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1.
Rates of CO 2 assimilation and leaf conductances to CO 2 transfer were measured in plants of Zea mays during a period of 14 days in which the plants were not rewatered, and leaf water potential decreased from −0.5 to −8.0 bar. At any given ambient partial pressure of CO 2, water stress reduced rate of assimilation and leaf conductance similarly, so that intercellular partial pressure of CO 2 remained almost constant. At normal ambient partial pressure of CO 2, the intercellular partial pressure of CO 2 was estimated to be 95 microbars. This is the same as had been estimated in plants of Zea mays grown with various levels of nitrogen supply, phosphate supply and irradiance, and in plants of Zea mays examined at different irradiances. After leaves of Phaseolus vulgaris L. and Eucalyptus pauciflora Sieb. ex Spreng had been exposed to high irradiance in an atmosphere of CO2-free N2 with 10 millibars O2, rates of assimilation and leaf conductances measured in standard conditions had decreased in similar proportions, so that intercellular partial pressure of CO2 remained almost unchanged. As the conductance of each epidermis that had not been directly irradiated had declined as much as that in the opposite, irradiated surface it was hypothesized that conductance may have been influenced by photoinhibition within the mesophyll tissue. 相似文献
2.
CO 2 exchange characteristics were studied during the light-stimulated burst of CO 2 uptake (MB) immediately following a period of nocturnal CO 2 fixation in the Crassulacean acid metabolism plant Kalanchoë daigremontiana. During the early parts of the MB, stimulation of net CO 2 uptake by low ambient O 2 concentration (1.5%) was small, and leaves showed the capacity for net CO 2 uptake at low ambient CO 2 partial pressure (30 microbars) and when the MB was interrupted by darkness. During the later phase of the MB, stimulation of net CO 2 uptake by 1.5% O 2 was increased, and net CO 2 loss was recorded both at 30 microbars CO 2 and during dark interruptions. These results suggest that CO 2 fixation during the MB occurs simultaneously via phosphoenolpyruvate carboxylase (predominant during the early phase of the MB) and via ribulose bisphosphate carboxylase (predominant during the later phase of the burst). The magnitude and duration of the MB was increased by a reduction in the length of the dark period and by low (15°C) compared to high (30°C) leaf temperatures. 相似文献
3.
The response of photosynthetic CO 2 assimilation to salinization in 19 year old Prunus salicina was evaluated under field conditions for a 3 year period. The observed decline in CO 2 assimilation capacity was apparently related to increasing leaf chloride (Cl −) content, and independent of changes in leaf carbohydrate status. The response of net CO 2 assimilation (A) to leaf intercellular CO 2 partial pressure (C i) 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 CO 2 assimilation capacity, as determined by the response of A to C i 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 C i 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 CO 2 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.
Relationships between net plant CO 2 exchange rate (CER) and canopy development were examined in `jubilee' tomato over the initial 4 weeks of vegetative growth. A comparison was made between two plant groups that were alternatively exposed to 200 or 800 microeinsteins per square meter per second midday irradiation to establish a differential in net CER. Plants exposed to higher irradiation demonstrated a 2- to 4-fold greater net photosynthetic rate per leaf area and 100% average higher net CO 2 assimilation rate/plant· day. However, leaf-stem growth differed by <50% suggesting a poor relationship to CER. Leaf area growth rate (LAGR) of individual leaves appeared closely related to CER during initial leaf expansion but a greater function of order of emergence in successive leaf growth. LAGR on a per plant basis increased linearly with leaf dry weight but appeared more limited by factors determining maximum leaf enlargement and rate of new leaf development. Net CO 2 assimilation/leaf area and leaf starch consistently declined with time while net CO 2 assimilation plant/day approached a constant rate following 2 to 3 weeks growth. Composite results suggested a simple relationship for sucessive growth where accumulated leaf carbohydrate in excess of 200 milligrams/plant·day could be expected to be partitioned to other plant segments. 相似文献
5.
In well-watered plants of Welwitschia mirabilis, grown in the glass-house under high irradiance conditions, net CO 2 assimilation was almost exclusively observed during the daytime. The plants exhibited a very low potential for Crassulacean acid metabolism, which usually resulted in reduced rates of net CO 2 loss for several hours during the night. In leaves exposed to the diurnal changes in temperature and humidity typical of the natural habitats, CO 2 assimilation rates in the light were markedly depressed under conditions resembling those occurring during midday, when leaf temperatures and the leaf-air vapor pressure differences were high (36°C and 50 millibars bar −1, respectively). Studies on the relationship between CO 2 assimilation rate and intercellular CO 2 partial pressure at various temperatures and humidities showed that this decrease in CO 2 assimilation was largely due to stomatal closure. The increase in the limitation of photosynthesis by CO 2 diffusion, which is associated with the strong decline in stomatal conductance in Welwitschia exposed to midday conditions, may significantly contribute to the higher 13C content of Welwitschia compared to the majority of C 3 species. 相似文献
6.
Net photosynthetic assimilation rate (A), extractable activities of three photosynthetic enzymes, and the concentrations of six metabolites were determined for wheat ( Tricum aestivum L.) leaves as leaf temperature was varied under photorespiring (350 microliters per liter CO 2 and 21% O 2) and under nonphotorespiring conditions (800 microliters per liter CO 2 and 2% O 2). The extractable activity of ribulose-1,5-bisphosphate carboxylase (Rubisco) and fructose-1,6-bisphosphatase declined with increasing leaf temperature from 15 to 45°C. Leaf concentrations of ribulose-1,5-bisphosphate (RuBP) declined slightly between 15 and 25°C but increased to a level which is 4 to 5 times the binding site concentration of Rubisco at leaf temperatures of 35 and 45°C. Leaf concentrations of 3-phosphoglycerate, fructose-6-phosphate, and glucose-6-phosphate all declined with increasing leaf temperature. Outside of the limitations imposed by photorespiration, it is proposed that under high light and at suboptimal temperatures, A is limited by rate of utilization of triose phosphate; at optimal temperatures, by the availability of substrate (CO 2 and RuBP) under photorespiring conditions or utilization of triose phosphate under nonphotorespiring conditions; and at supraoptimal temperatures, by the activation state of Rubisco. 相似文献
7.
Photosynthesis was studied in relation to the carbohydrate status in intact leaves of the C 4 plant Amaranthus edulis. The rate of leaf net CO 2 assimilation, stomatal conductance and intercellular partial pressure of CO 2 remained constant or showed little decline towards the end of an 8-h period of illumination in ambient air (340 bar CO 2, 21% O 2). When sucrose export from the leaf was inhibited by applying a 4-h cold-block treatment (1°C) to the petiole, the rate of photosynthesis rapidly decreased with time. After the removal of the cold block from the petiole, further reduction in photosynthetic rate occurred, and there was no recovery in the subsequent light period. Although stomatal conductance declined with time, intercellular CO 2 partial pressure remained relatively constant, indicating that the inhibition of photosynthesis was not primarily caused by changes in stomatal aperture. Analysis of the leaf carbohydrate status showed a five- to sixfold increase in the soluble sugar fraction (mainly sucrose) in comparison with the untreated controls, whereas the starch content was the same. Leaf osmotic potential increased significantly with the accumulation of soluble sugars upon petiole chilling, and leaf water potential became slightly more negative. After 14 h recovery in the dark, photosynthesis returned to its initial maximum value within 1 h of illumination, and this was associated with a decline in leaf carbohydrate levels overnight. These data show that, in Amaranthus edulis, depression in photosynthesis when translocation is impaired is closely related to the accumulation of soluble sugars (sucrose) in source leaves, indicating feedback control of C 4 photosynthesis. Possible mechanisms by which sucrose accumulation in the leaf may affect the rate of photosynthesis are discussed with regard to the leaf anatomy of C 4 plants.Abbreviations and symbols A
net CO 2 assimilation rate
- Ci
intercellular CO 2 partial pressure
- PEP
phosphoenolpyruvate
- RuBP
ribulose-1,5-bisphosphate
-
water potential
-
osmotic pressure 相似文献
8.
The rate of dark CO 2 efflux from mature wheat ( Triticum aestivum cv Gabo) leaves at the end of the night is less than that found after a period of photosynthesis. After photosynthesis, the dark CO 2 efflux shows complex dependence on time and temperature. For about 30 minutes after darkening, CO 2 efflux includes a large component which can be abolished by transferring illuminated leaves to 3% O 2 and 330 microbar CO 2 before darkening. After 30 minutes of darkness, a relatively steady rate of CO 2 efflux was obtained. The temperature dependence of steady-state dark CO 2 efflux at the end of the night differs from that after a period of photosynthesis. The higher rate of dark CO 2 efflux following photosynthesis is correlated with accumulated net CO 2 assimilation and with an increase in several carbohydrate fractions in the leaf. It is also correlated with an increase in the CO 2 compensation point in 21% O 2, and an increase in the light compensation point. The interactions between CO 2 efflux from carbohydrate oxidation and photorespiration are discussed. It is concluded that the rate of CO 2 efflux by respiration is comparable in darkened and illuminated wheat leaves. 相似文献
9.
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
10.
The mechanism responsible for the inhibition of net carbon exchange (NCE) which was reported previously (DR Geiger et al. 1986 Plant Physiol 82: 468-472) was investigated by applying glyphosate [N-(phosphonomethyl)glycine] to exporting leaves of sugar beet ( Beta vulgaris L.). Leaf internal CO 2 concentration ( Ci) remained constant despite decreases in stomatal conductance and NCE following glyphosate treatment, indicating that the cause of the inhibition was a slowing of carbon assimilation rather than decreased conductance of CO 2. Throughout a range of CO 2 concentrations, NCE rate at a given Ci declined gradually, with the time-series of response curves remaining parallel. Gas exchange measurements revealed that disruption of chloroplast carbon metabolism was an early and important factor in mediating these glyphosate effects, perhaps by slowing the rate of ribulose bisphosphate regeneration. An increase in the CO 2 compensation point accompanied the decrease in NCE and this increase was hastened by stepwise lowering of the ambient CO 2 concentration. Eventually the CO 2 compensation point approached the CO 2 level of air and the difference between internal and external CO 2 concentrations decreased. In control and in glyphosate-treated plants, both carbon assimilation and photorespiration at atmospheric CO 2 level were inhibited to a similar extent of air level of O 2. Maintaining leaves in low O 2 concentration did not prevent the decline in NCE rate. 相似文献
11.
The rate of net CO 2 assimilation (A), the stomatal ( gs) and residual ( gr) conductances to CO 2, the intercellular CO 2 concentration, the CO 2 compensation points at 21% O 2 (Γ 21) and at 2% O 2 (Γ 2), and the amounts of dry matter, nitrogen, and carbohydrates were determined, from anthesis through grain filling, in the flag leaf blade and sheath of spring wheat ( Triticum aestivum L. cv Kolibri). The nitrogen content and the rate of net CO 2 assimilation declined slowly until the onset of senescence in both organs, about 3 weeks after anthesis. During senescence the reduction of A in both organs was not primarily caused by a decrease in gs; the main factor is the decrease in gr. From values of Γ 21 and Γ 2 it is suggested that the rate of respiration in the light contributing to the CO 2 compensation point is higher in sheaths than in blades irrespective of the O 2 level considered. The role of sheaths storing and later transporting assimilates to the developing grains seems to be more important for shoot yield than that of sheaths functioning as photosynthetic organs after the onset of senescence occurs. It is suggested that accumulation of carbohydrates in leaves might somehow trigger senescence in the flag leaf blade and sheath simultaneously. 相似文献
12.
Interactive effects of root restriction and atmospheric CO 2 enrichment on plant growth, photosynthetic capacity, and carbohydrate partitioning were studied in cotton seedlings ( Gossypium hirsutum L.) grown for 28 days in three atmospheric CO 2 partial pressures (270, 350, and 650 microbars) and two pot sizes (0.38 and 1.75 liters). Some plants were transplanted from small pots into large pots after 20 days. Reduction of root biomass resulting from growth in small pots was accompanied by decreased shoot biomass and leaf area. When root growth was less restricted, plants exposed to higher CO 2 partial pressures produced more shoot and root biomass than plants exposed to lower levels of CO 2. In small pots, whole plant biomass and leaf area of plants grown in 270 and 350 microbars of CO 2 were not significantly different. Plants grown in small pots in 650 microbars of CO 2 produced greater total biomass than plants grown in 350 microbars, but the dry weight gain was found to be primarily an accumulation of leaf starch. Reduced photosynthetic capacity of plants grown at elevated levels of CO 2 was clearly associated with inadequate rooting volume. Reductions in net photosynthesis were not associated with decreased stomatal conductance. Reduced carboxylation efficiency in response to CO 2 enrichment occurred only when root growth was restricted suggesting that ribulose-1,5-bisphosphate carboxylase/oxygenase activity may be responsive to plant source-sink balance rather than to CO 2 concentration as a single factor. When root-restricted plants were transplanted into large pots, carboxylation efficiency and ribulose-1,5-bisphosphate regeneration capacity increased indicating that acclimation of photosynthesis was reversible. Reductions in photosynthetic capacity as root growth was progressively restricted suggest sink-limited feedback inhibition as a possible mechanism for regulating net photosynthesis of plants grown in elevated CO 2. 相似文献
13.
During the period of most active leaf expansion, the foliar dark respiration rate of soybeans ( Glycine max cv Williams), grown for 2 weeks in 1000 microliters CO 2 per liter air, was 1.45 milligrams CO 2 evolved per hour leaf density thickness, and this was twice the rate displayed by leaves of control plants (350 microliters CO 2 per liter air). There was a higher foliar nonstructural carbohydrate level ( e.g. sucrose and starch) in the CO 2 enriched compared with CO 2 normal plants. For example, leaves of enriched plants displayed levels of nonstructural carbohydrate equivalent to 174 milligrams glucose per gram dry weight compared to the 84 milligrams glucose per gram dry weight found in control plant leaves. As the leaves of CO 2 enriched plants approached full expansion, both the foliar respiration rate and carbohydrate content of the CO 2 enriched leaves decreased until they were equivalent with those same parameters in the leaves of control plants. A strong positive correlation between respiration rate and carbohydrate content was seen in high CO 2 adapted plants, but not in the control plants. Mitochondria, isolated simultaneously from the leaves of CO2 enriched and control plants, showed no difference in NADH or malate-glutamate dependent O2 uptake, and there were no observed differences in the specific activities of NAD+ linked isocitrate dehydrogenase and cytochrome c oxidase. Since the mitochondrial O2 uptake and total enzyme activities were not greater in young enriched leaves, the increase in leaf respiration rate was not caused by metabolic adaptations in the leaf mitochondria as a response to long term CO2 enrichment. It was concluded, that the higher respiration rate in the enriched plant's foliage was attributable, in part, to a higher carbohydrate status. 相似文献
14.
To evaluate daytime and nighttime carbon balance and assimilate export in soybean ( Glycine max [L.] Merrill) leaves at different photon flux densities, rates of CO 2 exchange, specific leaf weights, and concentrations of sucrose and starch were measured at intervals in leaves of pod-bearing `Amsoy 71' and `Wells II' plants grown in a controlled environment room. Assimilate export was estimated from CO 2 exchange and change in specific leaf weight. Total diurnal assimilate export was similar for both cultivars. Large cultivar differences existed, however, in the partitioning of carbon into starch reserves and the relative amounts of assimilate exported during the day and the night. Total amounts of both daytime and nighttime export increased with increasing photon flux density, as did sucrose and starch concentrations, specific leaf weight, and rate of respiratory carbohydrate loss at night. Cultivar differences in nighttime rate of export were more closely related to the differences in amount of assimilate available at the end of the day than to differences in daytime rate of net CO 2 assimilation. Daytime rates of export, however, were closely related to daytime rates of net CO 2 assimilation within each cultivar. The total amount of starch depleted during the 10-hour night increased as starch concentration at the beginning of the night increased. 相似文献
15.
A complementary DNA for the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) was cloned from tobacco ( Nicotiana tabacum) and fused in the antisense orientation to the cauliflower mosaic virus 35S promoter. This antisense gene was introduced into the tobacco genome, and the resulting transgenic plants were analyzed to assess the effect of the antisense RNA on Rubisco activity and photosynthesis. The mean content of extractable Rubisco activity from the leaves of 10 antisense plants was 18% of the mean level of activity of control plants. The soluble protein content of the leaves of anti-small subunit plants was reduced by the amount equivalent to the reduction in Rubisco. There was little change in phosphoribulokinase activity, electron transport, and chlorophyll content, indicating that the loss of Rubisco did not affect these other components of photosynthesis. However, there was a significant reduction in carbonic anhydrase activity. The rate of CO 2 assimilation measured at 1000 micromoles quanta per square meter per second, 350 microbars CO 2, and 25°C was reduced by 63% (mean value) in the antisense plants and was limited by Rubisco activity over a wide range of intercellular CO 2 partial pressures (p i). In control leaves, Rubisco activity only limited the rate of CO 2 assimilation below a p i of 400 microbars. Despite the decrease in photosynthesis, there was no reduction in stomatal conductance in the antisense plants, and the stomata still responded to changes in p i. The unchanged conductance and lower CO 2 assimilation resulted in a higher p i, which was reflected in greater carbon isotope discrimination in the leaves of the antisense plants. These results suggest that stomatal function is independent of total leaf Rubisco activity. 相似文献
16.
The net CO 2 assimilation by leaves of maize ( Zea mays L. cv. Adonis) plants subjected to slow or rapid dehydration decreased without changes in the total extractable activities of phospho enolpyruvate carboxylase (PEPC), malate dehydrogenase (MDH) and malic enzyme (ME). The phosphorylation state of PEPC extracted from leaves after 2–3 h of exposure to light was not affected by water deficit, either. Moreover, when plants which had been slowly dehydrated to a leaf relative water content of about 60% were rehydrated, the net CO 2 assimilation by leaves increased very rapidly without any changes in the activities of MDH, ME and PEPC or phosphorylation state of PEPC. The net CO 2-dependent O 2 evolution of a non-wilted leaf measured with an oxygen electrode decreased as CO 2 concentration increased and was totally inhibited when the CO 2 concentration was about 10%. Nevertheless, high CO 2 concentrations (5–10%) counteracted most of the inhibitory effect of water deficit that developed during a slow dehydration but only counteracted a little of the inhibitory effect that developed during a rapid dehydration. In contrast to what could be observed during a rapidly developing water deficit, inhibition of leaf photosynthesis by cis-abscisic acid could be alleviated by high CO 2 concentrations. These results indicate that the inhibition of leaf net CO 2 uptake brought about by water deficit is mainly due to stomatal closure when a maize plant is dehydrated slowly while it is mainly due to inhibition of non-stomatal processes when a plant is rapidly dehydrated. The photosynthetic apparatus of maize leaves appears to be as resistant to drought as that of C 3 plants. The non-stomatal inhibition observed in rapidly dehydrated leaves might be the result of either a down-regulation of the photosynthetic enzymes by changes in metabolite pool sizes or restricted plasmodesmatal transport between mesophyll and bundle-sheath cells. 相似文献
17.
Cotton plants were grown in late spring under full sunlight in glasshouses containing normal ambient partial pressure of CO 2 (32±2Pa) and enriched partial pressure of CO 2 (64±1.5Pa) and at four levels of nitrogen nutrition. Thirty-five days after planting, the total dry weights of high CO 2-grown plants were 2- to 3.5-fold greater than plants grown in normal ambient CO 2 partial pressure. Depending on nitrogen nutrition level, non-structural carbohydrate content (mainly starch) in the leaves of plants grown in normal CO 2 was between 4 and 37% of the total leaf dry weight compared to 39 to 52% in the leaves of high CO 2-grown plants. Specific leaf weight calculated using total dry weight was 1.6- to 2-fold greater than that based on structural dry weight. In high CO 2-grown plants the amount of non-structural carbohydrate translocated from the leaves at night was between 10 and 20% of the level at the end of the photoperiod. This suggests that the plant was unable to utilize all the carbohydrate it assimilated in elevated CO 2 atmosphere. While there was a 1.5-fold enhancement in the rate of CO 2 assimilation in plants grown in 64 Pa CO 2, there was, however, some evidence to suggest that the activities of other metabolic pathways in the plants were not stimulated to the same extent by the enriched CO 2 atmosphere. This resulted in massive accumulation of non-structural carbohydrate, particularly at low level of nitrogen nutrition.Abbreviations A
rate of CO 2 assimilation
- PPFD
photosynthetic photo flux density
- NAR
net assimilation rate
- pCO 2
partial pressure of CO 2
- RGR
relative growth rate 相似文献
18.
Potato plants ( Solanum tuberosum L. cv. Bintje) were grown to maturity in open-top chambers under three carbon dioxide (CO 2; ambient and 24 h d −1 seasonal mean concentrations of 550 and 680 μmol mol −1) and two ozone levels (O 3; ambient and an 8 h d −1 seasonal mean of 50 nmol mol −1). Chlorophyll content, photosynthetic characteristics, and stomatal responses were determined to test the hypothesis that elevated atmospheric CO 2 may alleviate the damaging influence of O 3 by reducing uptake by the leaves. Elevated O 3 had no detectable effect on photosynthetic characteristics, leaf conductance, or chlorophyll content, but did reduce SPAD values for leaf 15, the youngest leaf examined. Elevated CO 2 also reduced SPAD values for leaf 15, but not for older leaves; destructive analysis confirmed that chlorophyll content was decreased. Leaf conductance was generally reduced by elevated CO 2, and declined with time in the youngest leaves examined, as did assimilation rate ( A). A generally increased under elevated CO 2, particularly in the older leaves during the latter stages of the season, thereby increasing instantaneous transpiration efficiency. Exposure to elevated CO 2 and/or O 3 had no detectable effect on dark-adapted fluorescence, although the values decreased with time. Analysis of the relationships between assimilation rate and intercellular CO 2 concentration and photosynthetically active photon flux density showed there was initially little treatment effect on CO 2-saturated assimilation rates for leaf 15. However, the values for plants grown under 550 μmol mol −1 CO 2 were subsequently greater than in the ambient and 680 μmol mol −1 treatments, although the beneficial influence of the former treatment declined sharply towards the end of the season. Light-saturated assimilation was consistently greater under elevated CO 2, but decreased with time in all treatments. The values decreased sharply when leaves grown under elevated CO 2 were measured under ambient CO 2, but increased when leaves grown under ambient CO 2 were examined under elevated CO 2. The results obtained indicate that, although elevated CO 2 initially increased assimilation and growth, these beneficial effects were not necessarily sustained to maturity as a result of photosynthetic acclimation and the induction of earlier senescence. 相似文献
19.
Summary CO 2 exchange and air flow through the stomata were measured in leaf sections of Zea mays at temperatures between 7 and 52° and under optimal water supply. The results were summarized in polynomials fitted to the data.In leaf samples brought from 16° and darkness into different experimental temperatures and light, CO 2 assimilation has a maximum near 30°. Above 37° (in other experiments above 41°), net CO 2 uptake stops abruptly and is replaced by CO 2 evolution in light. If a 1-hr treatment with 25° and light is inserted between darkness and the experimental temperatures, the threshold above which the assimilatory system collapses shifts 3 degrees upwards, to 40° (or 44°); the decline of CO 2 assimilation with high temperatures is less steep than without pretreatment; and the upper compensation point moves upscale by as much as 5 degrees.Stomatal conductance for CO 2 does not, in general, follow an optimum curve with temperature. Between 15 and 35° it is approximately proportional to net CO 2 assimilation, indicating control by CO 2; but above 35°, stomatal aperture increases further with temperature (and so does stomatal variability): the stomata escape the control by CO 2 and above 40° may be wide open even if CO 2 is being evolved. Stomatal conductance for CO 2 below 15° may also be larger than would be proportional to CO 2 assimilation.Net CO 2 assimilation and stomatal conductance at 25° were reduced if the leaf samples were pretreated with temperatures below approximately 20° and above 30°. Stomata were more sensitive to past temperatures than was CO 2 assimilation. 相似文献
20.
To assess the variability of net photosynthetic CO 2 exchange per unit leaf area and to construct budgets for stands of field-grown tobacco ( Nicotiana tabacum, Connecticut Broadleaf), a number of short-time measurements were made on all available leaf positions on two varieties using a hand-held transparent chamber for conducting gas exchange measurements on leaves. Measurements of net CO 2 exchange were carried out on 18 separate days during a 35-day period, beginning 22 days after the seedlings were transplanted to the field. Gas exchange assays on leaves were conducted under ambient conditions of temperature and light intensity at all times of day. Solar radiation was monitored throughout the period, and losses of respiratory CO 2 from stems, roots, and leaves (in the dark) were estimated. A simple model was proposed to relate daily total CO 2 input to irradiance and total leaf area. The total leaf area was assumed to be a function of day number. Dark respiratory losses accounted for 41% to 47% of total CO 2 assimilation. Analysis of variance indicated that the two varieties were not significantly different in whole plant rate of CO 2 fixation per unit of leaf area. CO 2 input was closely associated with leaf area within each variety. Throughout the experiment, the difference between the two varieties in total leaf area per plant was the largest single factor in determining net CO 2 inputs. The cumulative dry weight increase for each variety was similar to the prediction of net dry matter input obtained by gas exchange measurements, thus confirming the close relationship between total plant net CO 2 assimilation and dry weight yield. 相似文献
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