynthesis parameterization J. Exp. Bot., April 1, 2007; 58(6): 1533 - 1543. [Abstract] [Full Text] [PDF]
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 A. P. Giri, H. Wunsche, S. Mitra, J. A. Zavala, A. Muck, A. Svatos, and I. T. Baldwin Molecular Interactions between the Specialist Herbivore Manduca sexta (Lepidoptera, Sphingidae) and Its Natural Host Nicotiana attenuata. VII. Changes in the Plant's Proteome Plant Physiology, December 1, 2006; 142(4): 1621 - 1641. [Abstract] [Full Text] [PDF]
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J. Galmes, H. Medrano, and J. Flexas Acclimation of Rubisco specificity factor to drought in tobacco: discrepancies between in vitro and in vivo estimations J. Exp. Bot., November 1, 2006; 57(14): 3659 - 3667. [Abstract] [Full Text] [PDF]
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A. Monti, E. Brugnoli, A. Scartazza, and M. T. Amaducci The effect of transient and continuous drought on yield, photosynthesis and carbon isotope discrimination in sugar beet (Beta vulgaris L.) J. Exp. Bot., March 1, 2006; 57(6): 1253 - 1262. [Abstract] [Full Text] [PDF]
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J. I.L. Morison, E. Gallouet, T. Lawson, G. Cornic, R. Herbin, and N. R. Baker Lateral Diffusion of CO2 in Leaves Is Not Sufficient to Support Photosynthesis Plant Physiology, September 1, 2005; 139(1): 254 - 266. [Abstract] [Full Text] [PDF]
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