Photosynthesis and Growth of Water Hyacinth under CO(2) Enrichment

Water hyacinth (Eichhornia crassipes [Mart.] Solms) plants were grown in environmental chambers at ambient and enriched CO₂ levels (330 and 600 microliters CO₂ per liter). Daughter plants (ramets) produced in the enriched CO₂ gained 39% greater dry weight than those at ambient CO₂, but the original mother plants did not. The CO₂ enrichment increased the number of leaves per ramet and leaf area index, but did not significantly increase leaf size or the number of ramets formed. Flower production was increased 147%. The elevated CO₂ increased the net photosynthetic rate of the mother plants by 40%, but this was not maintained as the plants acclimated to the higher CO₂ level. After 14 days at the elevated CO₂, leaf resistance increased and transpiration decreased, especially from the adaxial leaf surface. After 4 weeks in elevated as compared to ambient CO₂, ribulose bisphosphate carboxylase activity was 40% less, soluble protein content 49% less, and chlorophyll content 26% less; whereas starch content was 40% greater. Although at a given CO₂ level the enriched CO₂ plants had only half the net photosynthetic rate of their counterparts grown at ambient CO₂, they showed similar internal CO₂ concentrations. This suggested that the decreased supply of CO₂ to the mesophyll, as a result of the increased stomatal resistance, was counterbalanced by a decreased utilization of CO₂. Photorespiration and dark respiration were lower, such that the CO₂ compensation point was not altered. The photosynthetic light and CO₂ saturation points were not greatly changed, nor was the O₂ inhibition of photosynthesis (measured at 330 microliters CO₂ per liter). It appears that with CO₂ enrichment the temporary increase in net photosynthesis produced larger ramets. After acclimation, the greater total ramet leaf area more than compensated for the lower net photosynthetic rate on a unit leaf area basis, and resulted in a sustained improvement in dry weight gain.     

Effects of Atmospheric CO(2) Enrichment on Photosynthesis, Respiration, and Growth of Sour Orange Trees

Numerous net photosynthetic and dark respiratory measurements were made over a period of 4 years on leaves of 24 sour orange (Citrus aurantium) trees; 8 of them growing in ambient air at a mean CO₂ concentration of 400 microliters per liter, and 16 growing in air enriched with CO₂ to concentrations approaching 1000 microliters per liter. Over this CO₂ concentration range, net photosynthesis increased linearly with CO₂ by more than 200%, whereas dark respiration decreased linearly to only 20% of its initial value. These results, together with those of a comprehensive fine-root biomass determination and two independent aboveground trunk and branch volume inventories, suggest that a doubling of the air's current mean CO₂ concentration of 360 microliters per liter would enhance the growth of the trees by a factor of 3.8.     

Effects of CO(2)-Enrichment and of Aminoacetonitrile on Growth and Photosynthesis of Photoautotrophic Calli of Nicotiana plumbaginifolia

Photoautotrophic calli of Nicotiana plumbaginifolia were grown for 3 weeks under two CO₂ concentrations (500 and 20,000 microliters of CO₂ per liter). Calli cultured at high CO₂ exhibited a two-fold higher rate of growth. At CO₂ test levels, these calli were characterized by a lower net photosynthetic capacity than calli cultured at low CO₂. This diminution due to CO₂ adaptation could be ascribed to a 170% stimulation of dark respiration, a 40% decrease in total ribulose-1,5-bisphosphate carboxylase (Rubisco) activity, and also to a feedback inhibition of photosynthesis: high CO₂ grown calli contained about 5.5-fold more sucrose and three-fold less orthophosphate (Pi) than low CO₂ grown calli. Whether the decrease in Rubisco activity is related to the accumulation of sucrose and to the Pi limitation is discussed. Both calli exhibited a Warburg-effect showing the existence of active photorespiration at low CO₂. In calli grown at low CO₂ with 5 millimolar aminoacetonitrile (AAN), an inhibitor of the glycolate pathway, fresh weight decreased by 25% and chlorophyll content by 40%, dark respiration increased by 50% and net CO₂ uptake decreased by about 60% at 340 microliters of CO₂ per liter and 35% at 10,000 microliters of CO₂ per liter. In these calli, glutamine and glutamate contents were half of control calli. In contrast, AAN did not provoke any noticeable effect in calli grown at high CO₂. In photoautotrophic calli, the inhibition of the glycolate pathway by AAN results in severe perturbations in glutamate metabolism and in chlorophyll biosynthesis.     

延长光照时间对烟草叶片生长发育及光合特性的影响

以烤烟品种‘云烟87’为材料,采用夜间人工补光的方式,以自然光照时间为对照,设置增加1h、2h和3h光照3个处理,研究延长光照时间对烟草生长发育、叶绿素含量及光合作用、叶绿素荧光参数和光响应曲线的影响。结果表明:(1)与对照相比,延长光照时间2h处理下烟株叶长、叶宽、株高显著增加,1h、3h处理影响不显著。(2)延长光照处理显著降低比叶面积,提高叶片叶绿素a、b、叶绿素a+b、类胡萝卜素含量,但1h、3h处理的变化幅度小于2h处理。(3)延长光照时间1h和2h处理下叶片净光合速率(Pn)、气孔导度(Gs)、胞间CO2浓度(Ci)显著升高,3h处理影响不大;延长光照处理显著提高了PSⅡ最大光化学量子效率(Fv/Fm)、PSⅡ实际光化学量子效率(ΦPSⅡ)、光化学淬灭系数(qP),降低了非光化学淬灭系数(NPQ),其中2h处理影响幅度最大,但对初始荧光强度F0影响不显著;延长光照处理下烟草叶片的最大净光合速率(Pmax)和光饱和点(Isat)均升高,但光补偿点(Ic)没有明显的变化。研究表明,适当延长光照时间有利于叶片生长发育和干物质积累,提高叶绿素含量,促进光合作用,缓解光抑制现象,充分利用光能,提高叶片光合同化效率。     

Effects of O(2) and CO(2) Concentrations on Quantum Yields of Photosystems I and II in Tobacco Leaf Tissue

The interactive effects of irradiance and O₂ and CO₂ levels on the quantum yields of photosystems I and II have been studied under steady-state conditions at 25°C in leaf tissue of tobacco (Nicotiana tabacum). Assessment of radiant energy utilization in photosystem II was based on changes in chlorophyll fluorescence yield excited by a weak measuring beam of modulated red light. Independent estimates of photosystem I quantum yield were based on the light-dark in vivo absorbance change at 830 nanometers, the absorption band of P700⁺. Normal (i.e. 20.5%, v/v) levels of O₂ generally enhanced photosystem II quantum yield relative to that measured under 1.6% O₂ as the irradiance approached saturation. Photorespiration is suspected to mediate such positive effects of O₂ through increases in the availability of CO₂ and recycling of orthophosphate. Conversely, at low intercellular CO₂ concentrations, 41.2% O₂ was associated with lower photosystem II quantum yield compared with that observed at 20.5% O₂. Inhibitory effects of 41.2% O₂ may occur in response to negative feedback on photosystem II arising from a build-up in the thylakoid proton gradient during electron transport to O₂. Covariation between quantum yields of photosystems I and II was not affected by concentrations of either O₂ or CO₂. The dependence of quantum yield of electron transport to CO₂ measured by gas exchange upon photosystem II quantum yield as determined by fluorescence was unaffected by CO₂ concentration.     

Leaf Photosynthesis and Respiration of High CO(2)-Grown Tobacco Plants Selected for Survival under CO(2) Compensation Point Conditions

Four self-pollinated, doubled-haploid tobacco, (Nicotiana tabacum L.) lines (SP422, SP432, SP435, and SP451), selected as haploids by survival in a low CO₂ atmosphere, and the parental cv Wisconsin-38 were grown from seed in a growth room kept at high CO₂ levels (600-700 parts per million). The selected plants were much larger (especially SP422, SP432, and SP451) than Wisconsin-38 nine weeks after planting. The specific leaf dry weight and the carbon (but not nitrogen and sulfur) content per unit area were also higher in the selected plants. However, the chlorophyll, carotenoid, and alkaloid contents and the chlorophyll a/b ratio varied little. The net CO₂ assimilation rate per unit area measured in the growth room at high CO₂ was not higher in the selected plants. The CO₂ assimilation rate versus intercellular CO₂ curve and the CO₂ compensation point showed no substantial differences among the different lines, even though these plants were selected for survival under CO₂ compensation point conditions. Adult leaf respiration rates were similar when expressed per unit area but were lower in the selected lines when expressed per unit dry weight. Leaf respiration rates were negatively correlated with specific leaf dry weight and with the carbon content per unit area and were positively correlated with nitrogen and sulfur content of the dry matter. The alternative pathway was not involved in respiration in the dark in these leaves. The better carbon economy of tobacco lines selected for low CO₂ survival was not apparently related to an improvement of photosynthesis rate but could be related, at least partially, to a significantly reduced respiration (mainly cytochrome pathway) rate per unit carbon.     

Effects of O2 and CO2 on Nonsteady-State Photosynthesis (Further Evidence for Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Limitation)

The effects of CO2 and O2 on nonsteady-state photosynthesis following an increase in photosynthetic photon flux density (PPFD) were examined in Spinacia oleracea to investigate the hypotheses that (a) a slow exponential phase (the ribulose-1,5-bisphosphate carboxylase/oxygenase [Rubisco] phase) of nonsteady-state photosynthesis is primarily limited by Rubisco activity and (b) Rubisco activation involves two sequential, light-dependent processes as described in a previous study (I.E. Woodrow, K.A. Mott [1992] Plant Physiol 99: 298-303). Photosynthesis was found to be sensitive to O2 during the Rubisco phase in the approach of photosynthesis to steady state. Analyses of this sensitivity to O2 showed that the control coefficient for Rubisco was approximately equal to 1 during this phase, suggesting that Rubisco was the primary limitation to photosynthesis. O2 had almost no effect on the kinetics (described using a relaxation time, [tau] of the Rubisco phase for leaves starting in darkness or for leaves starting in low PPFD, but [tau] was substantially higher in the former case. CO2 was found to affect both the rate of photosynthesis and the magnitude of [tau] for the Rubisco phase. The [tau] value for the Rubisco phase was found to be negatively correlated with intercellular CO2 concentration (ci), and leaves starting in darkness had higher values of [tau] at any ci than leaves starting in low PPFD. The effects of CO2 and O2 on the Rubisco phase are consistent with the existence of two sequential, light-dependent processes in the activation of Rubisco if neither process is sensitive to O2 and only the second process is sensitive to CO2. The implications of the data for the mechanism of Rubisco activation and for the effects of stomatal conductance on nonsteady-state photosynthesis are discussed.     

Interactive Effects of CO(2) and O(2) in Soil on Root and Top Growth of Barley and Peas

Barley and pea plants were grown under several regimens of different compositions of soil atmosphere, the O₂ concentration varying from 0 to 21% and the CO₂ concentration from 0 to 8%. In absence of CO₂, the effect of O₂ on root length in barley was characterized by equal root lengths within the range of 21 to 7% O₂ and a steep decline between 7 and 0%. In peas, while showing the same general response, the decline occurred between 14 and 7% O₂. Root numbers of the seminal roots of barley decreased already with reduction in O₂ concentration from 21 to 14%. Dry matter production was affected somewhat differently by O₂ and CO₂ concentration. Dry matter production in barley was reduced at 14% O₂ while root length decreased between 7 and 0%. In peas, dry matter production was favored by low CO₂ concentrations except where there was no oxygen. At 21% O₂, increasing CO₂ concentrations did not seem to affect root length up to concentrations of 2% CO₂. At 8% CO₂, root length was decreased. The inter-active effects of CO₂ and O₂ are characterized by a reduced susceptibility to CO₂ at O₂ values below 7%, and a very deleterious effect of 8% CO₂ at 7% O₂.     

Photosynthesis of Ulva sp: III. O(2) Effects, Carboxylase Activities, and the CO(2) Incorporation Pattern

Ulva, a common green seaweed, performs at the biochemical level as a typical C₃ plant. Over 90% of label was found in glycerate 3-phosphate following a 3 second ¹⁴C pulse in the light, and the label was subsequently transferred to sugars. Also, the level of ribulose-1,5-bisphosphate carboxylase activity in crude extracts was about 10 times higher than that of phosphoenolpyruvate carboxylase. Concerning gas exchange, photosynthetic rates of Ulva showed no O₂ sensitivity, indicating that photorespiratory CO₂ losses are repressed as in C₄ plants. This apparent anomaly could be explained by the efficient HCO₃⁻ uptake system of Ulva which might concentrate CO₂ to the chloroplasts, thus suppressing the oxygenase activity of ribulose-1,5-bisphosphate carboxylase.     

Effects of CO(2) and O(2) on the Photosynthetic O(2) Evolution of Spirodela polyrrhiza Turions

Net photosynthetic rates of Spirodela polyrrhiza turions, at low O₂ levels, were 6.2 and 38.8 micromoles O₂ per gram fresh weight per hour at 1 millimolar HCO₃⁻ and CO₂ saturation, respectively, and much lower in a regular low-pH growth solution. Air equilibration O₂ concentrations decreased rates considerably, except at CO₂ saturation. The surfacing rate of turions in various inorganic carbon surroundings correlated positively with their photosynthetic rates, but were the same at high and low O₂ levels. The relevance of these findings in relation to environmental conditions conductive to germination of autotrophically growing turions is discussed.     

壳寡糖对烟草幼苗生长和光合作用及与其相关生理指标的影响

采用酶解法获得的壳寡糖,处理烟草幼苗的结果显示,0．01mg·L^-1壳寡糖对烟草幼苗生长有促进作用,幼苗株高、叶面积增加;功能叶片中叶绿素含量、净光合速率（Pn）、气孔导度（Gs）、蒸腾速率（Tr）和胞间CO2浓度（Ci）升高;气孔限制值（Ls）下降。而高浓度（100mg·L^-1）壳寡糖处理的则抑制生长。促进烟草幼苗生长最适的壳寡糖浓度为0．01mg·L^-1,施用两次的效果优于一次的。     

Non-autotrophic CO2 Fixation during Shoot Formation in Tobacco Callus

Non-autotrophic carbon fixation has been studied during growthof tobacco callus cultured in dark under shoot-forming (SF)and non-shoot-forming (NSF) conditions. The enzymes involvedin malate metabolism—phosphoenolpyruvate carboxylase,malic dehydrogenase, glutamic-oxalacetic transaminase, and malicenzyme—increased sharply during the first 4 d of cultureparticularly in SF tissue. The activities of the enzymes studiedwere considerably greater in SF than in NSF tissue. There wasa dramatic increase in malate content in SF tissue during thefirst 4 d of culture. Subsequently malate was rapidly depletedduring the time of organogenesis. In NSF tissue there was acontinuous build-up of malate content throughout the cultureperiod. We suggest that malate derived from dark fixation ofCO₂ plays differing roles in NSF (callus) and SF tissues. Inthe former, malate acts primarily as an osmotic solute regulating,at least in part, cell expansion between successive cell divisions.In shoot-forming tissue, on the other hand, malate preferentiallyprovides NADPH for reductive biosynthesis.     

The Effect of Temperature on the Occurrence of O(2) and CO(2) Insensitive Photosynthesis in Field Grown Plants

The sensitivity of photosynthesis to O₂ and CO₂ was measured in leaves from field grown plants of six species (Phaseolus vulgaris, Capsicum annuum, Lycopersicon esculentum, Scrophularia desertorum, Cardaria draba, and Populus fremontii) from 5°C to 35°C using gas-exchange techniques. In all species but Phaseolus, photosynthesis was insensitive to O₂ in normal air below a species dependent temperature. CO₂ insensitivity occurred under the same conditions that resulted in O₂ insensitivity. A complete loss of O₂ sensitivity occurred up to 22°C in Lycopersicon but only up to 6°C in Scrophularia. In Lycopersicon and Populus, O₂ and CO₂ insensitivity occurred under conditions regularly encountered during the cooler portions of the day. Because O₂ insensitivity is an indicator of feedback limited photosynthesis, these results indicate that feedback limitations can play a role in determining the diurnal carbon gain in the field. At higher partial pressures of CO₂ the temperature at which O₂ insensitivity occurred was higher, indicating that feedback limitations in the field will become more important as the CO₂ concentration in the atmosphere increases.     

Effect of CO(2), O(2), and Light on Photosynthesis and Photorespiration in Wheat

Unidirectional O₂ fluxes were measured with ¹⁸O₂ in a whole plant of wheat cultivated in a controlled environment. At 2 or 21% O₂, O₂ uptake was maximum at 60 microliters per liter CO₂. At lower CO₂ concentrations, it was strongly inhibited, as was photosynthetic O₂ evolution. At 2% O₂, there remained a substantial O₂ uptake, even at high CO₂ level; the O₂ evolution was inhibited at CO₂ concentrations under 330 microliters per liter. The O₂ uptake increased linearly with light intensity, starting from the level of dark respiration. No saturation was observed at high light intensities. No significant change in the gas-exchange patterns occurred during a long period of the plant life. An adaptation to low light intensities was observed after 3 hours illumination. These results are interpreted in relation to the functioning of the photosynthetic apparatus and point to a regulation by the electron acceptors and a specific action of CO₂. The behavior of the O₂ uptake and the study of the CO₂ compensation point seem to indicate the persistence of mitochondrial respiration during photosynthesis.     

Ethylene Contamination of CO(2) Cylinders: Effects on Plant Growth in CO(2) Enrichment Studies

The mechanical extensibilities of stage IVb Phycomyces were measured before and after a humidified wind stimulus. We find that when the humidity of the wind is greater than that of the ambient air, there is an increase in the mechanical extensibility of the cell wall. We also find that a step decrease in wind humidity results in a decrease in the mechanical extensibility of the cell wall.     

Photosynthesis and Activation of Ribulose Bisphosphate Carboxylase in Wheat Seedlings : Regulation by CO(2) and O(2)

Photosynthetic carbon assimilation in plants is regulated by activity of the ribulose 1,5-bisphosphate (RuBP) carboxylase/oxygenase. Although the carboxylase requires CO₂ to activate the enzyme, changes in CO₂ between 100 and 1,400 microliters per liter did not cause changes in activation of the leaf carboxylase in light. With these CO₂ levels and 21% O₂ or 1% or less O₂, the levels of ribulose bisphosphate were high and not limiting for CO₂ fixation. With high leaf ribulose bisphosphate, the K_act(CO₂) of the carboxylase must be lower than in dark, where RuBP is quite low in leaves. When leaves were illuminated in the absence of CO₂ and O₂, activation of the carboxylase dropped to zero while RuBP levels approached the binding site concentration of the carboxylase, probably by forming the inactive enzyme-RuBP complex.

The mechanism for changing activation of the RuBP carboxylase in the light involves not only Mg²⁺ and pH changes in the chloroplast stroma, but also the effects of binding RuBP to the enzyme. In light when RuBP is greater than the binding site concentration of the carboxylase, Mg²⁺ and pH most likely determine the ratio of inactive enzyme-RuBP to active enzyme-CO₂-Mg²⁺-RuBP forms. Higher irradiances favor more optimal Mg²⁺ and pH, with greater activation of the carboxylase and increased photosynthesis.

     

Effects of Irradiance on the in Vivo CO(2):O(2) Specificity Factor in Tobacco Using Simultaneous Gas Exchange and Fluorescence Techniques

The effects of gas phase O₂ concentration (1%, 20.5%, and 42.0%, v/v) on the quantum yield of net CO₂ fixation and fluorescence yield of chlorophyll a are examined in leaf tissue from Nicotiana tabacum at normal levels of CO₂ and 25 to 30°C. Detectable decreases in nonphotochemical quenching of absorbed excitation occurred at the higher O₂ levels relative to 1% O₂ when irradiance was nearly or fully saturating for photosynthesis. Photochemical quenching was increased by high O₂ levels only at saturating irradiance. Simultaneous measurements of CO₂ and H₂O exchange and fluorescence yield permit estimation of partitioning of linear photosynthetic electron transport between net CO₂ fixation and O₂-dependent, dissipative processes such as photorespiration as a function of leaf internal CO₂ concentration. Changes in the in vivo CO₂:O₂ `specificity factor' (K_sp) with increasing irradiance are examined. The magnitude K_sp was found to decline from a value of 85 at moderate irradiance to 68 at very low light, and to 72 at saturating photon flux rates. The results are discussed in terms of the applicability of the ribulose bisphosphate carboxylase/oxygenase enzyme model to photosynthesis in vivo.     

Photosynthesis and Plant Growth at Elevated Levels of CO2

In this review, we discuss the effects of elevated CO₂ levelson photosynthesis in relation to the whole plant growth in terrestrialhigher C₃ plants. Short-term CO₂ enrichment stimulates the rateof photosynthesis. Plant mass is also enhanced by CO₂ enrichment.However, the effects of long-term CO₂ enrichment on photosynthesisare variable. Generally, the prolonged exposure to CO₂ enrichmentreduces the initial stimulation of photosynthesis in many species,and frequently suppresses photosynthesis. These responses areattributed to secondary responses related to either excess carbohydrateaccumulation or decreased N content rather than direct responsesto CO₂. Accumulation of carbohydrates in leaves may lead tothe repression of photosynthetic gene expression and excessstarch seems to hinder CO₂ diffusion. Therefore, the specieswhich have the sink organs for carbohydrate accumulation donot show the suppression of photosynthesis. The suppressionof photosynthesis by CO₂ enrichment is always associated withdecreases in leaf N and Rubisco contents. These decreases arenot due to dilution of N caused by a relative increase in theplant mass but are the result of a decrease in N allocationto leaves at the level of the whole plant, and the decreasein Rubisco content is not selective. Leaf senescence and plantdevelopment are also accelerated by CO₂ enrichment. However,they are independent of each other in some species. Thus, variousresponses to CO₂ observed at the level of a single leaf resultfrom manifold responses at the level of the whole plant grownunder conditions of CO₂ enrichment. (Received July 8, 1999; Accepted August 12, 1999)     

不同光质对烟草叶片生长及光合作用的影响

通过对烟草植株覆盖白、红、黄、蓝、紫色滤膜获得不同光质,研究了光质对烟叶生长及光合作用的影响。结果表明,与白膜处理相比,红膜与蓝膜处理下的烟草叶片较厚,比叶面积较小,叶绿素a/b比值、净光合速率、可变荧光强度（Fv）和最大荧光强度（Fm）的比值Fv/Fm（PSⅡ最大光化学量子效率）、PSⅡ实际光化学量子效率（ΦPSⅡ）、光饱和点和CO2饱和点均较高。黄膜处理下的叶片较白膜处理的更薄,净光合速率、Fv/Fm、ΦPSⅡ、光饱和点、CO2饱和点均较低。紫膜处理的叶片比叶面积比白膜处理的小,净光合速率和Fv/Fm比白膜的大。实验结果表明红光、蓝光和紫光促进了烟叶的生长,这种促进作用是与其高光合效率紧密相连的;而黄光对烟叶的生长有一定程度的抑制作用。