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1.
The effects of atmospheric CO 2 enrichment and root restriction on photosynthetic characteristics and growth of banana ( Musa sp. AAA cv. Gros Michel) plants were investigated. Plants were grown aeroponically in root chambers in controlled environment glasshouse rooms at CO 2 concentrations of 350 or 1 000 μmol CO 2 mol -1. At each CO 2 concentration, plants were grown in large (2001) root chambers that did not restrict root growth or in small (20 1) root chambers that restricted root growth. Plants grown at 350 μmol CO 2 mol -1 generally had a higher carboxylation efficiency than plants grown at 1 000 μmol CO 2 mol -1 although actual net CO 2 assimilation ( A) was higher at the higher ambient CO 2 concentration due to increased intercellular CO 2 concentrations ( Ci resulting from CO 2 enrichment. Thus, plants grown at 1 000 μmol CO 2 mol -1 accumulated more leaf area and dry weight than plants grown at 350 μmol CO 2 mol -1. Plants grown in the large root chambers were more photosynthetically efficient than plants grown in the small root chambers. At 350 μmol CO 2 mol -1, leaf area and dry weights of plant organs were generally greater for plants in the large root chambers compared to those in the small root chambers. Atmospheric CO 2 enrichment may have compensated for the effects of root restriction on plant growth since at 1 000 μmol CO 2 mol -1 there was generally no effect of root chamber size on plant dry weight. 相似文献
2.
Upland rice ( Oryza sativa L.) was grown at both ambient (350 μmol mol ?1) and elevated (700 μmol mol ?1) CO 2 in either the presence or absence of the root hemi‐parasitic angiosperm Striga hermonthica (Del) Benth. Elevated CO 2 alleviated the impact of the parasite on host growth: biomass of infected rice grown at ambient CO 2 was 35% that of uninfected, control plants, while at elevated CO 2, biomass of infected plants was 73% that of controls. This amelioration occurred despite the fact that O. sativa grown at elevated CO 2 supported both greater numbers and a higher biomass of parasites per host than plants grown at ambient CO 2. The impact of infection on host leaf area, leaf mass, root mass and reproductive tissue mass was significantly lower in plants grown at elevated as compared with ambient CO 2. There were significant CO 2 and Striga effects on photosynthetic metabolism and instantaneous water‐use efficiency of O. sativa. The response of photosynthesis to internal [CO 2] ( A/ Ci curves) indicated that, at 45 days after sowing (DAS), prior to emergence of the parasites, uninfected plants grown at elevated CO 2 had significantly lower CO 2 saturated rates of photosynthesis, carboxylation efficiencies and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) contents than uninfected, ambient CO 2‐grown O. sativa. In contrast, infection with S. hermonthica prevented down‐regulation of photosynthesis in O. sativa grown at elevated CO 2, but had no impact on photosynthesis of hosts grown at ambient CO 2. At 76 DAS (after parasites had emerged), however, infected plants grown at both elevated and ambient CO 2 had lower carboxylation efficiencies and Rubisco contents than uninfected O. sativa grown at ambient CO 2. The reductions in carboxylation efficiency (and Rubisco content) were accompanied by similar reductions in nitrogen concentration of O. sativa leaves, both before and after parasite emergence. There were no significant CO 2 or infection effects on the concentrations of soluble sugars in leaves of O. sativa, but starch concentration was significantly lower in infected plants at both CO 2 concentrations. These results demonstrate that elevated CO 2 concentrations can alleviate the impact of infection with Striga on the growth of C 3 hosts such as rice and also that infection can delay the onset of photosynthetic down‐regulation in rice grown at elevated CO 2. 相似文献
3.
Nutrients such as phosphorus may exert a major control over plant response to rising atmospheric carbon dioxide concentration (CO 2), which is projected to double by the end of the 21st century. Elevated CO 2 may overcome the diffusional limitations to photosynthesis posed by stomata and mesophyll and alter the photo-biochemical limitations resulting from phosphorus deficiency. To evaluate these ideas, cotton ( Gossypium hirsutum) was grown in controlled environment growth chambers with three levels of phosphate (Pi) supply (0.2, 0.05 and 0.01 mM) and two levels of CO 2 concentration (ambient 400 and elevated 800 μmol mol −1) under optimum temperature and irrigation. Phosphate deficiency drastically inhibited photosynthetic characteristics and decreased cotton growth for both CO 2 treatments. Under Pi stress, an apparent limitation to the photosynthetic potential was evident by CO 2 diffusion through stomata and mesophyll, impairment of photosystem functioning and inhibition of biochemical process including the carboxylation efficiency of ribulose-1,5-bisphosphate carboxylase/oxyganase and the rate of ribulose-1,5-bisphosphate regeneration. The diffusional limitation posed by mesophyll was up to 58% greater than the limitation due to stomatal conductance ( gs) under Pi stress. As expected, elevated CO 2 reduced these diffusional limitations to photosynthesis across Pi levels; however, it failed to reduce the photo-biochemical limitations to photosynthesis in phosphorus deficient plants. Acclimation/down regulation of photosynthetic capacity was evident under elevated CO 2 across Pi treatments. Despite a decrease in phosphorus, nitrogen and chlorophyll concentrations in leaf tissue and reduced stomatal conductance at elevated CO 2, the rate of photosynthesis per unit leaf area when measured at the growth CO 2 concentration tended to be higher for all except the lowest Pi treatment. Nevertheless, plant biomass increased at elevated CO 2 across Pi nutrition with taller plants, increased leaf number and larger leaf area. 相似文献
4.
Two cultivars of rice ( Oryza sativa L.) IR-36 and Fujiyama-5 were grown at ambient (360 microbars) and elevated CO 2 (660 microbars) from germination through reproduction in unshaded greenhouses at the Duke University Phytotron. Growth at elevated CO 2 resulted in significant decreases in nighttime respiration and increases in photosynthesis, total biomass, and yield for both cultivars. However, in plants exposed to simultaneous increases in CO 2 and ultraviolet-B (UV-B) radiation, CO 2 enhancement effects on respiration, photosynthesis, and biomass were eliminated in IR-36 and significantly reduced in Fujiyama-5. UV-B radiation simulated a 25% depletion in stratospheric ozone at Durham, North Carolina. Analysis of the response of CO 2 uptake to internal CO 2 concentration at light saturation suggested that, for IR-36, the predominant limitation to photosynthesis with increased UV-B radiation was the capacity for regeneration of ribulose bisphosphate (RuBP), whereas for Fujiyama-5 the primary photosynthetic decrease appeared to be related to a decline in apparent carboxylation efficiency. Changes in the RuBP regeneration limitation in IR-36 were consistent with damage to the photochemical efficiency of photosystem II as estimated from the ratio of variable to maximum chlorophyll fluorescence. Little change in RuBP regeneration and photochemistry was evident in cultivar Fujiyama-5, however. The degree of sensitivity of photochemical reactions with increased UV-B radiation appeared to be related to leaf production of UV-B-absorbing compounds. Fujiyama-5 had a higher concentration of these compounds than IR-36 in all environments, and the production of these compounds in Fujiyama-5 was stimulated by UV-B fluence. Results from this study suggest that in rice alterations in growth or photosynthesis as a result of enhanced CO 2 may be eliminated or reduced if UV-B radiation continues to increase. 相似文献
5.
Previous studies of photosynthetic acclimation to elevated CO 2 have focused on the most recently expanded, sunlit leaves in the canopy. We examined acclimation in a vertical profile of leaves through a canopy of wheat ( Triticum aestivum L.). The crop was grown at an elevated CO 2 partial pressure of 55 Pa within a replicated field experiment using free-air CO 2 enrichment. Gas exchange was used to estimate in vivo carboxylation capacity and the maximum rate of ribulose-1,5-bisphosphate-limited photosynthesis. Net photosynthetic CO 2 uptake was measured for leaves in situ within the canopy. Leaf contents of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), light-harvesting-complex (LHC) proteins, and total N were determined. Elevated CO 2 did not affect carboxylation capacity in the most recently expanded leaves but led to a decrease in lower, shaded leaves during grain development. Despite this acclimation, in situ photosynthetic CO 2 uptake remained higher under elevated CO 2. Acclimation at elevated CO 2 was accompanied by decreases in both Rubisco and total leaf N contents and an increase in LHC content. Elevated CO 2 led to a larger increase in LHC/Rubisco in lower canopy leaves than in the uppermost leaf. Acclimation of leaf photosynthesis to elevated CO 2 therefore depended on both vertical position within the canopy and the developmental stage. 相似文献
6.
Winter wheat ( Triticum aestivum L., cv. Mercia) was grown at two different atmospheric CO 2 concentrations (350 and 700 μmol mol −1), two temperatures [ambient temperature (i.e. tracking the open air) and ambient +4°C] and two rates of nitrogen supply (equivalent to 489 kg ha −1 and 87 kg ha −1). Leaves grown at 700 μmol mol −1 CO 2 had slightly greater photosynthetic capacity (10% mean increase over the experiment) than those grown at ambient CO 2 concentration, but there were no differences in carboxylation efficiency or apparent quantum yield. The amounts of chlorophyll, soluble protein and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) per unit leaf area did not change with long-term exposure to elevated CO 2 concentration. Thus winter wheat, grown under simulated field conditions, for which total biomass was large compared to normal field production, did not experience loss of components of the photosynthetic system or loss of photosynthetic competence with elevated CO 2 concentration. However, nitrogen supply and temperature had large effects on photosynthetic characteristics but did not interact with elevated CO 2 concentration. Nitrogen deficiency resulted in decreases in the contents of protein, including Rubisco, and chlorophyll, and decreased photosynthetic capacity and carboxylation efficiency. An increase in temperature also reduced these components and shortened the effective life of the leaves, reducing the duration of high photosynthetic capacity. 相似文献
7.
The physiological characteristics of holm oak ( Quercus ilex L.) resprouts originated from plants grown under current CO 2 concentration (350 μl l −1) (A-resprouts) were compared with those of resprouts originated from plants grown under elevated CO 2 (750 μl l −1) (E-resprouts). At their respective CO 2 growth concentration, no differences were observed in photosynthesis and chlorophyll fluorescence parameters between the two kinds of resprout. E-resprouts appeared earlier and showed lower stomatal conductance, higher water-use efficiency and increased growth (higher leaf, stem and root biomass and increased height). Analyses of leaf chemical composition showed the effect of elevated [CO 2] on structural polysaccharide (higher cellulose content), but no accumulation of total non-structural carbohydrate on area or dry weight basis was seen. Four months after appearance, downregulation of photosynthesis and electron transport components was observed in E-resprouts: lower photosynthetic capacity, photosystem II quantum efficiency, photochemical quenching of fluorescence and relative electron transport rate. Reduction in ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo) activity, deduced from the maximum carboxylation velocity of RuBisCo, accounts for the observed acclimation. Increased susceptibility of photosynthetic apparatus to increasing irradiance was detected in E-resprouts. 相似文献
8.
Midday measurements of single leaf gas exchange rates of upper canopy leaves of soybeans grown in the field at 350 (AC) and 700 (EC) µmol(CO 2) mol –1 in open topped chambers sometimes indicated up to 50 % higher net photosynthetic rates ( P
N) measured at EC in plants grown at AC compared to EC. On other days mean P
N were nearly identical in the two growth [CO 2] treatments. There was no seasonal pattern to the variable photosynthetic responses of soybean to growth [CO 2]. Even on days with significantly lower P
N in the plants grown at EC, there was no reduction in ribulose-1,5-bisphosphate carboxylase/oxygenase, chlorophyll, or soluble protein contents per unit of leaf area. Over three years, gas exchange evidence of acclimation occurred on days when either soil was dry or the water vapor pressure deficit was high ( n = 12 d) and did not occur on days after rain or on days with low water vapor pressure deficit ( n = 9 d). On days when photosynthetic acclimation was evident, midday leaf water potentials were consistently 0.2 to 0.3 MPa lower for the plants grown at EC than at AC. This suggested that greater susceptibility to water stress in plants grown at EC cause the apparent photosynthetic acclimation. In other experiments, plants were grown in well-watered pots in field chambers and removed to the laboratory early in the morning for gas exchange measurements. In these experiments, the amount of photosynthetic acclimation evident in the gas exchange measurements increased with the maximum water vapor pressure deficit on the day prior to the measurements, indicating a lag in the recovery of photosynthesis from water stress. The apparent increase in susceptibility to water stress in soybean plants grown at EC is opposite to that observed in some other species, where photosynthetic acclimation was evident under wet but not dry conditions, and may be related to the observation that hydraulic conductance is reduced in soybeans when grown at EC. The day-to-day variation in photosynthetic acclimation observed here may account for some of the conflicting results in the literature concerning the existence of acclimation to EC in field-grown plants. 相似文献
9.
Analysis of leaf-level photosynthetic responses of 39 tree species grown in elevated concentrations of atmospheric CO 2 indicated an average photosynthetic enhancement of 44% when measured at the growth [CO 2]. When photosynthesis was measured at a common ambient [CO 2], photosynthesis of plants grown at elevated [CO 2] was reduced, on average, 21% relative to ambient-grown trees, but variability was high. The evidence linking photosynthetic acclimation in trees with changes at the biochemical level is examined, along with anatomical and morphological changes in trees that impact leaf- and canopy-level photosynthetic response to CO 2 enrichment. Nutrient limitations and variations in sink strength appear to influence photosynthetic acclimation, but the evidence in trees for one predominant factor controlling acclimation is lacking. Regardless of the mechanisms that underlie photosynthetic acclimation, it is doubtful that this response will be complete. A new focus on adjustments to rising [CO 2] at canopy, stand, and forest scales is needed to predict ecosystem response to a changing environment.Abbreviations A/C i
photosynthesis as a function of internal [CO 2]
- J max
maximum rate of electron transport
- Rubisco
ribulose-1,5-bisphosphate carboxylase/oxygenase
- Vc max
maximum rate of carboxylation
The U.S. Government right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged. 相似文献
10.
The effect of long-term (weeks to months) CO 2 enhancement on (a) the gas-exchange characteristics, (b) the content and activation state of ribulose-1,5-bisphosphate carboxylase (rubisco), and (c) leaf nitrogen, chlorophyll, and dry weight per area were studied in five C 3 species ( Chenopodium album, Phaseolus vulgaris, Solanum tuberosum, Solanum melongena, and Brassica oleracea) grown at CO 2 partial pressures of 300 or 900 to 1000 microbars. Long-term exposure to elevated CO 2 affected the CO 2 response of photosynthesis in one of three ways: (a) the initial slope of the CO 2 response was unaffected, but the photosynthetic rate at high CO 2 increased ( S. tuberosum); (b) the initial slope decreased but the CO 2-saturated rate of photosynthesis was little affected ( C. album, P. vulgaris); (c) both the initial slope and the CO 2-saturated rate of photosynthesis decreased ( B. oleracea, S. melongena). In all five species, growth at high CO 2 increased the extent to which photosynthesis was stimulated following a decrease in the partial pressure of O 2 or an increase in measurement CO 2 above 600 microbars. This stimulation indicates that a limitation on photosynthesis by the capacity to regenerate orthophosphate was reduced or absent after acclimation to high CO 2. Leaf nitrogen per area either increased ( S. tuberosum, S. melongena) or was little changed by CO 2 enhancement. The content of rubisco was lower in only two of the five species, yet its activation state was 19% to 48% lower in all five species following long-term exposure to high CO 2. These results indicate that during growth in CO 2-enriched air, leaf rubisco content remains in excess of that required to support the observed photosynthetic rates. 相似文献
11.
Controlled environment chamber and glasshouse studies were conducted on six herbaceous annual species grown at 350 (AC) and 700 (EC) mol(CO 2) mol -1 to determine whether growth at EC resulted in acclimation of the apparent quantum yield of photosynthesis (QY) measured at limiting photosynthetic photon flux density (PPFD), or in acclimation of net photosynthetic rate ( P
N) measured at saturating PPFD. It was also determined whether acclimation in P
N at limiting PPFD was correlated with acclimation of carboxylation efficiency or ribulose-1,5-bisphosphate (RuBP) regeneration rate measured at saturating PPFD. Growth at EC reduced both the QY and P
N at limiting PPFD in three of the six species. The occurrence of photosynthetic acclimation measured at a rate limiting PPFD was independent of whether photosynthetic acclimation was apparent at saturating measurement PPFD. At saturating measurement PPFD, acclimation to EC in the apparent carboxylation efficiency and RuBP regeneration capacity also occurred independently. Thus at least three components of the photosynthetic system may adjust independently when leaves are grown at EC. Estimates of photosynthetic acclimation at both high and low PPFD are necessary to accurately predict photosynthesis at the whole plant or canopy level as [CO 2] increases. 相似文献
12.
The effects of elevated CO 2 concentrations on the photochemistry, biochemistry and physiology of C 4 photosynthesis were studied in maize ( Zea mays L.). Plants were grown at ambient (350 μL L −1) or ca. 3 times ambient (1100 μL L −1) CO 2 levels under high light conditions in a greenhouse for 30 d. Relative to plants grown at ambient CO 2 levels, plants grown under elevated CO 2 accumulated ca. 20% more biomass and 23% more leaf area. When measured at the CO 2 concentration of growth, mature leaves of high-CO 2-grown plants had higher light-saturated rates of photosynthesis (ca. 15%), lower stomatal conductance (71%), higher water-use
efficiency (225%) and higher dark respiration rates (100%). High-CO 2-grown plants had lower carboxylation efficiencies (23%), measured under limiting CO 2, and lower leaf protein contents (22%). Activities of a number of C 3 and C 4 cycle enzymes decreased on a leaf-area basis in the high-CO 2-grown plants by 5–30%, with NADP-malate dehydrogenase exhibiting the greatest decrease. In contrast, activities of fructose
1,6-bisphosphatase and ADP-glucose pyrophosphorylase increased significantly under elevated CO 2 condition (8% and 36%, respectively). These data show that the C 4 plant maize may benefit from elevated CO 2 through acclimation in the capacities of certain photosynthetic enzymes. The increased capacity to synthesize sucrose and
starch, and to utilize these end-products of photosynthesis to produce extra energy by respiration, may contribute to the
enhanced growth of maize under elevated CO 2.
Received: 30 April 1999 / Accepted: 17 June 1999 相似文献
13.
Carbon uptake by forests constitutes half of the planet’s terrestrial net primary production; therefore, photosynthetic responses
of trees to rising atmospheric CO 2 are critical to understanding the future global carbon cycle. At the Swiss Canopy Crane, we investigated gas exchange characteristics
and leaf traits in five deciduous tree species during their eighth growing season under free air carbon dioxide enrichment
in a 35-m tall, ca. 100-year-old mixed forest. Net photosynthesis of upper-canopy foliage was 48% (July) and 42% (September)
higher in CO 2-enriched trees and showed no sign of down-regulation. Elevated CO 2 had no effect on carboxylation efficiency ( V
cmax) or maximal electron transport ( J
max) driving ribulose-1,5-bisphosphate (RuBP) regeneration. CO 2 enrichment improved nitrogen use efficiency, but did not affect leaf nitrogen (N) concentration, leaf thickness or specific
leaf area except for one species. Non-structural carbohydrates accumulated more strongly in leaves grown under elevated CO 2 (largely driven by Quercus). Because leaf area index did not change, the CO 2-driven stimulation of photosynthesis in these trees may persist in the upper canopy under future atmospheric CO 2 concentrations without reductions in photosynthetic capacity. However, given the lack of growth stimulation, the fate of
the additionally assimilated carbon remains uncertain. 相似文献
14.
Effects of irradiance on photosynthetic characteristics were examined in senescent leaves of rice ( Oryza sativa L.). Two irradiance treatments (100 and 20% natural sunlight) were imposed after the full expansion of the 13th leaf through senescence. The photosynthetic rate was measured as a function of intercellular CO 2 pressure with a gas-exchange system. The amounts of cytochrome f, coupling factor 1, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), and chlorophyll were determined. The coupling factor 1 and cytochrome f contents decreased rapidly during senescence, and their rates of decrease were much faster from the 20% sunlight treatment than from the full sunlight treatment. These changes were well correlated with those in the photosynthetic rate at CO 2 pressure = 600 microbars, but not with those under the ambient air condition (350 microbars CO 2) and 200 microbars CO 2. This suggested that the amounts of coupling factor 1 and cytochrome f from the full sunlight treatment cannot be limiting factors for the photosynthetic rate at ambient air conditions. The Rubisco content also decreased during senescence, but its decrease from the 20% sunlight treatment was appreciably retarded. However, this difference was not reflected in the photosynthetic rates at the ambient and 200 microbars CO 2. This implied that in vivo Rubisco activity may be regulated in the senescent leaves from the 20% sunlight treatment. The chlorophyll content decreased most slowly. In the 20% sunlight treatment, it remained apparently constant with a decline in chlorophyll a/b ratio. These photosynthetic characteristics of the senescent rice leaves under low irradiance were discussed in relation to acclimation of shade plants. 相似文献
15.
Summary The growth and photosynethetic responses to atmospheric CO 2 enrichment of 4 species of C 4 grasses grown at two levels of irradiance were studied. We sought to determine whether CO 2 enrichment would yield proportionally greater growth enhancement in the C 4 grasses when they were grown at low irradiance than when grown at high irradiance. The species studied were Echinochloa crusgalli, Digitaria sanguinalis, Eleusine indica, and Setaria faberi. Plants were grown in controlled environment chambers at 350, 675 and 1,000 l 1 -1 CO 2 and 1,000 or 150 mol m -2 s -1 photosynthetic photon flux density (PPFD). An increase in CO 2 concentration and PPFD significantly affected net photosynthesis and total biomass production of all plants. Plants grown at low PPFD had significantly lower rates of photosynthesis, produced less biomass, and had reduced responses to increases in CO 2. Plants grown in CO 2-enriched atmosphere had lower photosynthetic capacity relative to the low CO 2 grown plants when exposed to lower CO 2 concentration at the time of measurement, but had greater rate of photosynthesis when exposed to increasing PPFD. The light level under which the plants were growing did not influence the CO 2 compensation point for photosynthesis. 相似文献
16.
Cotton ( Gossypium hirsutum L. cv Stoneville 213) was grown at 350 and 1000 microliters per liter CO 2. The plants grown at elevated CO 2 concentrations contained large starch pools and showed initial symptoms of visible physical damage. Photosynthetic rates were lower than expected based on instantaneous exposure to high CO 2. A group of plants grown at 1000 microliters per liter CO2 was switched to 350 microliters per liter CO2. Starch pools and photosynthetic rates were monitored in the switched plants and in the two unswitched control groups. Photosynthetic rates per unit leaf area recovered to the level of the 350 microliters per liter CO2 grown control group within four to five days. To assess only nonstomatal limitations to photosynthesis, a measure of photosynthetic efficiencies was calculated (moles CO2 fixed per square meter per second per mole intercellular CO2). Photosynthetic efficiency also recovered to the levels of the 350 microliters per liter CO2 grown controls within three to four days. Recovery was correlated to a rapid depletion of the starch pool, indicating that the inhibition of photosynthesis is primarily a result of feedback inhibition. However, complete recovery may involve the repair of damage to the chloroplasts caused by excessive starch accumulation. The rapid and complete reversal of photosynthetic inhibition suggests that the appearance of large, strong sinks at certain developmental stages could result in reduction of the large starch accumulations and that photosynthetic rates could recover to near the theoretical capacity during periods of high photosynthate demand. 相似文献
17.
The future environment will exhibit increases in soil salt concentrations and atmospheric CO 2. In general, plant growth is inhibited by salt stress and stimulated by elevated CO 2. This study investigated whether elevated CO 2 could improve plant growth under salt stress and the mechanisms involved. We measured functional and morphological components of growth in barley (cv. Iranis) subjected to 0, 80, 160, or 240 mM NaCl and grown at either 350 (ambient) or 700 (elevated) μmol mol ?1 CO 2. Under nonsaline conditions, elevated CO 2 stimulated growth by increasing the relative growth rate (RGR). Maximum CO 2 stimulation was observed within the first 10 days of development, before the start of the salt treatment. Afterwards, salt stress caused reductions in biomass production and RGR by decreasing the photosynthetic rate and increasing the respiration rate; this resulted in a reduced net assimilation rate (functional component). In addition, salt stress caused nutritional imbalances, which reduced the leaf expansion capacity, and changed the root-to-shoot ratio. This resulted in reductions in the specific leaf area and leaf weight ratio (morphological components). However, the functional component became more relevant with increasing salt stress. Under elevated CO 2 conditions, salt stress inhibited growth less than that observed at ambient CO 2. This occurred because (1) more dry biomass was synthesized for a given leaf area due to higher photosynthetic rates, and (2) greater leaf area and root biomass were maintained for photosynthesis and water and mineral uptake, respectively. 相似文献
18.
Continually rising atmospheric CO 2 concentrations and possible climatic change may cause significant changes in plant communities. This study was undertaken to investigate gas exchange in two important grass species of the short-grass steppe, Pascopyrum smithii (western wheat-grass), C 3, and Bouteloua gracilis (blue grama), C4, grown at different CO 2 concentrations and temperatures. Intact soil cores containing each species were extracted from grasslands in north-eastern Colorado, USA, placed in growth chambers, and grown at combinations of two CO 2 concentrations (350 and 700 μmol mol −1) and two temperature regimes (field average and elevated by 4°C). Leaf gas exchange was measured during the second, third and fourth growth seasons. All plants exhibited higher leaf CO 2 assimilation rates ( A) with increasing measurement CO 2 concentration, with greater responses being observed in the cool-season C 3 species P. smithii. Changes in the shape of intercellular CO 2 response curves of A for both species indicated photosynthetic acclimation to the different growth environments. The photosynthetic capacity of P. smithii leaves tended to be reduced in plants grown at high CO 2 concentrations, although A for plants grown and measured at 700μmol mol −1 CO 2 was 41% greater than that in plants grown and measured at 350 μmol mol −1 CO 2. Low leaf N concentration may have contributed to photosynthetic acclimation to CO 2. A severe reduction in photosynthetic capacity was exhibited in P. smithii plants grown long-term at elevated temperatures. As a result, the potential response of photosynthesis to CO 2 enrichment was reduced in P. smithii plants grown long-term at the higher temperature. 相似文献
19.
Abstract. Plantago maritima L. was grown at three levels of salinity, 50, 200, 350 mol m −3 NaCl, and the effects on growth, ion content and photosynthetic capacity were studied. Shoot and root dry weight, leaf production and leaf length were all substantially reduced in plants grown at high salinity. Total leaf area of plants grown at 350 mol m −3 NaCl was only 20% of that in plants at low salinity. Both the Na + and K + content of leaves and roots increased with external salinity. There was no change in the Na +/K + ratio of leaves or roots at different salinity levels. Despite the large reductions in growth and high accumulation of Na + ions, leaf photosynthetic rate was only slightly reduced by salinity stress. The reduction in photosynthesis was not caused by reduced biochemical capacity as judged by photosynthetic response to intercellular CO 2 and by ribulose-1,5-bisphosphate carboxylase activity, but was due to reduced leaf conductance and low intercellular CO 2 concentration. The increased stomatal limitation of photosynthesis resulted in higher water-use efficiency of plants grown at high salinity. 相似文献
20.
Abstract. While photosynthesis of C 3 plants is stimulated by an increase in the atmospheric CO 2 concentration, photosynthetic capacity is often reduced after long-term exposure to elevated CO 2. This reduction appears to be brought about by end product inhibition, resulting from an imbalance in the supply and demand of carbohydrates. A review of the literature revealed that the reduction of photosynthetic capacity in elevated CO 2 was most pronounced when the increased supply of carbohydrates was combined with small sink size. The volume of pots in which plants were grown affected the sink size by restricting root growth. While plants grown in small pots had a reduced photosynthetic capacity, plants grown in the field showed no reduction or an increase in this capacity. Pot volume also determined the effect of elevated CO 2 on the root/shoot ratio: the root/shoot ratio increased when root growth was not restricted and decreased in plants grown in small pots. The data presented in this paper suggest that plants growing in the field will maintain a high photosynthetic capacity as the atmospheric CO 2 level continues to rise. 相似文献
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