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1.
We examined factors that limit diurnal and seasonal photosynthesis in Leymus cinereus, a robust tussock grass from shrub-steppes of western North America. Data from plants in a natural stand and in experimental field plots indicate that this bunchgrass has 1) a high photosynthetic capacity, 2) high leaf nitrogen content and high nitrogen-use efficiency, 3) a steep leaf-to-air diffusion gradient for carbon dioxide, which enhances intrinsic water-use efficiency, and 4) photosynthetic tissues that tolerate severe water stress and recover quickly from moderate water stress. Midday depressions of CO2 assimilation (A) and stomatal conductance were slight in plants with plentiful water, but marked in plants subject to moderate water stress. Midday stomatal closure in moderately stressed plants reduced intercellular carbon dioxide concentration (ci) by ≈40 μl liter-1. The maximum rate of A achieved during the day for severely stressed plants (predawn water potential = -4 MPa) was one-third and daily carbon gain per unit leaf area was about one-fourth that of well-watered plants. For plants in the natural stand, CO2-saturated photosynthesis declined almost linearly with decreasing soil water availability over the growing season, whereas there was little effect on A at CO2 ambient levels or on carboxylation efficiency until predawn water potentials reached -1.8 MPa. Nitrogen-use efficiency declined with diminishing soil moisture, but there was no seasonal change in stomatal limitation or instantaneous water-use efficiency as estimated from A vs. ci curves at optimal leaf temperature and moderate atmospheric evaporative demand. Thus, reduced stomatal conductance in response to increased evaporative demand may increase stomatal limitation diumally, but over the growing season, stomatal limitation estimated from A vs. ci curves is relatively constant because maximum stomatal conductance is closely tuned to the CO2 assimilatory capacity of the mesophyll.  相似文献   

2.
In this study it has been shown that increased diffusional resistances caused by salt stress may be fully overcome by exposing attached leaves to very low [CO2] (~ 50 µmol mol?1), and, thus a non‐destructive‐in vivo method to correctly estimate photosynthetic capacity in stressed plants is reported. Diffusional (i.e. stomatal conductance, gs, and mesophyll conductance to CO2, gm) and biochemical limitations to photosynthesis (A) were measured in two 1‐year‐old Greek olive cultivars (Chalkidikis and Kerkiras) subjected to salt stress by adding 200 mm NaCl to the irrigation water. Two sets of ACi curves were measured. A first set of standard ACi curves (i.e. without pre‐conditioning plants at low [CO2]), were generated for salt‐stressed plants. A second set of ACi curves were measured, on both control and salt‐stressed plants, after pre‐conditioning leaves at [CO2] of ~ 50 µmol mol?1 for about 1.5 h to force stomatal opening. This forced stomata to be wide open, and gs increased to similar values in control and salt‐stressed plants of both cultivars. After gs had approached the maximum value, the ACi response was again measured. The analysis of the photosynthetic capacity of the salt‐stressed plants based on the standard ACi curves, showed low values of the Jmax (maximum rate of electron transport) to Vcmax (RuBP‐saturated rate of Rubisco) ratio (1.06), that would implicate a reduced rate of RuBP regeneration, and, thus, a metabolic impairment. However, the analysis of the ACi curves made on pre‐conditioned leaves, showed that the estimates of the photosynthetic capacity parameters were much higher than in the standard ACi responses. Moreover, these values were similar in magnitude to the average values reported by Wullschleger (Journal of Experimental Botany 44, 907–920, 1993) in a survey of 109 C3 species. These findings clearly indicates that: (1) salt stress did affect gs and gm but not the biochemical capacity to assimilate CO2 and therefore, in these conditions, the sum of the diffusional resistances set the limit to photosynthesis rates; (2) there was a linear relationship (r2 = 0.68) between gm and gs, and, thus, changes of gm can be as fast as those of gs; (3) the estimates of photosynthetic capacity based on ACi curves made without removing diffusional limitations are artificially low and lead to incorrect interpretations of the actual limitations of photosynthesis; and (4) the analysis of the photosynthetic properties in terms of stomatal and non‐stomatal limitations should be replaced by the analysis of diffusional and non‐diffusional limitations of photosynthesis. Finally, the C3 photosynthesis model parameterization using in vitro‐measured and in vivo‐measured kinetics parameters was compared. Applying the in vivo‐measured Rubisco kinetics parameters resulted in a better parameterization of the photosynthesis model.  相似文献   

3.
The response of photosynthetic CO2 assimilation to salinization in 19 year old Prunus salicina was evaluated under field conditions for a 3 year period. The observed decline in CO2 assimilation capacity was apparently related to increasing leaf chloride (Cl) content, and independent of changes in leaf carbohydrate status. The response of net CO2 assimilation (A) to leaf intercellular CO2 partial pressure (Ci) indicated that the reduction in the capacity for A with Cl was not the result of decreased stomatal conductance but a consequence of nonstomatal inhibition. The nonstomatal limitations to CO2 assimilation capacity, as determined by the response of A to Ci and biochemical assay, were related to a decline in the activity of ribulose 1,5-bisphosphate carboxylase (Rubpcase) and the pool size of triose phosphate, ribulose 1,5-bisphosphate (Rubp) and phosphoglycerate with increasing salinity. Lack of agreement between the initial slope of the A to Ci response curve and Rubpcase activity suggests the occurrence of heterogeneous stomatal apertures with the high salinity treatment (28 millimolar). Prolonged exposure to chloride salts appeared to increase the Rubp or Pi regeneration limitation, decrease Rubpcase activity and reduce leaf chlorophyll content. Observed changes in the biochemical components of CO2 fixation may, in turn, affect total leaf carbohydrates, which also declined with time and salinity. The reduction in Rubpcase activity was apparently a consequence of a reduced Rubpcase protein level rather than either a regulatory or inhibitory effect.  相似文献   

4.
A unique approach was used to evaluate stomatal and nonstomatal constraints to photosynthesis in 19 naturally occurring, deciduous tree species on xeric, mesic and wetmesic sites in central Pennsylvania, USA, during relatively wet (1990) and dry (1991) growing seasons. All species exhibited significantly decreased stomatal conductance to CO2 (gc) in 1991 compared to 1990. The mesic species had drought related decreases in photosynthesis (A) attributed primarily to increased absolute stomatal limitation to A (Lg), whereas in the wet-mesic species, the absolute mesophyll limitation (Lm) was at least as important as Lg in limiting A during drought. The xeric species maintained relatively high A during drought despite decreased gc. In the xeric and mesic species, Lm decreased and Lg increased during drought due to stomatal closure. From xeric to mesic to wet-mesic, the relative stomatal limitation (Ig) generally decreased faster, and relative mesophyll limitations to A increased faster, with increasing gc suggesting greater photosynthetic capacity (i.e. greater potential maximum A) with increasing drought tolerance rank of species. Few species exhibited a significant drought-related decrease in photosynthetic capacity. The results of this landscape-based study indicate that the interaction of stomatal and nonstomatal limitations of A vary in a manner consistent with species' drought tolerance and site conditions, and that nonstomatal constraints to A in field plants during a moderate, season-long drought were generally not as severe as reported in controlled studies.  相似文献   

5.
Transpiration-induced changes in the photosynthetic capacity of leaves   总被引:18,自引:0,他引:18  
Thomas D. Sharkey 《Planta》1984,160(2):143-150
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 CO2 availability, and effects on the photosynthetic capacity of the mesophyll. First, the response of assimilation to intercellular CO2 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 CO2 assimilation rate - C a ambient CO2 partial pressure - C i partial pressure of CO2 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   

6.
The changes caused by NaCl salinity and jasmonic acid (JA) treatment (8 days) on growth and photosynthesis of barley plants (Hordeum vulgare L., var. Alfa) have been studied. Gas exchange measurements and analysis of enzyme activities were used to study the reactions of photosynthesis to salinity and JA. Both 100 mm NaCl and 25 μm JA treatment led to a noticeable decrease in both the initial slope of the curves representing net photosynthetic rate vs intercellular CO2 concentration and the maximal rate of photosynthesis. The calculated values of the intercellular CO2 concentration, CO2 compensation point, and maximal carboxylating efficiency of ribulose-1,5-bisphosphate carboxylase support the suggestion that biochemical factors are involved in the response of photosynthesis to JA and salinity stress. The activities of phosphoenolpyruvate carboxylase and carbonic anhydrase increased more than twofold. Pretreatment with JA for 4 days before salinization diminished the inhibitory effect of high salt concentration on the growth and photosynthesis. The results are discussed in terms of a possible role of JA in increasing salinity tolerance of the barley plants. Received September 8, 1997; accepted May 19, 1998  相似文献   

7.
Glycerol induced a limitation on photosynthetic carbon assimilation by phosphate when supplied to leaves of barley (Hordeum vulgare L.) and spinach (Spinacia oleracea L.). This limitation by phosphate was evidenced by (i) reversibility of the inhibition of photosynthesis by glycerol by feeding orthophosphate (ii) a decrease in light-saturated rates of photosynthesis and saturation at a lower irradiance, (iii) the promotion of oscillations in photosynthetic CO2 assimilation and in chlorophyll fluorescence, (iv) decreases in the pools of hexose monophosphates and triose phosphates and increases in the ratio of glycerate-3-phosphate to triose phosphate, (v) decreased photochemical quenching of chlorophyll fluorescence, and increased non-photochemical quenching, specifically of the component which relaxed rapidly, indicating that thylakoid energisation had increased. In barley there was a massive accumulation of glycerol-3-phosphate and an increase in the period of the oscillations, but in spinach the accumulation of glycerol-3-phosphate was comparatively slight. The mechanism(s) by which glycerol feeding affects photosynthetic carbon assimilation are discussed in the light of these results.Abbreviations Chl chlorophyll - C i intercellular concentration of CO2 - P phosphate - PGA glycerate-3-phosphate - Pi orthophosphate - triose-P sum of glyceraldehyde-3-phosphate and dihydroxyacetone phosphate  相似文献   

8.
Abutilon theophrasti (C3) and Amaranthus retroflexus (C4), were grown from seed at four partial pressures of CO2: 15 Pa (below Pleistocene minimum), 27 Pa (pre-industrial), 35 Pa (current), and 70 Pa (future) in the Duke Phytotron under high light, high nutrient, and wellwatered conditions to evaluate their photosynthetic response to historic and future levels of CO2. Net photosynthesis at growth CO2 partial pressures increased with increasing CO2 for C3 plants, but not C4 plants. Net photosynthesis of Abutilon at 15 Pa CO2 was 70% less than that of plants grown at 35 Pa CO2, due to greater stomatal and biochemical limitations at 15 Pa CO2. Relative stomatal limitation (RSL) of Abutilon at 15 Pa CO2 was nearly 3 times greater than at 35 Pa CO2. A photosynthesis model was used to estimate ribulose-1,5-bisphosphate carboxylase (rubisco) activity (Vcmax), electron transport mediated RuBP regeneration capacity (J max), and phosphate regeneration capacity (PiRC) in Abutilon from net photosynthesis versus intercellular CO2 (AC i) curves. All three component processes decreased by approximately 25% in Abutilon grown at 15 Pa compared with 35 Pa CO2. Abutilon grown at 15 Pa CO2 had significant reductions in total rubisco activity (25%), rubisco content (30%), activation state (29%), chlorophyll content (39%), N content (32%), and starch content (68%) compared with plants grown at 35 Pa CO2. Greater allocation to rubisco relative to light reaction components and concomitant decreases in J max and PiRC suggest co-regulation of biochemical processes occurred in Abutilon grown at 15 Pa CO2. There were no significant differences in photosynthesis or leaf properties in Abutilon grown at 27 Pa CO2 compared with 35 Pa CO2, suggesting that the rise in CO2 since the beginning of the industrial age has had little effect on the photosynthetic performance of Abutilon. For Amaranthus, limitations of photosynthesis were balanced between stomatal and biochemical factors such that net photosynthesis was similar in all CO2 treatments. Differences in photosynthetic response to growth over a wide range of CO2 partial pressures suggest changes in the relative performance of C3 and C4 annuals as atmospheric CO2 has fluctuated over geologic time.  相似文献   

9.
Tognetti  R.  Sebastiani  L.  Vitagliano  C.  Raschi  A.  Minnocci  A. 《Photosynthetica》2001,39(3):403-410
Five-year-old plants of two olive cultivars (Frantoio and Moraiolo) grown in large pots were exposed for 7 to 8 months to ambient (AC) or elevated (EC) CO2 concentration in a free-air CO2 enrichment (FACE) facility. Exposure to EC enhanced net photosynthetic rate (P N) and decreased stomatal conductance, leading to greater instantaneous transpiration efficiency. Stomata density also decreased under EC, while the ratio of intercellular (C i) to atmospheric CO2 concentration and chlorophyll content did not differ, except for the cv. Moraiolo after seven months of exposure to EC. Analysis of the relationship between photosynthesis and C i indicated no significant change in carboxylation efficiency of ribulose-1,5-bisphosphate carboxylase/oxygenase after five months of exposure to EC. Based on estimates derived from the P N-C i relationship, there were no apparent treatment differences in daytime respiration, CO2 compensation concentration, CO2-saturated photosynthetic rate, or photosynthetic rate at the mean C i, but there was a reduction in stomata limitation to P N at EC. Thus 5-year-old olive trees did not exhibit down regulation of leaf-level photosynthesis in their response to EC, though some indication of adjustment was evident for the cv. Frantoio with respect to the cv. Moraiolo.  相似文献   

10.
Restrictions to photosynthesis can limit plant growth at high temperature in a variety of ways. In addition to increasing photorespiration, moderately high temperatures (35–42 °C) can cause direct injury to the photosynthetic apparatus. Both carbon metabolism and thylakoid reactions have been suggested as the primary site of injury at these temperatures. In the present study this issue was addressed by first characterizing leaf temperature dynamics in Pima cotton (Gossypium barbadense) grown under irrigation in the US desert south‐west. It was found that cotton leaves repeatedly reached temperatures above 40 °C and could fluctuate as much as 8 or 10 °C in a matter of seconds. Laboratory studies revealed a maximum photosynthetic rate at 30–33 °C that declined by 22% at 45 °C. The majority of the inhibition persisted upon return to 30 °C. The mechanism of this limitation was assessed by measuring the response of photosynthesis to CO2 in the laboratory. The first time a cotton leaf (grown at 30 °C) was exposed to 45 °C, photosynthetic electron transport was stimulated (at high CO2) because of an increased flux through the photorespiratory pathway. However, upon cooling back to 30 °C, photosynthetic electron transport was inhibited and fell substantially below the level measured before the heat treatment. In the field, the response of assimilation (A) to various internal levels of CO2 (Ci) revealed that photosynthesis was limited by ribulose‐1,5‐bisphosphate (RuBP) regeneration at normal levels of CO2 (presumably because of limitations in thylakoid reactions needed to support RuBP regeneration). There was no evidence of a ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) limitation at air levels of CO2 and at no point on any of 30 ACi curves measured on leaves at temperatures from 28 to 39 °C was RuBP regeneration capacity measured to be in substantial excess of the capacity of Rubisco to use RuBP. It is therefore concluded that photosynthesis in field‐grown Pima cotton leaves is functionally limited by photosynthetic electron transport and RuBP regeneration capacity, not Rubisco activity.  相似文献   

11.
The photosynthetic characterization of the oriental lily (Lilium) cv. Sorbonne and its response to increasing water stress were analyzed based on the net photosynthetic rate (P n), stomatal conductance (g s), intercellular CO2 concentration (Ci), transpiration rate (E), water use efficiency (WUE), and stomatal limitation (Ls) in the Horqin Sandy Land of western China. A photosynthesis-PAR response curve was constructed to obtain light-compensation and light-saturation points (LCP and LSP), the maximum photosynthetic rates (P max) and dark respiration rates (R D). The growth of lilies in the pots was analyzed after anthesis. Various intensities of water stress (5, 10, and 20 days without water, and an unstressed control) were applied. The results indicated that drought stress not only significantly decreased P n, E, g s, photosynthetic pigment content (Chl a, Chl b, and Chl (a + b)) and increased intrinsic water use efficiency (WUE), but also altered the diurnal pattern of gas exchange. Drought stress also affected the photosynthesis (P n)-PAR response curve. Drought stress increased LCP and R D and decreased LSP and P max. There were both stomatal and nonstomatal limitations to photosynthesis. Stomatal limitation dominated in the morning, whereas nonstomatal limitation dominated in the afternoon. Thus, drought stress decreased potential photosynthetic capacity and affected the diurnal pattern of gas exchange and P n-PAR response curves, thereby reducing plant quality (lower plant height, flower length, flower diameter, and leaf area). Water stress is likely the main limitation to primary photosynthetic process in the lily. Appropriate watering is recommended to improve photosynthetic efficiency and alleviate photodamage, which will increase the commercial value of the lily in the Horqin Sandy Land.  相似文献   

12.
The nature of photosynthetic acclimation to elevated CO2 is evaluated from the results of over 40 studies focusing on the effect of long-term CO2 enrichment on the short-term response of photosynthesis to intercellular CO2 (the A/Ci response). The effect of CO2 enrichment on the A/Ci response was dependent on growth conditions, with plants grown in small pots (< 5 L) or low nutrients usually exhibiting a reduction of A at a given Ci, while plants grown without nutrient deficiency in large pots or in the field tended to exhibit either little reduction or an enhancement of A at a given Ci following a doubling or tripling of atmospheric CO2 during growth. Using theoretical interpretations of A/Ci curves to assess acclimation, it was found that when pot size or nutrient deficiency was not a factor, changes in the shape of A/Ci curves which are indicative of a reallocation of resources within the photosynthetic apparatus typically were not observed. Long-term CO2 enrichment usually had little effect or increased the value of A at all Ci. However, a minority of species grown at elevated CO2 exhibited gas exchange responses indicative of a reduced amount of Rubisco and an enhanced capacity to metabolize photosynthetic products. This type of response was considered beneficial because it enhanced both photosynthetic capacity at high CO2 and reduced resource investment in excessive Rubisco capacity. The ratio of intercellular to ambient CO2 (the Ci/Ca ratio) was used to evaluate stomatal acclimation. Except under water and humidity stress, Ci/Ca exhibited no consistent change in a variety of C3 species, indicating no stomatal acclimation. Under drought or humidity stress, Ci/Ca declined in high-CO2 grown plants, indicating stomata will become more conservative during stress episodes in future high CO2 environments.Abbreviations A net CO2 assimilation rate - Ci (Ca) intercellular (ambient) partial pressure of CO2 - operational Ci intercellular partial pressure of CO2 at a given ambient partial pressure of CO2 - gs stomatal conductance - normal CO2 current atmospheric mole fraction of CO2 (330 to 355 mol mol–1) - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase  相似文献   

13.
The levels of stomatal, mesophyll and biochemical limitations in CO2 assimilation of ‘Bluecrop’ highbush blueberry leaves were compared at two different levels of leaf water potential. The leaf water potentials were ?1.49 and ?1.94 MPa in daily-irrigated (DI) and non-irrigated (NI) shrubs, respectively. The NI shrubs represented plants under moderate water stress. Mesophyll conductance (g m) and chloroplastic CO2 concentration (C c) were estimated by combined measurements of gas exchange and chlorophyll fluorescence under various intercellular CO2 concentrations (C i). Net CO2 assimilation rates (A n) as a function of C c were used for calculating maximum carboxylation efficiency (α cmax) at the real sites of CO2 assimilation. Maximum A n (A nmax) from the light response curves at 400 μmol mol?1 air of ambient CO2 concentration (C a) were lower in the leaves of NI shrubs than in those of DI ones. However, electron transport rates were higher in the leaves of NI shrubs than in those of DI ones. The decrease in CO2 assimilation following water stress may be caused by a decrease in g m rather than a decrease in stomatal conductance (g s) according to limitation analysis. Limitation rates by g s, calculated at 400 μmol mol?1 air of C a in A n-C i curves, were not significantly different between the leaves of DI and NI shrubs. However, limitation rates by g m from A n-C c curves were significantly higher in the leaves of NI shrubs than in those of DI ones. Maximum carboxylation efficiency (α cmax) values calculated from the A n-C c curve, contrary to those calculated from the A n-C i curve, were higher in the leaves of NI shrubs than in those of DI ones. Consequently, mesophyll limitation than stomatal and biochemical limitations mainly down-regulated the photosynthesis in the leaves of ‘Bluecrop’ blueberry shrubs during moderate water stress.  相似文献   

14.
The effect of increased salinity on photosynthesis was studied in leaves of Plantago maritima L. that developed while plants were at low and high NaCl levels. In leaves that developed while plants were grown at 50 mol·m-3, exposure to 200 and 350 mol·m-3 NaCl resulted in reductions in net CO2 assimilation and stomatal conductance. The decline in CO2 assimilation in plants at 200 and 350 mol·m-3 NaCl occurred almost exclusively at high intercellular CO2 concentrations. The initial slope of the CO2 assimilation-intercellular CO2 (A-C i) curve, determined after salinity was increased, was identical or very similar to that measured initially. In contrast to the reductions observed in CO2 assimilation, there were no significant differences in O2 evolution rates measured at 5% CO2 among leaves from plants exposed to higher salinity and plants remaining at low salinity.Leaves that developed while plants were at increased salinity levels also had significantly lower net CO2 assimilation rates than plants remaining at 50 mol·m-3 NaCl. The lower CO2 assimilation rates in plants grown at 200 and 350 mol·m-3 NaCl were a result of reduced stomatal conductance and low intercellular CO2 concentration. There were no significant differences among treatments for O2 evolution rates measured at high CO2 levels. The increased stomatal limitation of photosynthesis was confirmed by measurements of the 13C/12C composition of leaf tissue. Water-use efficiency was increased in the plants grown at high salinity.Abbreviations and symbols A net CO2 assimilation rate - C a ambient CO2 concentration - C i intercellular CO2 concentration - 13C isotopic ratio (13C/12C) expressed relative to a standard - RuBP ribulose-1,5-bisphosphate  相似文献   

15.
Twin Cays (Belize) is a highly oligotrophic mangrove archipelago dominated by Rhizophora mangle L. Ocean‐fringing trees are 3–7 m tall with a leaf area index (LAI) of 2.3, whereas in the interior, dwarf zone, trees are 1.5 m or less, and the LAI is 0.7. P‐fertilization of dwarf trees dramatically increases growth. As a partial explanation of these characteristics, it was hypothesized that differences in stature and growth rates would reflect differences in leaf photosynthetic capacity, as determined by the photochemical and biochemical characteristics at the chloroplast level. Gas exchange and chlorophyll fluorescence were used to compare photosynthesis of dwarf, fringe and fertilized trees. Regardless of zonation or treatment, net CO2 exchange (A) and photosynthetic electron transport were light saturated at less than 500 µmol photons m?2 s?1, and low‐light quantum efficiencies were typical for healthy C3 plants. On the other hand, light‐saturated A was linearly related to stomatal conductance (gs), with seasonal, zonal and treatment differences in photosynthesis corresponding linearly to differences in the mean gs. Overall, photosynthetic capacity appeared to be co‐regulated with stomatal conductance, minimizing the variability of Ci at ambient CO2 (and hence, Ci/Ca). Based on the results of in vitro assays, regulation of photosynthesis in R. mangle appeared to be accomplished, at least in part, by regulation of Rubisco activity.  相似文献   

16.
X. Guan  S. Gu 《Photosynthetica》2009,47(3):437-444
In order to investigate the photoprotective function of photorespiration in grapevine under water stress, potted grapevines (Vitis vinifera L. cv. Cabernet Sauvignon) were randomly divided into three uniform groups for well-watered [watered every morning to keep the relative water content (RWC) of soil over 70 %], water-stress adapted (drought-adapted at 30 % relative soil water content for 30 days), and water stress without adaptation treatment (water-stressed to 30 % relative soil water content for 3 days). Net assimilation rate (A N), stomatal conductance (g s), substomatal CO2 concentration (C i), transpiration rate (E), actual photochemical efficiency of PSII (ΦPSII), and maximum photochemical efficiency of PSII (Fv/Fm) were recorded by combining measurements of gas exchange and chlorophyll fluorescence. Gross photorespiration (Pr), photosynthetic electron partitioning (JC/JT), photochemical quenching coefficient (qP), and non-photochemical quenching (NPQ) were also calculated. The ratio of net assimilation rate to transpiration rate (A N/E) was used as an indicator of water use efficiency (WUE). A N, apparent Pr, ΦPSII, Fv/Fm, qp, and g s decreased, NPQ increased, and gross Pr sustained at a high level under water stress. This suggests that both photorespiration and energy dissipation play important roles in protecting photosynthetic apparatus against photoinhibition. C i in water-stressed plants without adaptation treatment increased, which indicates the leaves suffered a non-stomatal limitation, while the water-stress adaped plants only suffered a stomatal limitation indicated by low C i.  相似文献   

17.
We have investigated the role of polyunsaturated fatty acids in photosynthesis using a triple mutant of Arabidopsis thaliana that lacks trienoic fatty acids (fad 3-2 fad 7-2 fad 8). Though this mutant is male sterile, vegetative growth and development under normal conditions are largely unaffected (McConn and Browse, 1996 Plant Cell 8: 403–416). At 0.2–1.0 kPa vapor pressure deficit (low VPD), maximum photosynthetic rates of wild-type and mutant plants were similar while stomatal conductance rates were up to 2 times higher in mutant plants. However, light-saturated rates of carbon assimilation and stomatal conductance in the mutant were lower than in wild-type plants when measured at ambient (35 Pa) CO2 and 2.0–2.8 kPa vapor pressure deficit (high VPD). The limitation to photosynthesis in the mutant plants at high VPD was overcome by saturating partial pressures of CO2 suggesting a stomatal limitation. Chlorophyll fluorescence measurements indicate that differences observed in maximum assimilation rates were not due to limitations within the photochemical reactions of photosynthesis. Stomatal response to VPD and intrinsic water use efficiency was drastically different in mutant versus wild-type plants. The results of this investigation indicate that for Arabidopsis, polyunsaturated fatty acids may be an important determinant of responses of photosynthesis and stomatal conductance to environmental stresses such as high VPD. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

18.
Thomas Graan  John S. Boyer 《Planta》1990,181(3):378-384
We re-examined the question of whether the stomata limit photosynthesis in dehydrated sunflower (Helianthus annuus L.) plants having low leaf water potentials. A gas-exchange apparatus was modified to operate at external CO2 partial pressures as high as 3000 Pa (3%), which were much higher than previously achieved. This allowed photosynthesis and stomatal behavior to be monitored simultaneously at very high CO2 in the same leaf. The data were compared with those from leaves treated with abscisic acid (ABA) where effects on photosynthesis are entirely stomatal. Photosynthesis was inhibited at low water potential and was only slightly enhanced by increasing the external CO2 partial pressure from 34 Pa (normal air) to 300 Pa. Photosynthesis in ABA-treated leaves was similarly inhibited but recovered fully at 300 Pa. In both cases, the stomata closed to the same extent as judged from the average conductance of the leaves. Because the ABA effect resulted from diffusion limitation for CO2 caused by stomatal closure, the contrasting data show that most of the dehydration effect was nonstomatal at low water potentials. When CO2 partial pressures were raised further to 3000 Pa, photosynthesis increased somewhat at low water potentials but not in ABA-treated leaves. This indicates that some nonstomatal component of photosynthesis responded differently in leaves at low water potential and leaves treated with ABA. Because this component was only partially restored by very high CO2, it was likely to be metabolic and was an important source of photosynthetic inhibition.Abbreviations and Symbol ABA abscisic acid - Chl chlorophyll - pa external partial pressure of CO2 - Pi intercellular partial pressure of CO2 - w water potential This work was supported by grant DE-FG02-87ER13776 from the Department of Energy and a grant from E.I. DuPont de Nemours and Company.  相似文献   

19.
C4 photosynthesis and water stress   总被引:1,自引:0,他引:1  
Ghannoum O 《Annals of botany》2009,103(4):635-644

Background

In contrast to C3 photosynthesis, the response of C4 photosynthesis to water stress has been less-well studied in spite of the significant contribution of C4 plants to the global carbon budget and food security. The key feature of C4 photosynthesis is the operation of a CO2-concentrating mechanism in the leaves, which serves to saturate photosynthesis and suppress photorespiration in normal air. This article reviews the current state of understanding about the response of C4 photosynthesis to water stress, including the interaction with elevated CO2 concentration. Major gaps in our knowledge in this area are identified and further required research is suggested.

Scope

Evidence indicates that C4 photosynthesis is highly sensitive to water stress. With declining leaf water status, CO2 assimilation rate and stomatal conductance decrease rapidly and photosynthesis goes through three successive phases. The initial, mainly stomatal phase, may or may not be detected as a decline in assimilation rates depending on environmental conditions. This is because the CO2-concentrating mechanism is capable of saturating C4 photosynthesis under relatively low intercellular CO2 concentrations. In addition, photorespired CO2 is likely to be refixed before escaping the bundle sheath. This is followed by a mixed stomatal and non-stomatal phase and, finally, a mainly non-stomatal phase. The main non-stomatal factors include reduced activity of photosynthetic enzymes; inhibition of nitrate assimilation, induction of early senescence, and changes to the leaf anatomy and ultrastructure. Results from the literature about CO2 enrichment indicate that when C4 plants experience drought in their natural environment, elevated CO2 concentration alleviates the effect of water stress on plant productivity indirectly via improved soil moisture and plant water status as a result of decreased stomatal conductance and reduced leaf transpiration.

Conclusions

It is suggested that there is a limited capacity for photorespiration or the Mehler reaction to act as significant alternative electron sinks under water stress in C4 photosynthesis. This may explain why C4 photosynthesis is equally or even more sensitive to water stress than its C3 counterpart in spite of the greater capacity and water use efficiency of the C4 photosynthetic pathway.Key words: C3 and C4 photosynthesis, stomatal and non-stomatal limitation, high CO2, water stress  相似文献   

20.
The photosynthetic response of Larrea tridentata Cav., an evergreen Mojave Desert shrub, to elevated atmospheric CO2 and drought was examined to assist in the understanding of how plants from water-limited ecosystems will respond to rising CO2. We hypothesized that photosynthetic down-regulation would disappear during periods of water limitation, and would, therefore, likely be a seasonally transient event. To test this we measured photosynthetic, water relations and fluorescence responses during periods of increased and decreased water availability in two different treatment implementations: (1) from seedlings exposed to 360, 550, and 700 μmol mol–1 CO2 in a glasshouse; and (2) from intact adults exposed to 360 and 550 μmol mol–1 CO2 at the Nevada Desert FACE (Free Air CO2 Enrichment) Facility. FACE and glasshouse well-watered Larrea significantly down-regulated photosynthesis at elevated CO2, reducing maximum photosynthetic rate (Amax), carboxylation efficiency (CE), and Rubisco catalytic sites, whereas droughted Larrea showed a differing response depending on treatment technique. Amax and CE were lower in droughted Larrea compared with well-watered plants, and CO2 had no effect on these reduced photosynthetic parameters. However, Rubisco catalytic sites decreased in droughted Larrea at elevated CO2. Operating Ci increased at elevated CO2 in droughted plants, resulting in greater photosynthetic rates at elevated CO2 as compared with ambient CO2. In well-watered plants, the changes in operating Ci, CE and Amax resulted in similar photosynthetic rates across CO2 treatments. Our results suggest that drought can diminish photosynthetic down-regulation to elevated CO2 in Larrea, resulting in seasonally transient patterns of enhanced carbon gain. These results suggest that water status may ultimately control the photosynthetic response of desert systems to rising CO2.  相似文献   

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