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1.
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The effects of ozone exposure on lettuce leaves were investigated by means of gas exchange, modulated chlorophyll a fluorescence and antioxidants systems. High ozone concentration decreased the rate of photosynthesis at light saturation level and changes in stomatal conductance and transpiration rate. However, an increase in intercellular CO2 concentration indicated a decrease in the carboxylation efficiency. These data agreed with a reduction of non-cyclic electron flow and lower capacity to reduce the quinone pool. Ozone affected the ascorbate pool and decreased ascorbate peroxidase activity, increased lipid peroxidation, altered membrane properties and reduced the development of non-photochemical quenching.  相似文献   

3.
Abstract. A portable apparatus has been constructed to measure simultaneously the quantum yield of CO2 assimilation, light absorption, chlorophyll fluorescence emission and water vapour exchange of attached intact leaves in the field. The core of the instrument is a light-integrating spherical leaf chamber which includes ports for a light source, photosynthetically active radiation sensor, fluorescence probes and gas inlet and outlet manifolds. Measurement of the quantum flux inside the empty chamber and with a leaf present allows determination of leaf absorptance. An open gas exchange system is employed using an infra-red analyser to measure leaf CO2 exchange. Using a DC white light source the quantum yield of CO2 assimilation based on absorbed light (φabs) may be determined rapidly in either ambient air or artificial gas mixtures. Inclusion of capacitance humidity probes into the gas inlet and outlet ports allows simultaneous determination of water vapour exchange and subsequent estimation of stomatal conductance to CO2 and intercellular CO2 concentration. Measurement of fluorescence emission by the sample leaf exposed to white light is achieved by a modulated fluorescence detection system. In addition to determination of the minimal, maximal and variable fluorescence levels, a further analysis allows the photochemical and non-photochemical components of fluorescence quenching, to be estimated. The theory and design of this apparatus is described in detail. The use of the apparatus in the field is demonstrated through a study of the photosynthetic performance of a maize and bean crop during the growing season and by analysis of the photosynthetic performance of crops subjected to nitrogen-stress and a herbicide treatment.  相似文献   

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We report the results of a 2‐year study of effects of the elevated (current ambient plus 350 μmol CO2 mol?1) atmospheric CO2 concentration (Ca) on net ecosystem CO2 exchange (NEE) of a scrub–oak ecosystem. The measurements were made in open‐top chambers (OTCs) modified to function as open gas‐exchange systems. The OTCs enclosed samples of the ecosystem (ca. 10 m2 surface area) that had regenerated after a fire, 5 years before, in either current ambient or elevated Ca. Throughout the study, elevated Ca increased maximum NEE (NEEmax) and the apparent quantum yield of the NEE (φNEE) during the photoperiod. The magnitude of the stimulation of NEEmax, expressed per unit ground area, was seasonal, rising from 50% in the winter to 180% in the summer. The key to this stimulation was effects of elevated Ca, and their interaction with the seasonal changes in the environment, on ecosystem leaf area index, photosynthesis and respiration. The separation of these factors was difficult. When expressed per unit leaf area the stimulation of the NEEmax ranged from 7% to 60%, with the increase being dependent on increasing soil water content (Wsoil). At night, the CO2 effluxes from the ecosystem (NEEnight) were on an average 39% higher in elevated Ca. However, the increase varied between 6% and 64%, and had no clear seasonality. The partitioning of NEEnight into its belowground (Rbelow) and aboveground (Rabove) components was carried out in the winter only. A 35% and 27% stimulation of NEEnight in December 1999 and 2000, respectively, was largely due to a 26% and 28% stimulation of Rbelow in the respective periods, because Rbelow constituted ca. 87% of NEEnight. The 37% and 42% stimulation of Rabove in December 1999 and 2000, respectively, was less than the 65% and 80% stimulation of the aboveground biomass by elevated Ca at these times. An increase in the relative amount of the aboveground biomass in woody tissue, combined with a decrease in the specific rate of stem respiration of the dominant species Quercus myrtifolia in elevated Ca, was responsible for this effect. Throughout this study, elevated Ca had a greater effect on carbon uptake than on carbon loss, in terms of both the absolute flux and relative stimulation. Consequently, for this scrub–oak ecosystem carbon sequestration was greater in the elevated Ca during this 2‐year study period.  相似文献   

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The ability of seedlings to tolerate temperature extremes is important in determining the distribution of perennial plants in the arid south-western USA, and the manner in which elevated CO2 impacts the ability of plants to tolerate high temperatures is relatively unknown. Whereas the effects of chronic high temperature (30–38°C) and elevated CO2 are comparatively well understood, little research has assessed plant performance in elevated CO2 during extreme (> 45 °C) temperature events. We exposed three species of Yucca to 360 and 700 μmol CO2 mol–1 for 8 months, then 9 d of high temperature (up to 53 °C) to evaluate the impacts of elevated CO2 on the potential for photosynthetic function during external high temperature. Seedlings of a coastal C3 species (Yucca whipplei), a desert C3 species (Yucca brevifolia), and a desert CAM species (Yucca schidigera), were used to test for differences among functional groups. In general, Yuccas exposed to elevated CO2 showed decreases in carboxylation efficiency as compared with plants grown at ambient before the initiation of high temperature. The coastal species (Y. whipplei) showed significant reductions (33%) in CO2 saturated maximum assimilation rate (Amax), but the desert species (Y. brevifolia and Y. schidigera) showed no such reductions in Amax. Stomatal conductance was lower in elevated CO2 as compared with ambient throughout the temperature event; however, there were species-specific differences over time. Elevated CO2 enhanced photosynthesis in Y. whipplei at high temperatures for a period of 4 d, but not for Y. brevifolia or Y. schidigera. Elevated CO2 offset photoinhibition (measured as Fv/Fm) in Y. whipplei as compared with ambient CO2, depending on exposure time to high temperature. Stable Fv/Fm in Y. whipplei occurred in parallel with increases in the quantum yield of photosystem II (ΦPSII) at high temperatures in elevated CO2. The value of ΦPSII remained constant or decreased with increasing temperature in all other treatment and species combinations. This suggests that the reductions in Fv/Fm resulted from thermal energy dissipation in the pigment bed for Y. brevifolia and Y. schidigera. The greater efficiency of photosystem II in Y. whipplei helped to maintain photosynthetic function at high temperatures in elevated CO2. These patterns are in contrast to the hypothesis that high temperatures in elevated CO2 would increase the potential for photoinhibition. Our results suggest that elevated CO2 may offset high-temperature stress in coastal Yucca, but not in those species native to drier systems. Therefore, in the case of Y. whipplei, elevated CO2 may allow plants to survive extreme temperature events, potentially relaxing the effects of high temperature on the establishment in novel habitats.  相似文献   

8.
Photosynthesis, respiration and chlorophyll fluorescence parameters were determined in peach ( Prunus persica L. cv. Dixired) leaves naturally infected by Taphrina deformans (Berk.) Tul. and in healthy leaves (controls), in two successive springs. A drastic decrease in net photosynthesis and an evident increase in respiration in curled leaves were noted. The instantaneous PSII fluorescence yield, with no (F0) and with (F0) quenching component, and steady state fluorescence yield (under actinic light, Fs) were essentially unchanged. Maximal fluorescence in dark-adapted (Fm) and illuminated (F'm) leaves and the corresponding variable fluorescence (Fv and Fv) clearly decreased. The indicators of PSII quantum yield (Fv/Fm) in dark-adapted leaves, and the potential PSII excitation capture efficiency (F'v/F'm) and the quantum yield of PSII (qp [F'v/F'm]) in the light were also significantly lower in curled leaves. Decreasing tendencies were also noted for the PSII photochemical yield (photochemical quenching, qp) and in the energy status of the chloroplast (non-photochemical quenching, qN, and Stern-Vollmer value, NPQ) although the differences were not always significant. In curled leaves the main alteration documented is the imbalance between the drastic inhibition of CO2 fixation and the moderate decrease in photochemical reactions (i.e. Fv/Fm and ΔF/F'm), indicating changes in the energy flux.  相似文献   

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The gaseous exchange pathways of Sticla latifrons Rich. and Pseudocyphellaria amphisticta Kremp. were examined using both light and scanning electron microscopes. The size and frequency of the pores in the gas exchange structures (cyphellae and pseudocyphellae) and in the medulla were measured and from these CO2 diffusion resistances were calculated. Pseudocyphellae were found to be smaller and more widely spaced than cyphellae, consequently the resistance of the pseudocyphellae, was much greater than that of the cyphellae. Medulla resistances were low in both lichens and are probably unimportant, even at high water contents. No evidence of hyphal swelling was found. Gas exchange structure resistances were more than five fold greater than medulla resistances. It is suggested that this arrangement of resistances may simultaneously encourage refixation of respired CO2 and maintain a non desiccating environment for the lichen algae. The internal transport resistances calculated in this work approximate experimentally obtained values.  相似文献   

12.
Existing methods to estimate the mesophyll conductance to CO2 diffusion ( g m) are often based on combined gas exchange and chlorophyll fluorescence measurements. However, estimations of average g m by these methods are often unreliable either because the range of usable data is too narrow or because the estimations are very sensitive to measurement errors. We describe three method variants to estimate g m, for which a wider range of data are usable. They use curve-fitting techniques, which minimise the sum of squared model deviations from the data for A (CO2 assimilation rate) or for J (linear electron transport rate). Like the existing approaches, they are all based on common physiological principles assuming that electron transport limits A . The proposed variants were far less sensitive than the existing approaches to 'measurement noise' either created randomly in the generated data set or inevitably existing in real data sets. Yet, the estimates of g m from the three variants differed by approximately 15%. Moreover, for each variant, a stoichiometric uncertainty in linear electron transport-limited photosynthesis can cause another 15% difference. Any estimation of g m using gas exchange and chlorophyll fluorescence measurements should be considered with caution, especially when g m is high.  相似文献   

13.
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   

14.
Abstract Associations between photosynthetic responses to CO2 at rate-saturating light and photosynthetic enzyme activities were compared for leaves of maize grown under constant air temperatures of 19, 25 and 31°C. Key photosynthetic enzymes analysed were ribulose bisphosphatc (RuBP) carboxylase, phosphoenolpyruvate (PEP) carboxylase, NADP-malic enzyme and pyruvate, Pi dikinasc. Rates of CO2-saturated photosynthesis were similar in leaves developed at 19°C and 25°C but were decreased significantly by growth at 31°C. In contrast, carboxylation efficiency differed significantly between all three temperature regimes. Carboxylation efficiency was greatest in leaves developed at 19°C and decreased with increasing temperature during growth. The changes of carboxylation efficiency were highly correlated with changes in the activity of pyruvate, Pi dikinase (r= 0.95), but not with other photosynthetic enzyme activities. The activities of these latter enzymes, including that of RuBP carboxylase, were relatively insensitive to temperature during growth. The sensitivity of quantum yield to O2 concentration was lower in leaves grown at 19°C than in leaves grown at 31°C. These observations support the novel hypothesis that variation in the capacity for CO2 delivery to the bundle sheath by the C4 cycle, relative to the capacity for net assimilation by the C2 cycle, can be a principal determinant of C4 photosynthetic responses to CO2.  相似文献   

15.
Atmospheric CO2 (Ca) has risen dramatically since preglacial times and is projected to double in the next century. As part of a 4‐year study, we examined leaf gas exchange and photosynthetic acclimation in C3 and C4 plants using unique chambers that maintained a continuous Ca gradient from 200 to 550 µmol mol?1 in a natural grassland. Our goals were to characterize linear, nonlinear and threshold responses to increasing Ca from past to future Ca levels. Photosynthesis (A), stomatal conductance (gs), leaf water‐use efficiency (A/gs) and leaf N content were measured in three common species: Bothriochloa ischaemum, a C4 perennial grass, Bromus japonicus, a C3 annual grass, and Solanum dimidiatum, a C3 perennial forb. Assimilation responses to internal CO2 concentrations (A/Ci curves) and photosynthetically active radiation (A/PAR curves) were also assessed, and acclimation parameters estimated from these data. Photosynthesis increased linearly with Ca in all species (P < 0.05). S. dimidiatum and B. ischaemum had greater carboxylation rates for Rubisco and PEP carboxylase, respectively, at subambient than superambient Ca (P < 0.05). To our knowledge, this is the first published evidence of A up‐regulation at subambient Ca in the field. No species showed down‐regulation at superambient Ca. Stomatal conductance generally showed curvilinear decreases with Ca in the perennial species (P < 0.05), with steeper declines over subambient Ca than superambient, suggesting that plant water relations have already changed significantly with past Ca increases. Resource‐use efficiency (A/gs and A/leaf N) in all species increased linearly with Ca. As both C3 and C4 plants had significant responses in A, gs, A/gs and A/leaf N to Ca enrichment, future Ca increases in this grassland may not favour C3 species as much as originally thought. Non‐linear responses and acclimation to low Ca should be incorporated into mechanistic models to better predict the effects of past and present rising Ca on grassland ecosystems.  相似文献   

16.
Hylocereus undatus (Haworth) Britton and Rose growing in controlled environment chambers at 370 and 740 μmol CO2 mol?1 air showed a Crassulacean acid metabolism (CAM) pattern of CO2 uptake, with 34% more total daily CO2 uptake under the doubled CO2 concentration and most of the increase occurring in the late afternoon. For both CO2 concentrations, 90% of the maximal daily CO2 uptake occurred at a total daily photosynthetic photon flux density (PPFD) of only 10 mol m?2 day?1 and the best day/night air temperatures were 25/15°C. Enhancement of the daily net CO2 uptake by doubling the CO2 concentration was greater under the highest PPFD (30 mol m?2 day?1) and extreme day/night air temperatures (15/5 and 45/35°C). After 24 days of drought, daily CO2 uptake under 370 μmol CO2 mol?1 was 25% of that under 740 μmol CO2 mol?1. The ratio of variable to maximal chlorophyll fluorescence (Fy/Fm) decreased as the PPFD was raised above 5 mol m?2 day?1, at extreme day/night temperatures and during drought, suggesting that stress occurred under these conditions. Fv/Fm was higher under the doubled CO2 concentration, indicating that the current CO2 concentration was apparently limiting for photosynthesis. Thus net CO2 uptake by the shade-tolerant H. undatus, the photosynthetic efficiency of which was greatest at low PPFDs. showed a positive response to doubling the CO2 concentration, especially under stressful environmental conditions.  相似文献   

17.
1 In a glasshouse experiment we studied the effect of raised CO2 concentration (720 p.p.m.) on CH4 emission at natural boreal peat temperatures using intact cores of boreal peat with living vascular plants and Sphagnum mosses. After the end of the growing season half of the cores were kept unnaturally warm (17–20 °C). The potential for CH4 production and oxidation was measured at the end of the emission experiment.
2 The vascular cores ('Sedge') consisted of a moss layer with sedges, and the moss cores (' Sphagnum ') of Sphagnum mosses (some sedge seedlings were removed by cutting). Methane efflux was 6–12 times higher from the Sedge cores than from the Sphagnum cores. The release of CH 4 from Sedge cores increased with increasing temperature of the peat and decreased with decreasing temperature. Methane efflux from Sphagnum cores was quite stable independent of the peat temperatures.
3 In both Sedge and Sphagnum samples, CO2 treatment doubled the potential CH4 production but had no effect on the potential CH4 oxidation. A raised concentration of CO2 increased CH4 efflux weakly and only at the highest peat temperatures (17–20 °C).
4 The results suggest that in cool regions, such as boreal wetlands, temperature would restrict decomposition of the extra substrates probably derived from enhanced primary production of mire vegetation under raised CO2 concentrations, and would thus retard any consequent increase in CH4 emission.  相似文献   

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A viable wheat hybrid intermediate of the same height as the parents was obtained by crossing the female parent of tall variety NP4 with the male parent of the dwarf variety HD2160. Seeds of the hybrid and its parents were germinated and their growth pattern as well as the activities of peroxidase, indolyl-3-acetic acid oxidase and amylase in extracts made from them were studied at the early seedling stages i.e. up to 96 h.
A positive correlation existed between the length of the axis at the early seedling stage and at mature plant height as far as the parental varieties are concerned but no such correlation was observed with the hybrid. Growth of the hybrid seedlings was less than of its parents. Light appeared to stimulate the longitudinal growth of the axis to different extents in the parents and hybrid. Higher activities of peroxidase, indolyl-3-acetic acid oxidase and amylase were observed in the hybrid as compared to both of its parents. Lethal wheat hybrid also exhibits increased activities of amylase, indolyl-3-acetic acid oxidase and peroxidase. Therefore, it appears that seedling growth and enzyme activities at the seedling stage are not always correlated with hybrid vigour.  相似文献   

20.
Effects of SO2 on Photosynthesis and Nitrogen Fixation   总被引:6,自引:0,他引:6  
Spikelets of Themeda triandra are dormant when mature and require an after-ripening period in dry storage of approximately 12 months before full germination potential is realized. Successful germination of spikelets entails the splitting of the tough upper glumes by radicles. Dormany appears to result from a combination of embryo dormancy and mechanically resistant glumes. Glume removal from dormant spikelets increases germination while glume removal plus gibberellic acid increases germination even more. During the after-ripening period, the growth potential of spikelets and caryopses increases as measured by their ability to germinate in the presence of the osmoticum polyethylene glycol 6000. The inhibition of germination by decreasing osmotic potential of the germination medium significantly interacts with the promotion caused by gibberellic acid indicating that both factors affect germination by altering the growth potential of the embryos. The increase in growth potential during after-ripening is probably related to the synthesis of gibberellin-like substances. It is hypothesized that dormancy breaking during after-ripening occurs because the growth potential of embryos increases and this consequently increases the ability of radicles to split the upper glumes during germination.  相似文献   

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