首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 671 毫秒
1.
Measurements of soluble protein levels and catalytic capacity (maximum extractable activity) of isocitrate, glucose-6-phosphate and glutamate dehydrogenases were performed in needles of Picea abies L. Karst. under phytotron-controlled conditions in filtered or SO2 polluted (0.08 ppm, 3.1 μmol m−3) air. In watered plants, pollution had no significant effects, although sulphur accumulated in the needles. Water deprivation (1 or 2 weeks depending on the experiments) of non-polluted plants decreased protein concentration and modified enzyme capacity, particularly for isocitrate and glucose-6-phosphate dehydrogenases. These effects were amplified in the polluted plants. Visible damage occurred only in plants subjected to both pollution and water stress. The results indicate that in spruce needles vulnerability of cell metabolism to the effects of a drought period is increased when water deprivation occurs under SO2 pollution.  相似文献   

2.
To elucidate how excess light energy is dissipated during water deficit, net photosynthesis (PN), stomatal conductance (gs), intercellular CO2 concentration (ci) and Chl a fluorescence were investigated in control and drought-stressed tomato plants ( Lycopersicon esculentum ). Gross O2 evolution (Eo) and gross O2 uptake (Uo) were determined by a mass spectrometric 16O/18O2 isotope technique. Under drought stress PN, gs, ci and Uo decline. While photochemical fluorescence quenching decreases under water deficit, non-photochemical quenching rises. The maximal efficiency of PSII measured in the dark is not affected by drought; however, in the light, Eo decreases under water deficit. The ratio PN/Eo falls under stress while the ratio Uo/Eo increases. We conclude that tomato plants follow a double strategy to avoid photodamage under drought stress conditions: (1) a substantial portion of light energy is emitted as heat and PSII activity is downregulated. This results in a decrease in Eo as well as PN and Uo. Despite reduced charge separation at PSII, the decline of CO2 assimilation because of lowered stomatal conductance and metabolic changes results in the need of degrading excessive photosynthetic electrons. (2) Oxygen is used as an alternative electron acceptor in photorespiration or Mehler reaction and Uo rises relative to Eo.  相似文献   

3.
Effects of water deficit on photosynthetic capacity   总被引:11,自引:0,他引:11  
Under drought, CO2 assimilation rates decrease already at small leaf water deficits. At least part of the inhibition is attributed to non-stomata1 effects at the chloroplast level, with electron transport and phosphorylation being main targets of inhibition. These findings are questioned by direct measurements of photosynthetic capacity with systems that are not Limited by stomata, e.g. leaf slices in solution or leaves at ex-ternal CO2 concentrations exceeding 5%. Here, photosynthesis was rather insensitive to dehydration down to 50–70% relative water content, and different plant species re-sponded in a very similar way. More severe dehydration affected not only pboto-synthesis, but also dark CO2 fixation and presumably also photorespiration. Rever-sible and unspecific inhibition is thought to be mediated mainly by increased concen-trations of solutes in dehydrated cells. Inhibition of photorespiration might favour photoinhibition when long-term water stress is coupled with full sunlight. Photo-inhibition, together with general senescence phenomena might be involved in long-term effects of water stress under natural drought conditions. This offers an explanation for the conflicting results of short-term water stress experiments and studies carried out under field conditions.  相似文献   

4.
Plants grown in an environment of elevated CO2 and temperature often show reduced CO2 assimilation capacity, providing evidence of photosynthetic downregulation. The aim of this study was to analyse the downregulation of photosynthesis in elevated CO2 (700 µmol mol−1) in nodulated alfalfa plants grown at different temperatures (ambient and ambient + 4°C) and water availability regimes in temperature gradient tunnels. When the measurements were taken in growth conditions, a combination of elevated CO2 and temperature enhanced the photosynthetic rate; however, when they were carried out at the same CO2 concentration (350 and 700 µmol mol−1), elevated CO2 induced photosynthetic downregulation, regardless of temperature and drought. Intercellular CO2 concentration measurements revealed that photosynthetic acclimation could not be accounted for by stomatal limitations. Downregulation of plants grown in elevated CO2 was a consequence of decreased carboxylation efficiency as a result of reduced rubisco activity and protein content; in plants grown at ambient temperature, downregulation was also induced by decreased quantum efficiency. The decrease in rubisco activity was associated with carbohydrate accumulation and depleted nitrogen availability. The root nodules were not sufficiently effective to balance the source–sink relation in elevated CO2 treatments and to provide the required nitrogen to counteract photosynthetic acclimation.  相似文献   

5.
The effects of fluridone on guard cell morphology, chloroplast ultrastructure and accumulation of drought stress-induced abscisic acid (ABA) were studied in Vicia faba L. plants grown under different light conditions. Drought stress was induced by allowing the leaves to lose 12% of their fresh weight. The appearance of defective and undeveloped stomata, and chloroplasts with a destroyed thylakoid membrane system was found in fluridone-treated plants grown at a photosynthetic photon flux (PPF) of 600 μmol m-2 s-1. Plants grown at a PPF of 40 μmol m-2 s-1 had diminished levels of ABA after imposition of dehydration. Fluridone treatment reduced the level of ABA in both unstressed and dehydrated leaves. Accumulation of ABA in the control plants was considerably reduced when they were exposed to dark periods of 24, 48 and 72 h just before imposition of the stress. Twenty-four hours after the dark treatment dehydration of the leaves resulted in a 3-fold decrease in the level of stress-induced ABA, and 72 h after dark treatment the amount of stress-induced ABA approximated the prestressed values. Fluridone-treated plants failed to accumulate ABA under water stress. In addition to functionally active chloroplasts, well-developed and functional stomata are required for drought stress to elicit a rise in ABA.  相似文献   

6.
The CO2-concentrating mechanism present in C4 plants decreases the oxygenase activity of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) and, consequently, photorespiratory rates in air. Under drought conditions, the intercellular CO2 concentration may decrease and cause photorespiration to increase. The C4 grasses Paspalum dilatatum Poiret, Cynodon dactylon (L.) Pers. and Zoysia japonica Steudel were grown in soil and drought was imposed by ceasing to provide water. Net CO2 assimilation ( A ) and stomatal conductance to water vapour decreased with leaf dehydration. Decreased carbon and increased oxygen isotope composition were also observed under drought. The response of A to CO2 suggested that the compensation point was zero in all species irrespective of the extent of drought stress. A slight decrease of A as O2 concentration increased above 10% provided evidence for slow photorespiratory gas exchanges. Analysis of amino acids contained in the leaves, particularly the decrease of glycine after 30 s in darkness, supported the presence of slow photorespiration rates, but these were slightly faster in Cynodon dactylon than in Paspalum dilatatum and Zoysia japonica . Although the contents of glycine and serine increased with dehydration and mechanistic modelling of C4 photosynthesis suggested slightly increased photorespiration rates in proportion to photosynthesis, the results provide evidence that photorespiration remained slow under drought conditions.  相似文献   

7.
The regional abundance of C4 grasses is strongly controlled by temperature, however, the role of precipitation is less clear. Progress in elucidating the direct effects of photosynthetic pathway on these climate relationships is hindered by the significant genetic divergence between major C3 and C4 grass lineages. We addressed this problem by examining seasonal climate responses of photosynthesis in Alloteropsis semialata , a unique grass species with both C3 and C4 subspecies. Experimental manipulation of rainfall in a common garden in South Africa tested the hypotheses that: (1) photosynthesis is greater in the C4 than C3 subspecies under high summer temperatures, but this pattern is reversed at low winter temperatures; and (2) the photosynthetic advantage of C4 plants is enhanced during drought events. Measurements of leaf gas exchange over 2 years showed a significant photosynthetic advantage for the C4 subspecies under irrigated conditions from spring through autumn. However, the C4 leaves were killed by winter frost, while photosynthesis continued in the C3 plants. Unexpectedly, the C4 subspecies also lost its photosynthetic advantage during natural drought events, despite greater water-use efficiency under irrigated conditions. This study highlights previously unrecognized roles for climatic extremes in determining the ecological success of C3 and C4 grasses.  相似文献   

8.
The effect of temperature and humidity on SO2–induced photosynthetic depression was determined in gas exchange experiments with leaves of Vicia faba , L. Stomatal behaviour was sensitive to humidity resulting in higher uptake rates of SO2 and stronger reductions of photosynthesis at low VPD (vapour pressure deficit). After a fumigation period of 2 h, when the photosynthetic rate had stabilized, photosynthesis of leaves exposed to SO2 at 8°C was reduced much more than at 18°C at the same rate of SO2 uptake. Data analysis with a mechanistic model revealed that this effect was due to the slower rate of S(IV) oxidation at lower temperatures, resulting in higher accumulation of S(IV) and thus stronger reduction of photosynthesis. These results were confirmed by experimental analyses of the S(IV) concentration in leaves following fumigation, which showed that more S(IV) accumulated in leaves exposed at a lower temperature. This may explain the high sensitivity of plants exposed to SO2 under winter conditions, when both VPD and temperature are low.  相似文献   

9.
Abstract. The objective of this study was to investigate the effects of water stress in sweet potato ( Ipomoea batatas L. [Lam] 'Georgia Jet') on biomass production and plant-water relationships in an enriched CO2 atmosphere. Plants were grown in pots containing sandy loam soil (Typic Paleudult) at two concentrations of elevated CO2 and two water regimes in open-top field chambers. During the first 12 d of water stress, leaf xylem potentials were higher in plants grown in a CO2 concentration of 438 and 666 μmol mol−1 than in plants grown at 364 μmol mol−1. The 364 μmol mol−1 CO2 grown plants had to be rewatered 2 d earlier than the high CO2-grown plants in response to water stress. For plants grown under water stress, the yield of storage roots and root: shoot ratio were greater at high CO2 than at 364 μmol mol−1; the increase, however, was not linear with increasing CO2 concentrations. In well-watered plants, biomass production and storage root yield increased at elevated CO2, and these were greater as compared to water-stressed plants grown at the same CO2 concentration.  相似文献   

10.
A simple method is proposed for quantitative evaluation of Stomatal and non-stomatal components of the decline in leaf CO2 uptake during rapid water stress. The changes in leaf conductance were measured during the stress and were used to calculate the photosynthetic rate which would be observed if Stomatal closure were the only cause of the decline in photosynthesis. Photosynthesis-CO2 response curves, determined just before the stress, were used for this calculation. The difference between the calculated and the actual rate is a measure of the non-stomatal effect of water stress.
This analysis was tested on Sinapis alba submitted to rapid and severe water stress by excising leaves or roots. Experiments were performed at saturating light conditions under high (61 Pa), normal (34 Pa) or low (11 Pa) ambient CO 2 pressure. The non-stomatal effect on de-rooted plants reaches a maximum at the beginning of the stress and is dependent on the CO 2 pressure: after 45 min its influence is still about 100°, 70° and 8°, respectively, at high, normal and low CO2. In the excised leaf system in which desiccation was more rapid, the non-stomatal effect accounted for nearly 100° of the assimilation decline whatever the CO2 pressure.  相似文献   

11.
The interaction of CO2 enrichment and drought on water status and growth of pea plants was investigated. Pisum sativum L. (cv. Alaska) plants were grown from seeds in growth chambers using 350 and 675 μl I1 CO2, a photon flux density of 600 μmol M-2 S-1, a 16 h photoperiod and a temperature regime of 20/14°C. The drought treatment was started at the beginning of branch initiation and lasted for 9 or 11 days. The water status of the plants was monitored daily by measuring total leaf water potential and stomatal conductance. The total leaf water potential of well-watered plants was not affected by the CO2 level. Under draughting conditions total leaf water potential decreased, with a slower decrease under the high CO2 regime, due, at least in part, to reduced stomatal conductance. Upon rewatering, total leaf water potential and stomatal conductance recovered within one day. High CO2 counteracted the reduction in height and, to some extent, leaf area that developed in low CO2 unwatered plants. Additional CO2 had no effect on branch number and did not prevent the complete inhibition of branch development that resulted from drought stress. Removing the drought conditions resulted in a rapid recovery of the internal water status and also a rapid recovery of most, but not all, plant growth parameters.  相似文献   

12.
The immission-response effect of five low levels of sulfur dioxide on net photosynthesis and transpiration was studied during continuous measurements in near-complete life cycles of whole bean plants ( Phaseolus vulgaris L. cv. Processer) grown in a controlled environment. Sixteen plants were grown in individual water cultures in each of five 100 1 glass assimilation chambers with a new type of exposure system with separate root aeration. SO2 immission ranged from 10 μg m−3 to 950 μg m−3 during 12-h day-time exposure periods, five days a week, while a low, natural background of NOx was accepted.
The SO2-induced photosynthetic reductions were in the short term, but in particular on the long-term level very closely related with stomatal conductance (significance level better than 0.0005). However, a causal coherence was not inferred. Physiological inhibitions were composed of: (1) A reversible component (night and week-end recovery) and (2) an irreversible component (related to reduced green leaf area). The pattern of leaf growth was studied, with the conclusion that SO2 reduced leaf area by promoting senescence, rather than by interfering with leaf emergence and development.  相似文献   

13.
Plant responses to elevated CO2 can be modified by many environmental factors, but very little attention has been paid to the interaction between CO2 and changes in vapour pressure deficit (VPD). Thirty-day-old alfalfa plants ( Medicago sativa L. cv. Aragón), which were inoculated with Sinorhizobium meliloti 102F78 strain, were grown for 1 month in controlled environment chambers at 25/15°C, 14 h photoperiod, and 600 µmol m−2 s−1 photosynthetic photon flux (PPF), using a factorial combination of CO2 concentration (400 µmol mol−1 or 700 µmol mol−1) and vapour pressure deficit (0.48 kPa or 1.74 kPa, which corresponded to relative humidities of 85% and 45% at 25°C, respectively). Elevated CO2 strongly stimulated plant growth under high VPD conditions, but this beneficial effect was not observed under low VPD. Under low VPD, elevated CO2 also did not enhance plant photosynthesis, and plant water stress was greatest for plants grown at elevated CO2 and low VPD. Moreover, plants grown under elevated CO2 and low VPD had a lower leaf soluble protein and photosynthetic activity (photosynthetic rate and carboxylation efficiency) than plants grown under elevated CO2 and high VPD. Elevated CO2 significantly increased leaf adaxial and abaxial temperatures. Because the effects of elevated CO2 were dependent on vapour pressure deficit, VPD needs to be controlled in experiments studying the effect of elevated CO2 as well as considered in the extrapolations of results to a warmer, high-CO2 world.  相似文献   

14.
Abstract. The effect of short-term SO2 fumigation on photosynthesis and transpiration of Vicia faba L. was measured at different irradiances and SO2 concentrations. At high irradiances photosynthetic rates were reduced when leaves were exposed to SO2 and the magnitude of the reduction was linearly related to the rate of SO2 uptake through the stomata. Photosynthetic rates stabilized within 2 h after the start of fumigation.
The effect of SO2 on photosynthesis was measured at different CO2 concentrations to analyse the contribution of stomatal and non-stomatal factors to photosynthetic inhibition. Mesophyll resistance to CO2 diffusion increased as a result of SO2 exposure and caused a rapid reduction in photosynthesis after the start of fumigation. Stomatal resistance was not affected directly by SO2 fumigation, but indirectly as a result of a feedback loop between net photosynthesis and internal CO2 concentration.
Analysis of gas-exchange measurements in biochemical terms indicated that photosynthetic inhibition during SO2 exposure can be explained by a stronger reduction in the affinity of RBP carboxylase/oxygenase for CO2 than for O2.  相似文献   

15.
Abstract. While a short-term exposure to elevated atmospheric CO2 induces a large increase in photosynthesis in many plants, long-term growth in elevated CO2 often results in a smaller increase due to reduced photosynthetic capacity. In this study, it was shown that, for a wild C3 species growing in its natural environment and exposed to elevated CO2 for four growing seasons, the photosynthetic capacity has actually increased by 31%. An increase in photosynthetic capacity has been observed in other species growing in the field, which suggests that photosynthesis of certain field grown plants will continue to respond to elevated levels of atmospheric CO2  相似文献   

16.
Elevated CO2 appears to be a significant factor in global warming, which will likely lead to drought conditions in many areas. Few studies have considered the interactive effects of higher CO2, temperature and drought on plant growth and physiology. We grew canola ( Brassica napus cv. 45H72) plants under lower (22/18°C) and higher (28/24°C) temperature regimes in controlled-environment chambers at ambient (370 μmol mol−1) and elevated (740 μmol mol−1) CO2 levels. One half of the plants were watered to field capacity and the other half at wilting point. In three separate experiments, we determined growth, various physiological parameters and content of abscisic acid (ABA), indole-3-acetic acid and ethylene. Drought-stressed plants grown under higher temperature at ambient CO2 had decreased stem height and diameter, leaf number and area, dry matter, leaf area ratio, shoot/root weight ratio, net CO2 assimilation and chlorophyll fluorescence. However, these plants had increased specific leaf weight, leaf weight ratio and chlorophyll concentration. Elevated CO2 generally had the opposite effect, and partially reversed the inhibitory effects of higher temperature and drought on leaf dry weight accumulation. This study showed that higher temperature and drought inhibit many processes but elevated CO2 partially mitigate some adverse effects. As expected, drought stress increased ABA but higher temperature inhibited the ability of plants to produce ABA in response to drought.  相似文献   

17.
基于干旱频率增加、强度增大这一全球降水变化背景, 探究干旱-复水条件下不同功能群(C3和C4)植物的光合生理响应及生长适应策略有助于预测降水格局变化条件下草地的植被组成和生态系统功能。该研究采用盆栽实验, 以松嫩草地生长的一年生C3 (4种)和C4 (3种)牧草为实验材料, 设置了对照、中度干旱和重度干旱3个水分处理水平, 在干旱末期及复水期对植物进行气体交换、生物量和比叶质量的测量。在干旱条件下, 各物种净光合速率和气孔导度均呈下降趋势, 水分利用效率呈上升趋势。干旱对不同植物光合指标的影响存在功能群差异, 随干旱程度的增加C4植物逐渐丧失光合优势, 重度干旱对C4植物净光合速率的影响较C3植物更加明显。由于干旱条件下C3植物光合固碳主要受气孔限制而C4植物主要受代谢限制, 因此复水后C4植物净光合速率恢复速度较C3植物慢。干旱条件下, 各物种的生物量降低, 根冠比和比叶质量升高, 干旱对C3植物各生长指标的影响均大于C4植物; 复水处理后, C3植物生物量随干旱强度增加呈下降趋势, 而C4植物的生物量与对照相比无显著差异。  相似文献   

18.
Effects of source-sink relations on photosynthetic acclimation to elevated CO2   总被引:17,自引:11,他引:6  
Abstract. While photosynthesis of C3 plants is stimulated by an increase in the atmospheric CO2 concentration, photosynthetic capacity is often reduced after long-term exposure to elevated CO2. This reduction appears to be brought about by end product inhibition, resulting from an imbalance in the supply and demand of carbohydrates. A review of the literature revealed that the reduction of photosynthetic capacity in elevated CO2 was most pronounced when the increased supply of carbohydrates was combined with small sink size. The volume of pots in which plants were grown affected the sink size by restricting root growth. While plants grown in small pots had a reduced photosynthetic capacity, plants grown in the field showed no reduction or an increase in this capacity. Pot volume also determined the effect of elevated CO2 on the root/shoot ratio: the root/shoot ratio increased when root growth was not restricted and decreased in plants grown in small pots. The data presented in this paper suggest that plants growing in the field will maintain a high photosynthetic capacity as the atmospheric CO2 level continues to rise.  相似文献   

19.
Abstract. Plantago maritima L. was grown at three levels of salinity, 50, 200, 350 mol m−3 NaCl, and the effects on growth, ion content and photosynthetic capacity were studied. Shoot and root dry weight, leaf production and leaf length were all substantially reduced in plants grown at high salinity. Total leaf area of plants grown at 350 mol m−3 NaCl was only 20% of that in plants at low salinity. Both the Na+ and K+ content of leaves and roots increased with external salinity. There was no change in the Na+/K+ ratio of leaves or roots at different salinity levels. Despite the large reductions in growth and high accumulation of Na+ ions, leaf photosynthetic rate was only slightly reduced by salinity stress. The reduction in photosynthesis was not caused by reduced biochemical capacity as judged by photosynthetic response to intercellular CO2 and by ribulose-1,5-bisphosphate carboxylase activity, but was due to reduced leaf conductance and low intercellular CO2 concentration. The increased stomatal limitation of photosynthesis resulted in higher water-use efficiency of plants grown at high salinity.  相似文献   

20.
Within its wide range across Canada, jack pine is exposed to salinity from both natural and anthropogenic sources. To compare the effects of Cl and SO4 on salt injury, sand and solution-culture grown jack pine ( Pinus banksiana Lamb.) seedlings were treated with nutrient solutions containing 60 or 120 m M NaCl, 60 m M Na2SO4, or a mixture of 60 m M NaCl and 30 m M Na2SO4. After 5 weeks of salt treatments, concentrations of Cl, K, Na, and SO4 were determined in roots, stem and needles of the current and previous years growth, and in necrotic needles. To determine the role of water uptake in the absorption and translocation of salts in plants, total transpiration was measured as the loss of water from a sealed system and related to total plant uptake of Cl, Na, and SO4. Sodium uptake and root-to-shoot transport rates were greater in treatments containing Cl. A delay in root-to-shoot transport of both Na and Cl indicates retention of these ions in the roots. Electrolyte leakage of needles was more closely related to treatment Cl concentrations than treatment Na concentrations. The transport of Na ions to the shoot was related to the presence of Cl, but was not related to transpiration rate.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号