Regulation of photosynthesis by sugars in sugarcane leaves

In sugarcane, increased sink demand has previously been shown to result in increased photosynthetic rates that are correlated with a reduction in leaf hexose concentrations. To establish whether sink limitation of photosynthesis is a result of sugar accumulation in the leaf, excision and cold-girdling techniques were used to modify leaf sugar concentrations in pot-grown sugarcane. In excised leaves that were preincubated in darkness for 3h, sucrose accumulation was reduced but accumulated again upon transfer to the light, while hexose concentrations remained lower than in controls (7.7 micromol mg(-1)FW versus 18.6 micromol mg(-1)FW hexose in controls). These results were associated with a 66% and 59% increase in photosynthetic assimilation (A) and electron transport rate (ETR), respectively, compared to controls maintained in the light. Similar increases in photosynthesis were observed when dark-treated leaves were supplied with 5mM sorbitol, but not when supplied with 5mM sucrose. Further analyses of (14)C-labeled sugars indicated rapid turnover between sucrose and hexose. Cold-girdling (5 degrees C) increased sucrose and hexose levels and resulted in a decline of photosynthetic rates over 5d (48% and 35% decline in assimilation rate and ETR, respectively). These sugar-induced changes in photosynthesis were independent of changes in stomatal conductance. This study demonstrates that the down-regulation of photosynthesis in response to culm sugar accumulation reported previously could be due to the knock-on effect of accumulation of sugar in leaf tissue, and supports the contention that hexose, rather than sucrose, is responsible for the modulation of photosynthetic activity.     

Development of C4 photosynthesis in sorghum leaves grown under free-air CO2 enrichment (FACE)

The developmental pattern of C4 expression has been well characterized in maize and other C4 plants. However, few reports have explored the possibility that the development of this pathway may be sensitive to changes in atmospheric CO2 concentrations. Therefore, both the structural and biochemical development of leaf tissue in the fifth leaf of Sorghum bicolor plants grown at elevated CO2 have been characterized. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC) activities accumulate rapidly as the leaf tissue differentiates and emerges from the surrounding whorl. Rubisco was not expressed in a cell-specific manner in the youngest tissue at the base of the leaf, but did accumulate before PEPC was detected. This suggests that the youngest leaf tissue utilizes a C3-like pathway for carbon fixation. However, this tissue was in a region of the leaf receiving very low light and so significant rates of photosynthesis were not likely. Older leaf tissue that had emerged from the surrounding whorl into full sunlight showed the normal C4 syndrome. Elevated CO2 had no effect on the cell-specific localization of Rubisco or PEPC at any stage of leaf development, and the relative ratios of Rubisco to PEPC remained constant during leaf development. However, in the oldest tissue at the tip of the leaf, the total activities of Rubisco and PEPC were decreased under elevated CO2 implying that C4 photosynthetic tissue may acclimate to growth under elevated CO2.     

Effects of changes in growth temperature on photosynthesis and carotenoid composition in Zea mays leaves

The effects of changes in growth temperature on photosynthesis and carotenoid composition were examined in Zea mays L. leaves of different age and different developmental history. The plants were first grown at sub-optimal temperature (14°C) until the full development of the third leaf. At that time, the mature third leaf and the immature fourth leaf had a low chlorophyll (Chl) content, a low Chl a/b ratio, a high carotenoid/Chl a+b ratio, a high xanthophyll/β-carotene ratio, and about 80% of the xanthophyll cycle pool (violaxanthin [V] + antheraxanthin [A] + zeaxanthin [Z]) was in the form of zeaxanthin and antheraxanthin. When the temperature was increased from 14°C to 24°C for three days, increased Chl synthesis, accompanied by an increase in the Chl a/b ratio, took place. The ratios of lutein, neoxanthin, and V+A+Z to Chl a+b decreased markedly, whereas no significant changes appeared in the β-carotene/Chl a+b ratio. Furthermore, there was a sharp decrease in the xanthophyll/β-carotene ratio and most of zeaxanthin was converted to violaxanthin in the xanthophyll cycle. The third leaf and the tip segment of the fourth leaf, both expanded at 14°C, showed little difference in their pigment contents. However, the rate of CO₂ assimilation of the tip segment of the fourth leaf was nearly twice that of the third leaf on the third day at 24°C, while the photosynthetic activity was similar in both leaves before the transfer to 24°C. During the warm period at 24°C, new leaf tissue (basal segment of the fourth leaf and part of a fifth leaf) was formed. On the third day at 24°C, the pigment content of 24°C-grown leaf tissue did not differ much from that of 14°C-grown leaf tissue with the exception that the total carotenoid content was lower in the former as compared to the latter, mainly because of a lower V+A+Z content. The rate of CO₂ assimilation of 24°C-grown leaf tissue was comparable to that of the tip segment of the fourth leaf. Regardless of which leaf tissue is considered, reducing the temperature from 24°C to 14°C for 5 days slightly affected the pigment content, but violaxanthin was largely converted to zeaxanthin and antheraxanthin in the xanthophyll cycle. The results indicate that compared to old leaf tissue of mature leaves, physiologically younger leaf tissue of immature leaves is much more able to recover from depressions in the photosynthetic activity induced by growth at sub-optimal temperature when the plants experience optimal growth temperatures, but that factors other than the pigment content must determine this capability.     

The photosynthesis of ryegrass leaves grown in a simulated sward

Plants were taken from simulated swards of perennial ryegrass (Lolium perenne) grown in a controlled environment and the rates of photosynthesis of the youngest fully expanded leaves, and the second and third youngest leaves on the same tillers were measured. The youngest leaves had the highest rates and the third the lowest, with the second leaves intermediate. The rate of photosynthesis in bright light of successive youngest expanded leaves decreased as the swards increased in leaf area, but did not when plants were grown so that the main stem was not shaded. When plants were grown at different densities and the photosynthetic rates of leaves of a particular ontogenetic rank were measured, it was found that leaves on plants from higher densities had lower rates of photosynthesis. Also leaves on plants grown in bright light had higher photosynthetic rates than those on plants grown in dim light. It is concluded that the decline in the photosynthetic capacity of successive leaves in a rapidly growing simulated sward is due to the intense shading to which they are subjected during their expansion.     

CO2加富下水氮耦合对黄瓜叶片光合作用和超微结构的影响

以‘津优35号’黄瓜为试材,采用裂区-再裂区设计,研究了CO₂加富下水氮耦合对黄瓜叶片光合作用和超微结构的影响.主区设大气CO₂浓度(400 μmol·mol^-1,A)和加富CO₂浓度(800±20 μmol·mol^-1,E)2个CO₂浓度处理,裂区设无干旱胁迫(田间持水量的95%,W)和干旱胁迫(田间持水量的75%,D)2个水分处理,再裂区设施氮量450 kg·hm^-2(低氮,N₁)和900 kg·hm^-2(高氮,N₂)2个氮素处理.结果表明: 在干旱和高氮条件下,CO₂加富提高了黄瓜的株高,且使高氮下的叶面积显著增加.正常灌溉条件下,高氮处理的光合速率、气孔导度和蒸腾速率高于低氮处理,而干旱条件下则相反;CO₂加富提高了黄瓜叶片的水分利用效率,并且随着施氮量的增加,其水分利用效率提高.干旱胁迫下,黄瓜近轴面气孔密度增加,而CO₂加富和高氮却显著降低了气孔密度.高氮处理增加了黄瓜叶片叶绿体数量而减少了淀粉粒数量,干旱胁迫使叶绿体数量减少,但使淀粉粒数量呈上升趋势.干旱胁迫增加了叶绿体长度和宽度,显著增加了淀粉粒的大小,而高氮降低了叶绿体和淀粉粒的长度和宽度.CO₂加富和高氮均使基粒厚度和片层数增加(ADN₂除外),并且EDN₂处理的片层数显著高于ADN₂.综上所述,CO₂加富和适宜的水、氮条件能促进黄瓜叶片叶绿体类囊体膜系的发育,显著增加基粒厚度和基粒片层数,有效改善黄瓜的叶绿体结构,增强光合性能,提高黄瓜植株对CO₂和水、氮的吸收利用能力.     

Lateral diffusion of CO2 in leaves is not sufficient to support photosynthesis

Lateral diffusion of CO(2) was investigated in photosynthesizing leaves with different anatomy by gas exchange and chlorophyll a fluorescence imaging using grease to block stomata. When one-half of the leaf surface of the heterobaric species Helianthus annuus was covered by 4-mm-diameter patches of grease, the response of net CO(2) assimilation rate (A) to intercellular CO(2) concentration (C(i)) indicated that higher ambient CO(2) concentrations (C(a)) caused only limited lateral diffusion into the greased areas. When single 4-mm patches were applied to leaves of heterobaric Phaseolus vulgaris and homobaric Commelina communis, chlorophyll a fluorescence images showed dramatic declines in the quantum efficiency of photosystem II electron transport (measured as F(q)'/F(m)') across the patch, demonstrating that lateral CO(2) diffusion could not support A. The F(q)'/F(m)' values were used to compute images of C(i) across patches, and their dependence on C(a) was assessed. At high C(a), the patch effect was less in C. communis than P. vulgaris. A finite-volume porous-medium model for assimilation rate and lateral CO(2) diffusion was developed to analyze the patch images. The model estimated that the effective lateral CO(2) diffusion coefficients inside C. communis and P. vulgaris leaves were 22% and 12% of that for free air, respectively. We conclude that, in the light, lateral CO(2) diffusion cannot support appreciable photosynthesis over distances of more than approximately 0.3 mm in normal leaves, irrespective of the presence or absence of bundle sheath extensions, because of the CO(2) assimilation by cells along the diffusion pathway.     

供氮和增温对倍增二氧化碳浓度下荫香叶片光合作用的影响

供给0～0.6 mg N的盆栽荫香(Cinnamomum burmannii)幼树分别生长在倍增CO ₂(+CO₂,731 μmol·mol^-1)和正常空气CO ₂浓度(CO ₂,365 μmol·mol^-1)的生长箱内,昼夜温度分别为25/23 ℃和32/25 ℃,自然光照下生长30 d.以生长在CO₂和25/23 ℃下的植株为对照研究增温和氮对+CO₂叶片光合作用的影响.结果表明,在+CO₂和25/23 ℃下无氮和氮处理植株的平均光合速率(Pnsat)较+CO₂和32/25 ℃下的叶片高5.1%,温度增高降低叶片Pnsat;而Pnsat随供氮而增高.在+CO₂条件下,生长在32/25 ℃下的叶片Rubisco最大羧化速率(Vcmax)和最大电子传递速率(Jmax)较25/23 ℃下的低(P＜0.05),温度增高降低+CO₂下叶片的Vcmax和Jmax在+CO2下叶片光合呼吸速率(Rp)较低,生长温度增高提升Rp.在CO₂下生长温度从25/23 ℃增至32/25 ℃,叶片的Rubisco含量(NR)和Rubisco活化中心浓度(M)降低,而供氮能增高NR和M.供氮能减缓温度增高对倍增CO₂下荫香叶片光合作用的限制.     

Rates of glycolate synthesis and metabolism during photosynthesis of Euglena and microalgae grown on low CO2

The rate of glycolate excretion in Euglena gracilis Z and some microalgae grown at the atmospheric level of CO₂ was determined using amino-oxyacetate (AOA). The extracellular O₂ concentration was kept at 240 M by bubbling the incubation medium with air. Glycolate, the main excretion product, was excreted by Euglena at 6 mol·h^-1·(mg chlorophyll (Chl))^-1. Excretion depended on the presence of AOA, and was saturated at 1 mM AOA. A substituted oxime formed from glyoxylate and AOA was also excreted. Bicarbonate added at 0.1 mM did not prevent the excretion of glycolate. The excretion of glycolate increased with higher O₂ concentrations in the medium, and was competitively inhibited by much higher concentrations of bicarbonate. Aminooxyacetate also caused excretion of glycolate from the green algae, Chlorella pyrenoidosa, Scenedesmus obliquus and Chlamydomonas reinhardtii grown on air, at the rates of 2–7 mol·h^-1·(mg Chl)^-1 in the presence of 0.2–0.6 mM dissolved inorganic carbon, but the cyanobacterium, Anacystis nidulans, grown in the same way did not excrete glycolate. The efficiency of the CO₂-concentrating mechanism to suppress glycolate formation is discussed on the basis of the magnitude of glycolate formation in these low-CO₂-grown cells.Abbreviations AOA aminooxyacetate - Chl chlorophyll - DIC dissolved inorganic carbon - HPLC high-pressure liquid chromatography - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase This is the 16th paper in a series on the metabolism of glycolate in Euglena gracilis. The 15th paper is Yokota et al. (1985c)     

温度和CO2浓度升高对荒漠藻结皮光合作用的影响

2007年,对腾格里沙漠东南缘沙坡头地区1956年(51龄)和1981年(26龄)人工植被区及自然植被区的藻结皮净光合速率(P_n)变化,及其与结皮含水量(>100%、40%～60%和<20%)、大气CO₂浓度(360和700 mg·L^-1)和温度(13 ℃、24 ℃ 和28 ℃)的关系进行研究.结果表明：51龄、26龄人工植被区和自然植被区的藻结皮P_n分别为3.4、4.4和3.2 μmol·m^-2·s^-1,且51龄人工植被区藻结皮的P_n显著高于26龄人工植被区和自然植被区;藻结皮含水量对其P_n影响显著,且中等含水量(40%～60%)藻结皮的P_n显著高于低含水量(<20%)和高含水量(>100%);CO₂倍增(700 mg·L^-1)后,中等和高含水量藻结皮的P_n增加了1.8～3.3倍,而低含水量时,藻结皮的P_n变化不明显;高含水量和中等含水量处理时,24 ℃和28 ℃条件下藻结皮的P_n较13 ℃时提高27%～66%,而在低含水量时,不同温度的藻结皮P_n值无显著差异.     

水稻叶片光合作用对开放式空气CO2浓度增高(FACE)的响应与适应

利用便携式光合气体分析系统 (LI 6 4 0 0 ) ,比较测定了高CO2 浓度 (FACE ,free airCO2 enrich ment)和普通空气CO2 浓度下生长的水稻叶片的净光合速率、水分利用率、表观量子效率和RuBP羧化效率等光合参数 .在各自生长CO2 浓度 (380vs 5 80 μmol·mol-1)下测定时 ,高CO2 浓度 (5 80 μmol·mol-1)下生长的水稻叶片的净光合速率、碳同化的表观量子效率和水分利用率明显高于普通空气 (380 μmol·mol-1)下生长的水稻叶片 .但是 ,随着FACE处理时间的延长 ,高CO2 浓度对净光合速率的促进作用逐渐减小 .在相同CO2 浓度下测定时 ,FACE条件下生长的水稻叶片净光合速率和羧化效率明显比普通空气下生长的对照低 .尽管高CO2 浓度下生长的水稻叶片的气孔导度明显低于普通空气中生长的水稻叶片 ,但两者胞间CO2 浓度差异不显著 ,因此高CO2 浓度下生长的水稻叶片光合下调似乎不是由气孔导度降低造成的 .     

Influence of CO2 and sucrose on photosynthesis and transpiration of Actinidia deliciosa explants cultured in vitro

Explants of Actinidia deliciosa Chev. Liang and Ferguson var. Hayward were cultured in controlled CO2 atmospheres in the presence of different sucrose concentrations. Organogenesis was measured after 45 days in explants from the different assays, and quantification of photosynthesis, transpiration, chlorophylls, RUBISCO and total soluble protein content was performed in leaves from the different treatments. The best results were those of explants cultured at 600 &mgr;mol CO2 mol-1 on 20 g l-1 of sucrose for the first 20 days and then transferred to sucrose-free medium until the end of the culture period. Increasing CO2 to 2000 &mgr;mol CO2 mol-1 in the atmosphere of the culture vessel reduced all the parameters studied. Photosynthesis of autotrophically developed explants trebled that of the reference heterotrophic explants, as there was an apparent inverse relationship between photosynthesis and transpiration. Photosynthesis was saturated at 300 &mgr;mol m-2 s-1 PPFD and 600 &mgr;mol CO2 mol-1. Chlorophylls and RUBISCO presented differences between treatments, mainly between different CO2 concentrations, with the highest values in autotrophically cultured explants. Explants grown at 2000 &mgr;mol CO2 mol-1 showed the lowest RUBISCO/Prots ratio, probably due to negative adaptation of RUBISCO to long-term high CO2. In short, explants grown in a controlled microenvironment, with increased CO2 and under autotrophic conditions, developed wholly functional photosynthetic apparatus well prepared to be transferred to ex vitro conditions, which has many advantages in micropropagation.     

Effects of elevated CO2 concentration and climate-warming on photosynthesis during winter in Lolium perenne

Long-term effects of atmospheric carbon dioxide concentration(ambient or 700 µmol mol^–1) and air temperature(simulation of field conditions or + 4 C) on leaf photosyntheticrate were examined in Lolium perenne L. cv. Vigor, exposed tonatural illumination during winter. Photosynthetic capacitywas compared over a range of air temperatures and photon fluxdensities of photosynthetically active radiation which wererepresentative of winter climate (5–15 C and 0–500µmol m^–2s^–1), with CO₂ level during measurementsimilar to that during the experimental period. Long-term exposureto increased air temperature reduced leaf CO₂ fixation capacityby 23% (averaged over all measurement conditions), resultingfrom a decline in lightsaturated uptake rate, but not in incident-lightquantum efficiency. CO₂- stimulation was largely absent in plantsgrown in ambient temperature, but pronounced in plants grownunder +4 C, where it compensated for two-thirds of the 23%drop. This enhancing effect of elevated CO₂ level on leaf CO₂uptake rate observed in the warmer treatment, was strongly dependenton measurement temperature, increasing from 5% at 5 C, to upto 32% at 15 C. Measurements of chlorophyll fluorescence anddry matter corresponded with the observed changes in assimilationcapacity, which could not be attributed to a deteriorated nitrogenstatus of the leaves as there was a similar N content on anarea basis. Several hypotheses are considered to explain theobserved CO₂-temperature interactions. Key words: Acclimation, chlorophyll fluorescence, elevated CO₂ level, global warming, low temperature     

Effects of red and blue light on the composition and morphology of maize kernels grown in vitro

Growth and development of plants are known to be affected by exposure to red and blue light. Mechanisms by which light quality influences gene expression in maize (Zea mays L.) embryos have not been explored. Maize kernels can be cultured in vitro allowing experimental manipulation of environmental factors during seed development. We used the in vitro kernel culture system to investigate the response of developing maize seeds, which normally develop without exposure to light, to controlled light quality. Kernels grown under red light accumulated more dry weight than those grown in darkness, whereas kernels grown under blue light accumulated less. Reciprocal color shift experiments showed that light quality during the first week in culture had more influence on kernel weight than during the subsequent three weeks in culture. Soluble sugars were higher in both light treatments than in darkness. Blue-grown kernels had higher amino acid and lower lipid levels than red-or dark-grown kernels. Embryo morphology was markedly affected by red light, under which the upper shoot axis was longer than under blue light or in darkness. Embryo morphology was influenced by light quality during the later stages of development rather than the first week. We suggest, based on these results, that gene expression in the embryo and endosperm of developing maize seeds is sensitive to light quality, and the mechanism and time dependence of this effect warrant further study. In vitro maize kernel culture affords a convenient system for such light quality experiments.     

臭氧和气溶胶复合污染对杨树叶片光合作用的影响

由于经济的快速发展, 中国大部分地区正面临着严峻的复合型大气污染, 其中臭氧和气溶胶是两种主要污染物。已有的研究表明臭氧对叶片的氧化性伤害能够抑制光合作用, 而气溶胶可通过增加散射辐射比例或缓解高温抑制促进光合作用。但复合污染下, 臭氧和气溶胶如何共同调控叶片光合作用, 仍缺乏研究。该研究利用北京及周边地区之间的污染梯度, 选择加杨(Populus × canadensis)作为实验对象, 于2012-2013年生长季期间对叶片光合速率进行连续观测, 并同时监测臭氧浓度(AOT40)、气溶胶光学厚度(AOD)、空气温度和冠层内外光合有效辐射(PAR)等环境因子, 以期探讨大气复合污染下臭氧和气溶胶变化对植物叶片光合作用的影响及相关机制。结果表明: (1)臭氧浓度与空气温度、气溶胶浓度之间均呈显著正相关关系, 但气溶胶浓度与空气温度没有显著相关关系; (2)臭氧浓度增加显著抑制了阳生叶片的光合作用, 但气溶胶浓度上升促进了阳生叶片的光合作用; 臭氧浓度升高对阴生叶片光合作用的影响较小, 但气溶胶浓度上升促进了阴生叶片的光合作用; (3)标准化后的结果显示, 臭氧对阳生叶片光合作用的影响最大, 此时气溶胶的促进作用一定程度上补偿了臭氧浓度上升所带来的抑制效应。对于阴生叶片光合作用而言, 气溶胶则是最重要的影响因素。该研究发现复合污染下阴生叶和阳生叶光合响应不同, 这表明冠层结构可能通过影响阴生叶和阳生叶的比例, 从而对植物生长产生不同影响。该研究对理解大气复合污染如何影响光合作用提供了的机理支持, 同时也表明, 为了维持生态系统生产力及功能, 需要同时控制气溶胶和臭氧污染。     

Effects of nitrogen supply on the acclimation of photosynthesis to elevated CO2

A common observation in plants grown in elevated CO₂ concentration is that the rate of photosynthesis is lower than expected from the dependence of photosynthesis upon CO₂ concentration in single leaves of plants grown at present CO₂ concentration. Furthermore, it has been suggested that this apparent down regulation of photosynthesis may be larger in leaves of plants at low nitrogen supply than at higher nitrogen supply. However, the available data are rather limited and contradictory. In this paper, particular attention is drawn to the way in which whole plant growth response to N supply constitutes a variable sink strength for carbohydrate usage and how this may affect photosynthesis. The need for further studies of the acclimation of photosynthesis at elevated CO₂ in leaves of plants whose N supply has resulted in well-defined growth rate and sink activity is emphasised, and brief consideration is made of how this might be achieved.Abbreviations A rate of CO₂ assimilation - C_i internal CO₂ concentration - PCR photosynthetic carbon reduction - Rubisco Ribulose 1,5-bisphosphate carboxylase/oxygenase - RuBP ribulose 1,5-bisphosphate     

水分对番茄不同叶龄叶片光合作用的影响

以番茄品种"金棚1号"为材料,采用盆栽方式,按照蒸腾蒸发量(ET)的50%、75%、100%和125%作为补充灌溉量研究了不同水分下番茄结果期叶片气体交换特性和光响应特征参数随叶龄的变化。结果表明:番茄叶片随着叶龄的增加,净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)逐渐降低,水分利用效率(WUE)呈先上升后下降趋势;叶龄为18 d和29 d的叶片最大净光合速率(Pmax)随灌溉量的增加均先增加后降低,分别在75%ET和100%ET处理达到最大值。叶龄为38 d和47 d的叶片Pmax均以125%ET处理最大。表观量子效率(α)随叶龄的增大也先升高后下降,在叶龄为38 d时最大;番茄叶片的光饱和点(LSP)随叶龄的加大而减小。不同水分处理下不同叶龄叶片的光响应特征参数为:叶片在叶龄为18 d时,Pmax为20.64—26.73μmol.m-.2s-1,α为0.0518—0.0556;叶龄为29 d时,Pmax为11.00—24.24μmol.m-.2s-1,α为0.0522—0.0594;叶龄为38 d时,Pmax为11.77—18.18μmol.m-.2s-1,α为0.0619—0.0693;叶龄为47 d时,Pmax为9.09—18.17μmol.m-.2s-1,α为0.0538—0.0606。随叶龄加大,增加补充灌溉量有利于延缓叶片光合能力的降低。气孔限制是水分影响番茄叶片光合作用的主要因素,气孔限制与非气孔限制因素是番茄叶片Pn随叶龄变化的原因。     

Effects of ozone and aerosol pollution on photosynthesis of poplar leaves

由于经济的快速发展, 中国大部分地区正面临着严峻的复合型大气污染, 其中臭氧和气溶胶是两种主要污染物。已有的研究表明臭氧对叶片的氧化性伤害能够抑制光合作用, 而气溶胶可通过增加散射辐射比例或缓解高温抑制促进光合作用。但复合污染下, 臭氧和气溶胶如何共同调控叶片光合作用, 仍缺乏研究。该研究利用北京及周边地区之间的污染梯度, 选择加杨(Populus × canadensis)作为实验对象, 于2012-2013年生长季期间对叶片光合速率进行连续观测, 并同时监测臭氧浓度(AOT40)、气溶胶光学厚度(AOD)、空气温度和冠层内外光合有效辐射(PAR)等环境因子, 以期探讨大气复合污染下臭氧和气溶胶变化对植物叶片光合作用的影响及相关机制。结果表明: (1)臭氧浓度与空气温度、气溶胶浓度之间均呈显著正相关关系, 但气溶胶浓度与空气温度没有显著相关关系; (2)臭氧浓度增加显著抑制了阳生叶片的光合作用, 但气溶胶浓度上升促进了阳生叶片的光合作用; 臭氧浓度升高对阴生叶片光合作用的影响较小, 但气溶胶浓度上升促进了阴生叶片的光合作用; (3)标准化后的结果显示, 臭氧对阳生叶片光合作用的影响最大, 此时气溶胶的促进作用一定程度上补偿了臭氧浓度上升所带来的抑制效应。对于阴生叶片光合作用而言, 气溶胶则是最重要的影响因素。该研究发现复合污染下阴生叶和阳生叶光合响应不同, 这表明冠层结构可能通过影响阴生叶和阳生叶的比例, 从而对植物生长产生不同影响。该研究对理解大气复合污染如何影响光合作用提供了的机理支持, 同时也表明, 为了维持生态系统生产力及功能, 需要同时控制气溶胶和臭氧污染。     

Specification of adaxial and abaxial stomata, epidermal structure and photosynthesis to CO2 enrichment in maize leaves

Acclimation to CO2 enrichment was studied in maize plants grown to maturity in either 350 or 700 microl l-1 CO2. Plants grown with CO2 enrichment were significantly taller than those grown at 350 microl l-1 CO2 but they had the same number of leaves. High CO2 concentration led to a marked decrease in whole leaf chlorophyll and protein. The ratio of stomata on the adaxial and abaxial leaf surfaces was similar in all growth conditions, but the stomatal index was considerably increased in plants grown at 700 microl l-1 CO2. Doubling the atmospheric CO2 content altered epidermal cell size leading to fewer, much larger cells on both leaf surfaces. The photosynthesis and transpiration rates were always higher on the abaxial surface than the adaxial surface. CO2 uptake rates increased as atmospheric CO2 was increased up to the growth concentrations on both leaf surfaces. Above these values, CO2 uptake on the abaxial surface was either stable or increased as CO2 concentration increased. In marked contrast, CO2 uptake rates on the adaxial surface were progressively inhibited at concentrations above the growth CO2 value, whether light was supplied directly to this or the abaxial surface. These results show that maize leaves adjust their stomatal densities through changes in epidermal cell numbers rather than stomatal numbers. Moreover, the CO2-response curve of photosynthesis on the adaxial surface is specifically determined by growth CO2 abundance and tracks transpiration. Conversely, photosynthesis on the abaxial surface is largely independent of CO2 concentration and rather independent of stomatal function.     

CO2浓度升高对干旱胁迫下小麦光合作用和抗氧化酶活性的影响

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Effects of atmospheric CO2 enrichment and foliar methanol application on net photosynthesis of sour orange tree (Citrus aurantium; Rutaceae) leaves

Foliar spray applications of 40% aqueous methanol were made to sunlit leaves of sour orange trees that had been grown continuously in clear-plastic-wall open-top enclosures maintained out-of-doors at Phoenix, Arizona, for over 5.5 years in ambient air of approximately 400 μmol mol^-1 CO₂ and in air enriched with CO₂ to a concentration of approximately 700 μmol mol^-1. No unambiguous effects of the methanol applications were detected in net photosynthesis measurements made on foliage in either of the two CO₂ treatments. The 75% increase in CO₂, however, raised the upper-limiting leaf temperature for positive net photosynthesis by approximately 7 C, which resulted in a 75% enhancement in net photosynthesis at a leaf temperature of 31 C, a 100% enhancement at a leaf temperature of 35 C, and a 200% enhancement at 42 C.