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1.
The effect of SO 2 on the photosynthesis of Clethra barbinervis collected from a smoke-polluted area near the Ashio copper smelter in Tochigi Prefecture was compared with C. barbinervis collected from a nonpolluted district in Tsukuba, Ibaraki Prefecture and Quercus mongolica var. grosseserrata grown in a nonpolluted field in Nagano Prefecture. The plants were exposed to 0.5–1.5 p.p.m. SO 2 for 90 min (short-term) and to 0.3 p.p.m. SO 2 for 31–39 days (long-term). The Clethra plants from both sites had a lower intrinsic stomatal conductance and photosynthetic rate than Quercus plants. Short-and long-term fumigation caused stomatal closure in Quercus plants, but had little effect on the stomatal conductance of Clethra plants. Under short-term fumigation, nonstomatal photosynthetic inhibition per unit of absorbed SO 2 was smallest in Clethra plants from Ashio. Long-term fumigation caused photosynthetic decline and visible foliar injury to Quercus plants, but had no effect on Clethra plants from Ashio. Consequently, Clethra plants from Ashio had a higher photosynthetic rate than Quercus plants after long-term fumigation. These results suggest that C. barbinervis populations in the smoke-polluted area of Ashio had evolved high SO 2 resistance connected with SO 2 detoxification ability in mesophyll cells. 相似文献
2.
Fumigation of leaves with SO 2 can reduce the capacity for photosynthetic CO 2 uptake even in the absence of visible symptoms of damage. In vitro studies suggest that this invisible injury to intact leaves could be affected by damage to each of the main stages in the photosynthetic process. Reduced stomatal apertures may also reduce photosynthesis following SO 2 fumigation. The responses of CO 2 uptake by leaves to intercellular CO 2 concentration and to absorbed light provide information for quantitative separation of the in vivo contribution of the different stages of photosynthesis to reduction in overall rate. This study uses these techniques to examine the basis of reduction in CO 2 uptake in Zea mays cv. LG11 leaves following short-term fumigation with SO 2. Fumigation with 33 μmol m –3 SO 2 for 30 min reduced light saturated CO 2 uptake by about one-third. An even greater reduction in light limited CO 2 uptake was observed and with no significant change in light absorptance this was attributed to a reduced quantum yield of photosynthesis. The light saturated CO 2 uptake rate and the stomatal conductance decreased in parallel. However, the relationship of CO 2 uptake to the intercellular CO 2 concentration suggested that the reduced stomatal conductance did not account for the reduced rate of CO 2 uptake following fumigation. Both the initial slope and plateau of this relationship were significantly reduced, suggesting that both carboxylation efficiency and capacity for regeneration of CO 2 acceptor were diminished by SO 2 fumigation. The operating intercellular CO 2 concentration indicated that both processes were co-limiting, before and after fumigation. The time required for induction of photosynthetic CO 2 uptake on illumination was approximately doubled following SO 2 fumigation, showing that fumigation impairs the ability of the photosynthetic apparatus to adapt to fluctuations in light level. 相似文献
3.
Summary A unique gas exchange system is described in which photosynthesis, transpiration, and stomatal conductance can be measured on leaves during SO 2 fumigations. SO 2 concentrations can be continuously monitored and manipulated between 0 and 2.0 ppm. Rates of total SO 2 uptake and SO 2 absorption through stomates of a fumigated leaf can also be determined.Using this system we compared the effects of SO 2 on the gas exchange rates of two shrub species that co-occur in the Califormian chaparral. Diplacus aurantiacus, a deciduous shrub, was more sensitive to SO 2 fumigation than Heteromeles arbutifolia, an evergreen shrub. The differences in photosynthetic sensitivity could be attributed, in large part, to differential SO 2 absorption rates. 相似文献
4.
The effects of SO 2 on stomatal aperture of attached sunflower leaves were observed with a remote-control light microscope system that permitted continuous observation of stomatal responses over periods of several hours. The relationship between actual stomatal aperture and stomatal conductance, measured with a porometer, also was examined on leaves before and after exposure to SO 2. A distinction between uninjured and injured regions was clearly visible on leaves after exposure to 1.5 microliters per liter SO2 for less than an hour. During the exposure, the mean value of apertures for many stomata, which indicates stomatal conductance and transpiration rate, tended to decrease simultaneously in the uninjured and injured regions. However, the rate of decrease in the injured region was slower than that in the uninjured region because of a transient opening induced by water-soaking in the injured region. The transient opening was less common in stomata near veins and veinlets. There was a good correlation between pore width and stomatal conductance measured with a porometer before exposure to SO2. This correlation continued in leaves exposed to SO2 until visible, irreversible injury occurred, but then it disappeared. The results of these experiments indicate the necessity of continuous observation of individual stomata under the microscope to understand the effects of air pollutants such as SO2 on stomatal behavior. 相似文献
5.
Summary In an effort to predict SO 2 sensitivity of plants from their morphological and physiological features, the effects of SO 2 on photosynthesis were partitioned between stomatal and nonstomatal components for a drought deciduous shrub, Diplacus aurantiacus, and an evergreen shrub, Heteromeles arbutifolia. As predicted, the drought deciduous shrub had the higher gas conductance, and hence SO 2 absorptance. However, nonstomatal components also play a role in determining SO 2 sensitivity. Apparently a plant with a high intrinsic photosynthetic capacity will be more sensitive to SO 2 than one with a lower capacity. 相似文献
6.
Abstract. The effect of gradually-developing water-stress has been studied in Lupinus albus L., Helianthus annuus L., Vitis vinifera cv. Rosaki and Eucalyptus globulus Labill. Water was withheld and diurnal rhythms were investigated 4–8d later, when the predawn water deficit was more negative than in watered plants, and the stomata closed almost completely early during the photoperiod. The contribution of ‘stomatal’ and ‘non-stomatal’ components to the decrease of photosynthetic rate was investigated by (1) comparing the changes of the rate of photosynthesis in air with the changes of stomatal conductance and (2) measuring photosynthetic capacity in saturating irradiance and 15% CO 2. Three species (lupin, eucalyptus and sunflower) showed larger changes of stomatal conductance than photosynthesis in air, and showed little or no decrease of photosynthetic capacity in saturating CO 2. Photosynthesis in air also recovered fully overnight after watering the plants in the evening. In grapevines, stomatal conductance and photosynthesis in air changed in parallel, there was a marked decrease of photosynthetic capacity, and photosynthesis and stomatal conductance did not recover overnight after watering water-stressed plants. Relative water content remained above 90% in grapevine. We conclude that non-stomatal components do not play a significant role in lupins, sunflower or eucalyptus, but could in grapevine. The effect of water-stress on partitioning of photosynthate was investigated by measuring the amounts of sucrose and starch in leaves during a diurnal rhythm, and by measuring the partitioning of 14C-carbon dioxide between sucrose and starch. In all four species, starch was depleted in water-stressed leaves but sucrose was maintained at amounts similar to, or higher than, those in watered plants. Partitioning into sucrose was increased in lupins and eucalyptus, and remained unchanged in grapevine and sunflower. It is concluded that water-stressed leaves in all four species maintain high levels of soluble sugars in their leaves, despite having lower rates of field photosynthesis, decreased rates of export, and low amounts of starch in their leaves. 相似文献
7.
Rates of net photosynthesis, PN, and dark respiration of Viciafaba plants were measured in the laboratory in clean air andin air containing up to 175 parts 10 9 (500 µg m 3)SO 2. At all SO 2 concentrations exceeding 35 parts 10 9,P N was inhibited compared with clean air. At light saturation,the magnitude of inhibition depended on SO 2 concentration butat low irradiances the inhibition was independent of concentration.Dark respiration rates increased substantially, independentof concentration. When exposures continued for up to 3 days, PN returned to clean air values about 1 h after fumigation ceased:dark respiration recovered after one photoperiod. There wereno visible injuries. Reviewing possible mechanisms responsible for the inhibitionof PN, it is suggested that SO 2 competes with CO 2 for bindingsites in RuBP carboxylase. Analysis of resistance analoguesdemonstrates that SO 2 altered both stomatal and internal (residual)resistances. A model of crop photosynthesis shows the implications of theobserved responses for the growth of field crops in which plantsare assumed to respond like laboratory plants. Photosynthesisof the crop would be less sensitive than that of individualplants to SO 2 concentration. Daily dry matter accumulation ofhypothetical polluted crops would be substantiallyless than clean air values but would vary relatively littlewith SO 2 concentration. It is concluded that physiological basesexist to account for observed reductions in growth of plantsat very low SO 2 concentrations, and that thresholds for plantresponses to SO 2 require reassessment. 相似文献
8.
Persistent circadian rhythms in photosynthesis and stomatal opening occurred in bean ( Phaseolus vulgaris L.) plants transferred from a natural photoperiod to a variety of constant conditions. Photosynthesis, measured as carbon
assimilation, and stomatal opening, as conductance to water vapor, oscillated with a freerunning period close to 24 h under
constant moderate light, as well as under light-limiting and CO 2-limiting conditions. The rhythms damped under constant conditions conducive to high photosynthetic rates, as did rates of
carbon assimilation and stomatal conductance, and this damping correlated with the accumulation of carbohydrate. No rhythm
in respiration occurred in plants transferred to constant darkness, and the rhythm in stomatal opening damped rapidly in constant
darkness. Damping of rhythms also occurred in leaflets exposed to constant light and CO 2-free air, demonstrating that active photosynthesis and not simply light was necessary for sustained expression of these rhythms.
This is CIWDPB Publication No. 1142
This research was supported by National Science Foundation grant BSR 8717422 (C.B.F.) and a U.S. Department of Agriculture
training grant to Stanford University (T.L.H.). 相似文献
9.
Summary Experiments were performed on an evergreen ( Heteromeles arbutifolia) and a drought deciduous shrub ( Diplacus aurantiacus) to determine, 1) whether approaches for evaluating SO 2 absorption by leaves in laboratory studies could be extended to field studies, 2) the effects of irrigation on metabolism and SO 2 responses of the study species during a season when water was limiting, 3) to interpret SO 2 responses on the basis of SO 2 flux rates. Laboratory-developed approaches for evaluating SO 2 absorption by leaves were found to be suitable for use with field plants, despite field plants having lower gas exchange rates. Supplementing water during times of deficit did not override all the biological and environmental factors that limited photosynthesis ( A). Irrigation increased leaf longevity of D. aurantiacus, and stomatal conductance to water vapour ( g); g was also shown to increase with H. arbutifolia on irrigation. Irrigation profoundly influenced plant response to SO 2. Unwatered D. aurantiacus had only a small g and therefore a reduced capacity to absorb SO 2 and respond to SO 2; which resulted in apparent SO 2 avoidance. Water availability and SO 2 both affect g and therefore, SO 2 flux rates into the mesophyll. Different ambient SO 2 concentrations of 8.3 and 26.2 mol m -3 (0.2 and 0.6 ppm) were both found to result in similar SO 2 flux rates into the leaf, due to variations in g in response to water availability. Changes in g did not always result in changes in A, implying that carbon fixation may be little affected by some SO 2 exposures, although still potentially affecting such processes as maintenance of leaf water potential, transpirational cooling and nutrient uptake.Abbreviations SO 2
sulphur dioxide
-
A
net photosynthesis
-
E
transpiration
-
g
stomatal conductance to water vapour
- W
Water vapour mole fraction difference between the leaf and air
-
WUE
water use efficiency (mol CO 2 uptake per mol H 2O transpired) 相似文献
10.
CO 2 and water vapor exchange studies of intact plants of black needle rush ( Juncus roemerianus Scheele) were conducted in an undisturbed marsh community on Sapelo Island, Georgia. The seasonal patterns of the light and temperature responses of net photosynthesis, transpiration, leaf diffusive conductance, water-use efficiency and respiration were determined five times over the year. Internal resistances to CO 2 uptake were also evaluated. Net photosynthesis was highest in early spring, but declined only slightly through the year. A distinct and moderate temperature optimum of net photosynthesis was observed with decreasing rates above 30 C. Leaf conductances to water vapor were similar at all seasons and were high at cooler temperatures and decreased with increasing temperature. Transpiration was relatively high and constant during all seasons. The water-use efficiency of photosynthesis was high below 25 C, but decreased sharply above that temperature. Dark respiration was relatively low. Seasonal changes reflected changes in leaf density. Decreasing stomatal conductances and increasing respiration rates reduced net photosynthesis at higher temperatures. The stomatal resistance increased and internal resistances to CO 2 uptake decreased over the year, but the total resistance remained constant. The internal resistance to CO 2 uptake was consistently higher than the stomatal resistance. These seasonal response patterns show that J. roemerianus is well adapted to the seasonal changes in ambient temperature and irradiance and other microenvironmental factors in the high marsh. These physiological characteristics permit this C 3 species to maintain a high productivity in a seasonally hot and stressful environment. 相似文献
11.
Stomata mediate gas exchange between the inter‐cellular spaces of leaves and the atmosphere. CO 2 levels in leaves ( Ci) are determined by respiration, photosynthesis, stomatal conductance and atmospheric [CO 2]. [CO 2] in leaves mediates stomatal movements. The role of guard cell photosynthesis in stomatal conductance responses is a matter of debate, and genetic approaches are needed. We have generated transgenic Arabidopsis plants that are chlorophyll‐deficient in guard cells only, expressing a constitutively active chlorophyllase in a guard cell specific enhancer trap line. Our data show that more than 90% of guard cells were chlorophyll‐deficient. Interestingly, approximately 45% of stomata had an unusual, previously not‐described, morphology of thin‐shaped chlorophyll‐less stomata. Nevertheless, stomatal size, stomatal index, plant morphology, and whole‐leaf photosynthetic parameters (PSII, qP, qN, FV′/ FM′) were comparable with wild‐type plants. Time‐resolved intact leaf gas‐exchange analyses showed a reduction in stomatal conductance and CO 2‐assimilation rates of the transgenic plants. Normalization of CO 2 responses showed that stomata of transgenic plants respond to [CO 2] shifts. Detailed stomatal aperture measurements of normal kidney‐shaped stomata, which lack chlorophyll, showed stomatal closing responses to [CO 2] elevation and abscisic acid (ABA), while thin‐shaped stomata were continuously closed. Our present findings show that stomatal movement responses to [CO 2] and ABA are functional in guard cells that lack chlorophyll. These data suggest that guard cell CO 2 and ABA signal transduction are not directly modulated by guard cell photosynthesis/electron transport. Moreover, the finding that chlorophyll‐less stomata cause a ‘deflated’ thin‐shaped phenotype, suggests that photosynthesis in guard cells is critical for energization and guard cell turgor production. 相似文献
12.
Plants of five clones of Populus tremuloides Michx. were exposed to 0, 0.2 or 0.5 microliter per liter SO 2 for 8 hours in controlled environment chambers. In the absence of the pollutant, two pollution-resistant clones maintained consistently lower daytime diffusive conductance (LDC) than did a highly susceptible clone or two moderately resistant clones. Differences in LDC among the latter three clones were not significant. At 0.2 microliter per liter SO 2, LDC decreased in the susceptible clone after 8 hours fumigation while the LDC of the other clones was not affected. Fumigation with 0.5 microliter per liter SO 2 decreased LDC of all five clones during the fumigation. Rates of recovery following fumigation varied with the clone, but the LDC of all clones had returned to control values by the beginning of the night following fumigation. Night LDC was higher in the susceptible clone than in the other clones. Fumigation for 16 hours (14 hours day + 2 hours night) with 0.4 microliter per liter SO 2 decreased night LDC by half. Sulfur uptake studies generally confirmed the results of the conductance measurements. The results show that stomatal conductance is important in determining relative susceptibility of the clones to pollution stress. 相似文献
13.
The effect of iron solid particulate matter (SPM Fe) deposited onto soil and leaves on photosynthesis and oxidative stress was evaluated in Clusia hilariana, a CAM tropical tree of high occurrence in Brazilian restingas. Significant increases in iron content were found in plants
exposed to SPM Fe applied onto leaf and soil surfaces. However, only the application of SPM Fe on leaves of C. hilariana caused significant reductions in some evaluated characteristics such as photosynthetic rate, stomatal conductance, transpiration,
organic acid accumulation, potential quantum yield of PSII, and changes in daily CAM photosynthesis pattern. Increase in relative
membrane permeability and reduction in catalase and superoxide dismutase activities in the leaves of plants exposed to SPM Fe also were observed; however, lipid peroxidation did not change. These responses seem to be due to the combination of physical
effects such as increase of leaf temperature, reduction in light absorption, obstruction of stomatal pores, and biochemical
effects triggered by oxidative stress. 相似文献
14.
Fifty-day-old Cichorium intybus Linn, plants were exposed to 1 ppm sulfur dioxide gas, 2 h per day for 7 consecutive days. Their leaves as well as those
from the control plants were sampled at pre-flowering, flowering, and post-flowering stages to study their morphological,
physiological, and biochemical responses to SO 2 stress. The number, dimensions, area, and biomass of leaves were less in the treated plants. Length and width of stomatal
apertures on both epidermises were greater for leaves exposed to SO 2. The Stomata were longer on the adaxial epidermis, but shorter on the abaxial epidermis, except at the pre-flowering stage.
Stomatal widths varied widely. Compared with the controls, the abaxial epidermis on treated leaves showed consistently lower
stomatal densities as well as stomatal indices. This was also true for the adaxial epidermis during the post-flowering stage.
The photosynthetic rate and stomatal conductance were reduced in the SO 2-exposed plants, but intercellular CO 2 concentrations increased at the pre-flowering stage and, subsequently, declined. Chlorophyll a, carotenoid, and total chlorophyll
contents increased at the pre-flowering stage, and then decreased. The level of chlorophyll b was reduced throughout plant development compared with the untreated controls. 相似文献
15.
The joint action of O 3 and SO 2 stress on plants was investigated by determining the quantitative relationship between air pollutant fluxes and effects on stomatal conductance. Gas exchange measurements of O 3, SO 2, and H 2O vapor were made for Pisum sativum L. (garden pea). Plants were grown under controlled environments, and O 3, SO 2, and H 2O vapor fluxes were evaluated with a whole-plant gas exchange chamber using the mass-balance approach. Maximum O 3 and SO 2 fluxes per unit area (2 sided) into leaves averaged 8 nanomoles per square meter per second with exposure to either O 3 or SO 2 at 0.1 microliters per liter. Internal fluxes of either O 3 or SO 2 were reduced by up to 50% during exposure to combined versus individual pollutants; the greatest reduction occurred with simultaneous versus sequential combinations of the pollutants. Stomatal conductance to H 2O was substantially altered by the pollutant exposures, with O 3 molecules twice as effective as SO 2 molecules in inducing stomatal closure. Stomatal conductance was related to the integrated dose of pollutants. The regression equations relating integrated dose to stomatal conductance were similar with O 3 alone, O 3 plus added SO 2, and O 3 plus SO 2 simultaneously; i.e. a dose of 100 micromoles per square meter produced a 39 to 45% reduction in conductance over nonexposed plants. With SO 2 alone, or SO 2 plus added O 3, a dose of 100 micromoles per square meter produced a 20 to 25% reduction in conductance. When O 3 was present at the start of the exposure, then stomatal response resembled that for O 3 more than the response for SO 2. This study indicated that stomatal responses with combinations of O 3 and SO 2 are not dependent solely on the integrated dose of pollutants, but suggests that a metabolic synergistic effect exists. 相似文献
16.
The responsiveness to ethylene of net photosynthesis and stomatal conductance to water vapor in intact plants was investigated in 13 herbaceous species representing seven plant families. Exposures were conducted in an open, whole-plant exposure system providing controlled levels of irradiance, air temperature, CO 2, relative humidity, and ethylene concentration. Net photosynthesis and stomatal conductance to water vapor in units of moles per square meter per second were measured on recently expanded leaves in control and ethylene-treated plants using a remotely operated single-leaf cuvette. The ethylene concentration was either 0 or 210 micromoles per cubic meter and was maintained for 4 hours. Species varied substantially in the response of their foliar gas exchange to ethylene. In 7 of the 13 species, net photosynthesis was inhibited statistically by 4 hours of ethylene exposure. As a function of the rate in control plants, the responses were most pronounced and statistically significant in Arachis hypogaea (−51.1%), Gossypium hirsutum (−31.7%), Glycine max (−24.8%), Cucurbita pepo (−20.4%), Phaseolus vulgaris (−18.4%), Setaria viridis (−17.5%), and Raphanus sativus (−4.4%). Whereas the responsiveness of net photosynthesis to ethylene among the 13 species showed no specific taxonomic associations, the responsiveness was positively correlated with the intrinsic rate of net photosynthesis. Stomatal conductance to water vapor after 4 hours of ethylene exposure declined statistically in 6 of the 13 species. As a function of control rates, the most marked and statistically significant responses of stomatal conductance were in Glycine max (−53.6%), Gossypium hirsutum (−51.2%), Arachis hypogaea (−42.7%), Phaseolus vulgaris (−38.6%), Raphanus sativus (−26.8%), and Solanum tuberosum (−23.4%). Although ethylene-induced changes in net photosynthesis and stomatal conductance were positively correlated, there were species-specific exceptions in which net photosynthesis declined after 4 hours of exposure without a concurrent change in stomatal conductance, stomatal conductance declined without a change in net photosynthesis, and the decline in stomatal conductance substantially exceeded the corresponding decline in net photosynthesis. Thus, the responsiveness to ethylene of net photosynthesis and stomatal conductance to water vapor were not consistently synchronous or equivalent among the 13 species. It is concluded that foliar gas exchange is responsive to exogenously applied ethylene in many plant species. The sensitivity of foliar gas exchange to ethylene may play a role in general plant response to environmental stress in which one of the physiological sites of action for endogenously produced stress ethylene in the leaf is the plant's photosynthetic capacity and/or stomatal conductance to water vapor. 相似文献
17.
A close correlation between stomatal conductance and the steady-state photosynthetic rate has been observed for diverse plant species under various environmental conditions. However, it remains unclear whether stomatal conductance is a major limiting factor for the photosynthetic rate under naturally fluctuating light conditions. We analysed a SLAC1 knockout rice line to examine the role of stomatal conductance in photosynthetic responses to fluctuating light. SLAC1 encodes a stomatal anion channel that regulates stomatal closure. Long exposures to weak light before treatments with strong light increased the photosynthetic induction time required for plants to reach a steady-state photosynthetic rate and also induced stomatal limitation of photosynthesis by restricting the diffusion of CO 2 into leaves. The slac1 mutant exhibited a significantly higher rate of stomatal opening after an increase in irradiance than wild-type plants, leading to a higher rate of photosynthetic induction. Under natural conditions, in which irradiance levels are highly variable, the stomata of the slac1 mutant remained open to ensure efficient photosynthetic reaction. These observations reveal that stomatal conductance is important for regulating photosynthesis in rice plants in the natural environment with fluctuating light. 相似文献
18.
We analysed the impact of elevated CO 2 on water relations, water use efficiency and photosynthetic gas exchange in barley ( Hordeum vulgare L.) under wet and drying soil conditions. Soil moisture was less depleted under elevated compared to ambient [CO 2]. Elevated CO 2 had no significant effect on the water relations of irrigated plants, except on whole plant hydraulic conductance, which was markedly decreased at elevated compared to ambient CO 2 concentrations. The values of relative water content, water potential and osmotic potential were higher under elevated CO 2 during the entire drought period. The better water status of water-limited plants grown at elevated CO 2 was the result of stomatal control rather than of osmotic adjustment. Despite the low stomatal conductance produced by elevated CO 2, net photosynthesis was higher under elevated than ambient CO 2 concentrations. With water shortage, photosynthesis was maintained for longer at higher rates under elevated CO 2. The reduction of stomatal conductance and therefore transpiration, and the enhancement of carbon assimilation by elevated CO 2, increased instantaneous and whole plant water use efficiency in both irrigated and droughted plants. Thus, the metabolism of barley plants grown under elevated CO 2 and moderate or mild water deficit conditions is benefited by increased photosynthesis and lower transpiration. The reduction in plant water use results in a marked increase in soil water content which delays the onset and severity of water deficit. 相似文献
19.
This study tests the hypothesis that potted sweet orange plants show a significant variation in photosynthesis over seasonal and diurnal cycles, even in well-hydrated conditions. This hypothesis was tested by measuring diurnal variations in leaf gas exchange, chlorophyll fluorescence, leaf water potential, and the responses of CO 2 assimilation to increasing air CO 2 concentrations in 1-year-old ‘Valência’ sweet orange scions grafted onto ‘Cleopatra’ mandarin rootstocks during the winter and summer seasons in a subtropical climate. In addition, diurnal leaf gas exchange was evaluated under controlled conditions, with constant environmental conditions during both winter and summer. In relation to our hypothesis, a greater rate of photosynthesis is found during the summer compared to the winter. Reduced photosynthesis during winter was induced by cool night conditions, as the diurnal fluctuation of environmental conditions was not limiting. Low air and soil temperatures caused decreases in the stomatal conductance and in the rates of the biochemical reactions underlying photosynthesis (ribulose-1,5-bisphosphate (RuBP) carboxylation and RuBP regeneration) during the winter compared to the values obtained for those markers in the summer. Citrus photosynthesis during the summer was not impaired by biochemical or photochemical reactions, as CO 2 assimilation was only limited by stomatal conductance due to high leaf-to-air vapor pressure difference ( VPD) during the afternoon. During the winter, the reduction in photosynthesis during the afternoon was caused by decreases in RuBP regeneration and stomatal conductance, which are both precipitated by low night temperature. 相似文献
20.
The response of adaxial and abaxial stomatal conductance in Rumex obtusifolius to growth at elevated atmospheric concentrations of CO 2 (250 μmol mol ?1 above ambient) was investigated over two growing seasons. The conductance of both the adaxial and abaxial leaf surfaces was found to be reduced by elevated concentrations of CO 2. Elevated CO 2 caused a much greater reduction in conductance for the adaxial surface than for the abaxial surface. The absence of effects upon stomatal density indicated that the reductions were probably the result of changes in stomatal aperture. Partitioning of gas exchange between the leaf surfaces revealed that increased concentrations of CO 2 caused increased rates of photosynthesis only via the abaxial surface. Additionally, leaf thickness was found to increase during growth at elevated concentrations of CO 2. The tendency for these amphistomatous leaves to develop a distribution of conductance approaching that of hypostomatous leaves clearly reduced their maximum photosynthetic potential. This conclusion was supported by measurements of stomatal limitation, which showed greater values for the adaxial surfaces, and greater values at elevated CO 2. This reduction in photosynthesis may in part be caused by higher diffusive limitations imposed because of increased leaf thickness. In an uncoupled canopy, asymmetrical stomatal responses of the kind identified here may appreciably reduce transpiration. Species which show symmetrical responses are less likely to show reduced transpirational rates, and a redistribution of water loss between species may occur. The implications of asymmetrical stomatal responses for photosynthesis and canopy transpiration are discussed. 相似文献
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