Response of Photosynthesis and Dark-CO2-Fixation to Light, CO2 and Temperature in Leaf Slices under Osmotic Stress

Photosynthesis and dark-CO₂-fixation were measured in vacuum-infiltratedleaf slices from the mesophyte Spinacia oleracea and the Mediterraneanxerophyte Arbutus unedo under hypertonic stress as a functionof light-intensity, CO₂-concentration and temperature, in theabsence of stomatal control. Under hypertonic stress, photosynthesis and dark-CO₂-fixationwere inhibited in leaf tissue from both plants. 50% inhibitionof photosynthesis in spinach occurred at about –3.0 MPa,and of dark-CO₂-fixation at about –3.5 MPa. 50% inhibitionof photosynthesis in Arbutus unedo was reached at about –4.0MPa (sorbitol as osmoticum). In both plants, osmotic dehydration decreased the slope andthe maximum of the CO₂- and light-response curves. The slopeof the CO₂-response curve of dark-CO₂-fixation was also decreasedunder hypertonic stress, but the inhibition of the maximal fixationrate was less obvious than for photosynthesis. Photosynthesis and dark-CO₂-fixation differed significantlyin their response to high temperature: under light- and CO₂-saturation,photosynthesis of spinach leaf slices had a temperature optimumat about 37 °C, and it was nearly completely inhibited at45 °C. The rate of dark-CO₂-fixation, however, increasedcontinuously up to 45 °C. Osmotic dehydration increasedthe resistance of photosynthesis to high temperatures. Key words: CO₂ response, Heat stress, Light response, Photosynthesis, Water stress     

Effect of Temperature, CO(2) Concentration, and Light Intensity on Oxygen Inhibition of Photosynthesis in Wheat Leaves

The effect of 21% O₂ and 3% O₂ on the CO₂ exchange of detached wheat leaves was measured in a closed system with an infrared carbon dioxide analyzer. Temperature was varied between 2° and 43°, CO₂ concentration between 0.000% and 0.050% and light intensity between 40 ft-c and 1000 ft-c. In most conditions, the apparent rate of photosynthesis was inhibited in 21% O₂ compared to 3% O₂. The degree of inhibition increased with increasing temperature and decreasing CO₂ concentration. Light intensity did not alter the effect of O₂ except at light intensities or CO₂ concentrations near the compensation point. At high CO₂ concentrations and low temperature, O₂ inhibition of apparent photosynthesis was absent. At 3% O₂, wheat resembled tropical grasses in possessing a high rate of photosynthesis, a temperature optimum for photosynthesis above 30°, and a CO₂ compensation point of less than 0.0005% CO₂. The effect of O₂ on apparent photosynthesis could be ascribed to a combination of stimulation of CO₂ production during photosynthesis, and inhibition of photosynthesis itself.     

CO2浓度升高对大豆冠层光合速率影响的数值模拟研究

利用美国Li-6200光合测定系统对鲁豆4号叶片光合速率进行了大量测定研究,确定了大豆叶片光-光合作用模式,模式中考虑了CO2浓度对光合作用速率的影响,在此基础上进一步测定了大豆冠层结构,建立了一个大豆冠层光合速率数值模式.利用GXH-305红外线CO2分析仪外接50×50×120cm同化箱对冠层光合速率进行了实际测定,结果表明当CO2浓度低于660ppm时,模式可以较好地模拟出CO2浓度升高对群体光合速率的影响,平均相对误差为7.41%.本文所测得的大量实验数据,为研究CO2浓度升高对大豆生长影响提供了更加可靠的模型参数,同时也为进一步建立自然状况下大豆生长数值模式提供了一定的理论依据.     

Effects of CO(2) Concentration on Rubisco Activity, Amount, and Photosynthesis in Soybean Leaves

Growth at an elevated CO₂ concentration resulted in an enhanced capacity for soybean (Glycine max L. Merr. cv Bragg) leaflet photosynthesis. Plants were grown from seed in outdoor controlled-environment chambers under natural solar irradiance. Photosynthetic rates, measured during the seed filling stage, were up to 150% greater with leaflets grown at 660 compared to 330 microliters of CO₂ per liter when measured across a range of intercellular CO₂ concentrations and irradiance. Soybean plants grown at elevated CO₂ concentrations had heavier pod weights per plant, 44% heavier with 660 compared to 330 microliters of CO₂ per liter grown plants, and also greater specific leaf weights. Ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco) activity showed no response (mean activity of 96 micromoles of CO₂ per square meter per second expressed on a leaflet area basis) to short-term (~1 hour) exposures to a range of CO₂ concentrations (110-880 microliters per liter), nor was a response of activity (mean activity of 1.01 micromoles of CO₂ per minute per milligram of protein) to growth CO₂ concentration (160-990 microliters per liter) observed. The amount of rubisco protein was constant, as growth CO₂ concentration was varied, and averaged 55% of the total leaflet soluble protein. Although CO₂ is required for activation of rubisco, results indicated that within the range of CO₂ concentrations used (110-990 microliters per liter), rubisco activity in soybean leaflets, in the light, was not regulated by CO₂.     

Effects of Elevated CO2 and High Temperature on Single Leaf and Canopy Photosynthesis of Rice

The increase of atmospheric CO2 concentration is indisputable. In such condition, photosynthetic response of leaf is relatively well studied, while the comparison of that between single leaf and whole canopy is less emphasized. The stimulation of elevated CO2 on canopy photosynthesis may be different from that on single leaf level. In this study, leaf and canopy photosynthesis of rice ( Oryza sativa L. ) were studied throughout the growing season. High CO2 and temperature had a synergetic stimulation on single leaf photosynthetic rate until grain filling. Photosynthesis of leaf was stimulated by high CO2, although the stimulation was decreased by higher temperature at grain filling stage. On the other hand, the simulation of elevated CO2 on canopy photosynthesis leveled off with time. Stimulation at canopy level disappeared by grain filling stage in beth temperature treatments. Green leaf area index was not significantly affected by CO2 at maturity, but greater in plants grown at higher temperature. Leaf nitrogen content decreased with the increase of CO2 concentration although it was not statistically significant at maturity. Canopy respiration rate increased at flowering stage indicating higher carbon loss. Shading effect caused by leaf development reached maximum at flowering stage. The CO2 stimulation on photosynthesis was greater in single leaf than in canopy. Since enhanced CO2 significantly increased biomass of rice stems and panicles, increase in canopy respiration caused diminishment of CO2 stimulation in canopy net photosynthesis, keaf nitrogen in the canopy level decreased with CO2 concentration and may eventually hasten CO2 stimulation on canopy photosynthesis. Early senescence of canopy leaves in high CO2 is also a possible cause.     

Temperature and CO2Responses of Leaf and Canopy Photosynthesis: a Clarification using the Non-rectangular Hyperbola Model of Photosynthesis

The responses of C₃leaf and canopy gross photosynthesis to increasingtemperature and CO₂can be readily understood in terms of thetemperature and CO₂dependencies of quantum yield (     

Phenotypic Plasticity Conditions the Response of Soybean Seed Yield to Elevated Atmospheric CO2 Concentration

Selection for cultivars with superior responsiveness to elevated atmospheric CO₂ concentrations (eCO₂) is a powerful option for boosting crop productivity under future eCO₂. However, neither criteria for eCO₂ responsiveness nor prescreening methods have been established. The purpose of this study was to identify traits responsible for eCO₂ responsiveness of soybean (Glycine max). We grew 12 Japanese and U.S. soybean cultivars that differed in their maturity group and determinacy under ambient CO₂ and eCO₂ for 2 years in temperature gradient chambers. CO₂ elevation significantly increased seed yield per plant, and the magnitude varied widely among the cultivars (from 0% to 62%). The yield increase was best explained by increased aboveground biomass and pod number per plant. These results suggest that the plasticity of pod production under eCO₂ results from biomass enhancement, and would therefore be a key factor in the yield response to eCO₂, a resource-rich environment. To test this hypothesis, we grew the same cultivars at low planting density, a resource-rich environment that improved the light and nutrient supplies by minimizing competition. Low planting density significantly increased seed yield per plant, and the magnitude ranged from 5% to 105% among the cultivars owing to increased biomass and pod number per plant. The yield increase due to low-density planting was significantly positively correlated with the eCO₂ response in both years. These results confirm our hypothesis and suggest that high plasticity of biomass and pod production at a low planting density reveals suitable parameters for breeding to maximize soybean yield under eCO₂.The atmospheric concentration of carbon dioxide ([CO₂]) increased from the preindustrial level of 271 µmol mol^–1 to 391 µmol mol^–1 in 2011, owing primarily to emissions from combustion of fossil fuels. [CO₂] is predicted to rise from the current level to approximately 600 µmol mol^–1 by 2050 (Ciais et al., 2013). Elevated atmospheric CO₂ concentration (eCO₂) is well known to increase leaf photosynthesis by increasing the availability of CO₂ as a substrate for the carboxylation reaction with Rubisco; this can increase crop productivity, a phenomenon known as the CO₂ fertilization effect, especially for C₃ plants such as rice (Oryza sativa), wheat (Triticum aestivum), and soybean (Glycine max; e.g. Kimball et al., 2002), since [CO₂] is a growth-limiting resource for C₃ plants. There is a large genotypic variation in the yield response to eCO₂, both among cultivars and between species, with responses ranging from –15% to +20% per 100 µmol mol^–1 CO₂ increase from the current level for rice (Ziska et al., 1996; Moya et al., 1998; Baker, 2004; Shimono et al., 2009; Hasegawa et al., 2013), –6% to +35% for wheat (Manderscheid and Weigel, 1997; Ziska et al., 2004; Ziska, 2008; Tausz-Posch et al., 2015), –5% to +55% for soybean (Ziska and Bunce, 2000; Ziska et al., 2001; Bishop et al., 2015; Bunce, 2015), and –6% to +21% for field bean (Phaseolus vulgaris; Bunce, 2008). These large differences in eCO₂ responsiveness within crop species suggest that active selection and breeding for genotypes that respond strongly to gradual but steadily increasing [CO₂] may ensure sustained productivity and improve food security in a future eCO₂ world (Ainsworth et al., 2008; Ziska et al., 2012; Tausz et al., 2013).Several hypotheses have been proposed about which traits should be targeted by breeders because they are related to intraspecific variation in the responsiveness of seed yield to eCO₂. For example, a cultivar’s maturity group is an important growth trait for determining crop productivity. Late-maturing rice cultivars as a result of the longer period in which they can grow could increase grain yield relatively by eCO₂ and may therefore benefit more from eCO₂ than early-maturing cultivars (Hasegawa et al., 2013). Also, phenological changes by eCO₂ could be another good indicator of genotypic variation in eCO₂ responsiveness. Recently, Bunce (2015) showed that extension of the duration of vegetative growth until flowering at the apical node of the main stem caused by eCO₂ was correlated with an increase in seed yield among some soybean genotypes.The source-sink relationship is another important aspect of genotypic variation in the responsiveness of a plant to eCO₂. CO₂ enrichment can increase photosynthesis, especially during the early growth stage of leaves, and the magnitude of the increase of photosynthesis decreases with increasing growth stage because leaf senescence accelerates under eCO₂, which has been referred to as acclimation (for review, see Moore et al., 1999). Genotypes with slower acclimation to eCO₂ had a greater response of seed yield (Zhu et al., 2014, for rice; Hao et al., 2012, for soybean). Determinacy is strongly related to the source-sink relationship, especially for legume species. Indeterminate soybean cultivars that have more sinks are likely to be superior in responsiveness to eCO₂, compared with determinate cultivars (Ainsworth et al., 2004). Aspinwall et al. (2015) emphasized the importance of phenotypic plasticity (the ability of a genotype to alter its phenotype in response to environmental changes) under eCO₂ as a key trait for eCO₂ responsiveness. Many researchers have suggested that a higher sink plasticity under eCO₂ would lead to greater plasticity of tillering, branching, and biomass production, and could therefore be more important than photosynthesis per unit leaf area for adaptation to eCO₂ by rice (Shimono et al., 2009; Zhu et al., 2014), soybean (Ziska and Bunce, 2000; Ziska et al., 2001), wheat (Manderscheid and Weigel, 1997; Ziska et al., 2004; Ziska, 2008), and field bean (Bunce, 2008); an exception would occur when other resources are limited, such as during a drought (Tausz-Posch et al., 2015). It is difficult to categorize biomass per se as a function of sink or source factors, but a plant’s final biomass results from efficient formation of sinks in vegetative and reproductive organs, and from efficient filling of these sinks with the products of photosynthesis. This would be a promising hypothesis, and if the hypothesis is confirmed, the phenotypic plasticity would become a useful criterion for identifying eCO₂-responsive cultivars.The first objective of the current study was to examine the genotypic variation of yield enhancement caused by eCO₂ in diverse soybean cultivars, as soybean is a major source of plant protein and oil and a major contributor to the world’s food supply. In addition to characterizing the variation, we attempted to identify the factors responsible for it. The soybean genotypes that we chose covered a wide range of maturity groups and determinacy, including near-isogenic lines. We concluded that soybean cultivars varied widely in their responsiveness to eCO₂, and that variation in the yield enhancement by eCO₂ was determined primarily by the plasticity of biomass and pod production. This suggests that both are suitable parameters for screening cultivars with a strong response to eCO₂. However, it is not easy to characterize plasticity of biomass and pod production under eCO₂ of each cultivar since CO₂ enhancement facilities such as controlled enclosed chambers are extremely expensive and not easily accessible.Our second objective was to develop a methodology to characterize intraspecific variation in plasticity. Shimono (2011) proposed a simple and novel idea: to use planting density for prescreening to identify eCO₂-responsive cultivars. Solar radiation is the driving force for photosynthesis and plant growth, and crops are grown as a population (not as individual plants) to maximize productivity per unit area rather than per plant. Individual plant growth is usually restricted by interplant competition for solar radiation, soil nutrients, and water, so a lower planting density could potentially increase the source strength for individual plants by increasing the availability of resources. Thus, lower plant density can imitate the greater resource availability that would occur under eCO₂. This approach is potentially useful but is insufficient, because Shimono et al. (2014) applied it only to rice, measured only panicle number (not yield) as the phenotype, and combined independent experimental data from different locations and years. Here, we tested the hypothesis using a diverse range of soybean cultivars at a single site and for 2 years, and found a good relationship between the responsiveness to eCO₂ and the responsiveness to low planting density (LD) in terms of the seed yield per plant.     

Response of Photosynthesis to Radiation and Intercellular CO2 Concentration in Sun and Shade Shoots of Norway Spruce

Functional differentiation of assimilation activity of sun versus shade foliage was analysed in a Norway spruce monoculture stand (age 15 years). The investigated stand density (leaf area index 8.6) and crown structure led to variation in the photosynthetically active photon flux density (PPFD) within the crowns of the sampled trees. At the saturating PPFD, the maximum rate of CO₂ uptake (P _Nmax) of exposed shoots (E-shoots) was 1.7 times that of the shaded shoots (S-shoots). The apparent quantum yield (α) of E-shoots was 0.9 times that of the S-shoots. A lower ability to use excess energy at high PPFD in photosynthesis was observed in the S-layer. The CO₂- and PPFD-saturated rate of CO₂ uptake (P _Nsat) of the E-shoots was 1.12 times and the carboxylation efficiency (τ) 1.6 times that of the S-shoots. The CO₂-saturated rate of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) carboxylation (V_Cmax) and of actual electron transport (J_amax) in the S-needles amounted to 89 and 95 % of V_Cmax and J_amax in the E-needles. Thus, in addition to the irradiation conditions and thus limitation by low J_a, the important limitation of photosynthesis in shade needles is due to carboxylation. This limitation of photosynthesis is accompanied by lower stomatal conductance. This revised version was published online in June 2006 with corrections to the Cover Date.     

Response of Photosynthesis Models to Light Limitation

An investigation into the effect of time step on a common photosynthesis algorithm reveals that the predicted phytoplankton production and biomass depend strongly on the length of the time step. This time step dependence is due to the assumption that a light limitation factor derived from integrating the irradiance over the time step is equivalent to the integrated light limitation factor over the time step. This subtle inaccuracy in defining the factor for light limited phytoplankton production produces a substantial difference in the biomass estimates derived from the two models. To illustrate the difference, the light limitation factor integrated over the time step is implemented in the one dimensional water quality model DYRESM-WQ. The new version of DYRESM-WQ is used to simulate chlorophyll N concentrations in Prospect Reservoir, New South Wales. These results are compared to concentrations predicted using the original algorithm. The comparison shows that the new algorithm for phytoplankton production is relatively insensitive to time step, which decreases the difficulty of calibrating the model for chlorophyll a.     

Control of Photosynthesis in Wheat by CO2, O2 and Light Intensity

The regulation of photosynthesis in wheat leaves under varyingO₂, CO₂, and light was studied by analyzing certain metabolitepools and enzyme activities. Under high light when the rateof photosynthesis was limited by low intercellular levels ofCO₂ (C₁) there was a high level of ribulose-1,5-bisphosphate(RuBP) (about 100 nmols per mg chlorophyll). As C, increased,there was a parallel decrease in the ratios of RuBP/3-phosphoglycerate(PGA) (from 0.18 to 0.08 under 21% O₂) and triose-phosphate/PGA(from 0.16 to 0.07 under 21% O₂). The results suggest carboxylationis limited at low C_i, and that there is high carboxylation andlimited assimilatory power at high C_i. As photosynthesis increasedwith increasing Jight intensity under atmospheric levels ofCO₂ the ratios of RuBP/PGA and triosephosphate/PGA remainednearly constant (near 0.12 to 0.13) suggesting there may bea coordinate regulation by light of the different phases ofthe cycle. There was increasing activation of ribulose 1,5-bisphosphatecarboxylase oxygenase (Rubisco) and fructose 1,6-bisphosphatase(FBPase) with increasing light intensity. The ways in whichthe light activation of the enzymes Rubisco and FBPase may regulatecarbon metabolism in the cycle are discussed. ¹ Current address: Biological Sciences Center, Desert ResearchInstitute, PO Box 60220, Reno, Nevada 89506, U.S.A. (Received March 24, 1987; Accepted June 23, 1987)     

辽东栎对大气CO2倍增的响应

 本文研究了CO2加浓对暖温带落叶阔叶混交林典型自然群落建群种辽东栎的影响,结果表明：在生理学方面,CO2倍增下气孔阻抗略增大,为对照的106％,蒸腾速率略下降,为对照的92％,暗呼吸速率与对照很接近,但略微下降为对照的98.9％。净光合速率、昼夜净光合量、水分利用效率都明显提高,分别为对照的155％,172％和179％。可以看出C02倍增对辽东栎的生理过程有促进作用,属正效应。其中以生长旺季6、7月增长更为明显。在生长方面,CO2倍增下生长各项指标增长也较明显,叶面积为对照的107％,叶干重为对照的140％,以植株高度增加最明显,为对照的331％,清楚的看出辽东栎的生长与生理过程的变化趋势是一致的、均属正效应。也就是说在其他环境资源满足植物要求时,CO2倍增对树木具有“施肥”作用,它可促进植物的生理过程和提高其生物生产力。     

Relation of CO(2) Compensation Concentration to Apparent Photosynthesis in Maize

Significant differences in CO₂ compensation concentration measured in the field among varieties of the species Zea mays L. are reported for the first time. CO₂ compensation concentrations were significantly (P≤ 0.01) and negatively correlated with apparent photosynthesis at 300 μl CO₂/liter air. The Michaelis constant (as defined) for a leaf was significantly (P≤ 0.01) and positively correlated with apparent photosynthesis among varieties. While the first correlation is similar to behavior of CO₂ compensation among species of different photosynthetic efficiency, the latter correlation is the converse of the behavior of Km among species.     

Effects of Temperature on Photosynthesis and CO(2) Evolution in Light and Darkness by Green Leaves

Using an open and a closed system of gas analysis, it was found that CO₂ evolution in light and in darkness from plant leaves (sunflower, soybean, watermelon, eggplant, and jackbean) have a different response to temperature. While the rate of CO₂ evolution in light increased with increasing temperature from 17 to 35° and then declined, the rate of CO₂ evolution in darkness increased continuously up to 40°. The rate of CO₂ evolution in light was affected by light intensity. At 1800 ft-c and below 35° the rate of CO₂ evolution in light was greater than in darkness, but above 35° it became lower than in darkness. The Q₁₀ for CO₂ evolution in light was consistently lower than that in darkness.     

Oxygen Uptake and Photosynthesis of the Red Macroalga, Chondrus crispus, in Seawater: Effects of Light and CO(2) Concentration

With an experimental system using mass spectrometry techniques and infra-red gas analysis of CO₂ developed for aquatic plants, we studied the responses to various light intensities and CO₂ concentrations of photosynthesis and O₂ uptake of the red macroalga Chondrus crispus S. The CO₂ exchange resistance at air-water interface which could limit the photosynthesis was experimentally measured. It allowed the calculation of the free dissolved CO₂ concentration. The response to light showed a small O₂ uptake (37% of net photosynthesis in standard conditions) compared to C₃ plants; it was always higher than dark respiration and probably included a photoindependent part. The response to CO₂ showed: (a) an O₂ uptake relatively insensitive to CO₂ concentration and not completely inhibited with high CO₂, (b) a general inhibition of gas exchanges below 130 microliters CO₂ per liter (gas phase), (c) an absence of an inverse relationship between O₂ and CO₂ uptakes, and (d) a low apparent K_m of photosynthesis for free CO₂ (1 micromolar). These results suggest that O₂ uptake in the light is the sum of different oxidation processes such as the glycolate pathway, the Mehler reaction, and mitochondrial respiration. The high affinity for CO₂ is discussed in relation to the use of HCO₃⁻ and/or the internal CO₂ accumulation.     

Control of the Acclimation of Photosynthesis to Light and Temperature in Relation to Partitioning of Photosynthate in Developing Soybean Leaves

Photosynthetic acclimation was examined by exposing third trifoliolateleaves of soybeans to air temperatures of 20 to 30°C andphotosynthetic photon flux densities (PPFD) of 150 to 950µmolphotons m^–2 s^–1 for the last 3 d before they reachedmaximum area. In some cases the environment of the third leafwas controlled separately from that of the rest of the plant.Photosynthesis, respiration and dry mass accumulation were determinedunder the treatment conditions, and photosynthetic capacity,and dry mass and protein content were determined at full expansion.Photosynthetic capacity, the light-saturated rate of net carbondioxide exchange at 25°C and 34 Pa external partial pressureof carbon dioxide, could be modified between 21 and 35 µmolCO₂ m^–2 s^–1 by environmental changes after leaveshad become exporters of photosynthate. Protein per unit leafmass did not differ between treatments, and photosynthetic capacityincreased with leaf mass per unit area. Photosynthetic capacityof third leaves was affected by the PPFD incident on those leaves,but not by the PPFD on other leaves on the plant. Photosyntheticcapacity of third leaves was affected by the temperature ofthe rest of the plant, but not by the temperature of the thirdleaves. Photosynthetic capacity was linearly related to carbondioxide exchange rate in the growth regimes, but not to daytimePPFD. At high PPFD, and at 25 and 30°C, mass accumulationwas about 28% of the mass of photosynthate produced. At lowerPPFD, and at 20°C, larger percentages of the photosynthateproduced accumulated as dry mass. The results suggest that photosynthatesupply is an important factor controlling leaf structural growthand, consequently, photosynthetic acclimation to light and temperature. Key words: Glycine max (L.) Merr., photosynthesis, temperature acclimation, light acclimation, photosynthate partitioning     

水稻的光合作用、生长、碳同位素分辨作用及抗渗透胁迫性对CO2浓度增高的响应

四个水稻(Oryza sativa L.)品种"IR72"、"特三矮2号"、"桂朝2号"和"Ⅱ优4480"在田间栽于含35 μmol/mol 和60 μmol/mol CO2的塑料大棚中,自然光照.高浓度CO2下供试水稻品种的光合速率变化表现为提高型("IR72"、"特三矮2号")、稳定型("桂朝2号"的Pn几无变化)和下调型("Ⅱ优4480").生长速率、穗重、由Δ13C计算而得的长期水分利用效率和清除DPPH@自由基的能力皆增加.除"Ⅱ优4480"外,其他3个品种明显增高总生物量.供试品种的穗重/总生物量比不同程度地受到高浓度CO2的改变.叶片段经PEG渗透胁迫后,不同的生长于高浓度CO2者的电解质渗漏率较小.结果表明高浓度CO2可改变水稻的光合作用和水分关系特性,品种间不同的响应显示了选育适于未来高浓度CO2下具有高产和抗逆性品种的可能性.     

Modelling Light Absorption and Canopy Net Photosynthesis of Glasshouse Row Crops and Application to Cucumber

A model of light absorption and photosynthesis applicable toglasshouse row crops is constructed and applied to cucumber.Light absorption is calculated using a method suggested fordiscontinuous canopies; photosynthesis is modelled with a non-rectangularhyperbola. The predictions of this model are compared with experimentaldata in the preceding paper. Here the model is used to simulateresponses to light and CO₂ concentration and especially to examinethe effects of varying the parameters of the crop that can becontrolled by the grower. These include the number of plantsin each row, the number and width of the rows, the gap betweenrows, and the height of the crop. For example, it is shown that,for high values of crop net photosynthesis, the number of rowsis more important at high light than at low light, whereas cropheight is more important at low light than at high light. Theimplications of these and other findings are discussed. Key words: Cucumis sativus L., glasshouse crops, cucumber, model, light absorption, photosynthesis, CO₂, row crops, simulation     

CO2浓度升高对斜生栅藻生长和光合作用的影响

升高大气中CO2 浓度可提高斜生栅藻的生物量和光合作用速率 ,对光合效率、暗呼吸速率、光饱和点和光系统Ⅱ的光化学效率 (Fv Fm)没有明显影响 ,但藻细胞光合作用对无机碳的亲和力降低     

Response of Photochemical Processes of Photosynthesis to Dinitrogen Fixation in Soybean

Symbiotic N2 fixation activity brings about changes in the photochemical processes of photosynthesis in soybean (Glycine max L. Merr.). For a potential photochemical efficiency ([phi]Po) similar to that obtained with an exclusively mineral nutrition, soybean, at full bloom stage (R2) with a moderate N2 fixation activity, had a better electron transfer quantum yield ([phi]PSII) and a higher photochemical quenching. At the beginning seed stage (R5), corresponding to more intense N2 fixation, the same phenomena were enhanced; in addition, an effect on the photochemical (k2b) and nonphotochemical (Kn-k22) transfer rates and an earlier activation of the electron transfer chain were characterized using a new parameter, the relative induction time of PSII fluorescence (Ap/Fm). The response of the photochemical parameters was related to the N2 fixation level (performance of the host plant-microsymbiont association): the energetic cost of symbiotic N2 fixation appeared to be met by a better photochemical efficiency of photosynthesis coupled with a decrease in thermal dissipation (kn - k22), by faster thylakoid energization, and by faster reopening of photosystem II centers at the time of fluorescence induction, as shown by decreased Ap/Fm.     

Gas Exchange of Carrot Leaves in Response to Elevated CO2 Concentration

Short-term responses of four carrot (Daucus carota) cultivars: Cascade, Caro Choice (CC), Oranza, and Red Core Chantenay (RCC) to CO₂ concentrations (C _a) were studied in a controlled environment. Leaf net photosynthetic rate (P _N), intercellular CO₂ (C _i), stomatal conductance (g _s), and transpiration rate (E) were measured at C _a from 50 to 1 050 mol mol^–1. The cultivars responded similarly to C _a and did not differ in all the variables measured. The P _N increased with C _a until saturation at 650 mol mol^–1 (C _i= 350–400 mol mol^–1), thereafter P _N increased slightly. On average, increasing C _a from 350 to 650 and from 350 to 1 050 mol mol^–1 increased P _N by 43 and 52 %, respectively. The P _N vs. C _i curves were fitted to a non-rectangular hyperbola model. The cultivars did not differ in the parameters estimated from the model. Carboxylation efficiencies ranged from 68 to 91 mol m^–2 s^–1 and maximum P _N were 15.50, 13.52, 13.31, and 14.96 mol m^–2 s^–1 for Cascade, CC, Oranza, and RCC, respectively. Dark respiration rate varied from 2.80 mol m^–2 s^–1 for Oranza to 3.96 mol m^–2 s^–1 for Cascade and the CO₂ compensation concentration was between 42 and 46 mol mol^–1. The g _s and E increased to a peak at C _a= 350 mol mol^–1 and then decreased by 17 and 15 %, respectively when C _a was increased to 650 mol mol^–1. An increase from 350 to 1 050 mol mol^–1 reduced g _s and E by 53 and 47 %, respectively. Changes in g _s and P _N maintained the C _i:C _a ratio. The water use efficiency increased linearly with C _a due to increases in P _N in addition to the decline in E at high C _a. Hence CO₂ enrichment increases P _N and decreases g _s, and can improve carrot productivity and water conservation.