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1.
CO2 exchange rates per unit dry weight, measured in the field on attached fruits of the late-maturing Cal Red peach cultivar, at 1200 μmol photons m?2S?1 and in dark, and photosynthetic rates, calculated by the difference between the rates of CO2 evolution in light and dark, declined over the growing season. Calculated photosynthetic rates per fruit increased over the season with increasing fruit dry matter, but declined in maturing fruits apparently coinciding with the loss of chlorophyll. Slight net fruit photosynthetic rates ranging from 0. 087 ± 0. 06 to 0. 003 ± 0. 05 nmol CO2 (g dry weight)?1 S?1 were measured in midseason under optimal temperature (15 and 20°C) and light (1200 μmol photons m?2 S?1) conditions. Calculated fruit photosynthetic rates per unit dry weight increased with increasing temperatures and photon flux densities during fruit development. Dark respiration rates per unit dry weight doubled within a temperature interval of 10°C; the mean seasonal O10 value was 2. 03 between 20 and 30°C. The highest photosynthetic rates were measured at 35°C throughout the growing season. Since dark respiration rates increased at high temperatures to a greater extent than CO2 exchange rates in light, fruit photosynthesis was apparently stimulated by high internal CO2 concentrations via CO2 refixation. At 15°C, fruit photosynthetic rates tended to be saturated at about 600 μmol photons m?2 S?1. Young peach fruits responded to increasing ambient CO2 concentrations with decreasing net CO2 exchange rates in light, but more mature fruits did not respond to increases in ambient CO2. Fruit CO2 exchange rates in the dark remained fairly constant, apparently uninfluenced by ambient CO2 concentrations during the entire growing season. Calculated fruit photosynthetic rates clearly revealed the difference in CO2 response of young and mature peach fruits. Photosynthetic rates of younger peach fruits apparently approached saturation at 370 μl CO21?2. In CO2 free air, fruit photosynthesis was dependent on CO2 refixation since CO2 uptake by the fruits from the external atmosphere was not possible. The difference in photosynthetic rates between fruits in CO2-free air and 370 μl CO2 1?1 indicated that young peach fruits were apparently able to take up CO2 from the external atmosphere. CO2 uptake by peach fruits contributed between 28 and 16% to the fruit photosynthetic rate early in the season, whereas photosynthesis in maturing fruits was supplied entirely by CO2 refixation. 相似文献
2.
We present evidence that plant growth at elevated atmospheric CO2 increases the high‐temperature tolerance of photosynthesis in a wide variety of plant species under both greenhouse and field conditions. We grew plants at ambient CO2 (~ 360 μ mol mol ? 1) and elevated CO2 (550–1000 μ mol mol ? 1) in three separate growth facilities, including the Nevada Desert Free‐Air Carbon Dioxide Enrichment (FACE) facility. Excised leaves from both the ambient and elevated CO2 treatments were exposed to temperatures ranging from 28 to 48 °C. In more than half the species examined (4 of 7, 3 of 5, and 3 of 5 species in the three facilities), leaves from elevated CO2‐grown plants maintained PSII efficiency (Fv/Fm) to significantly higher temperatures than ambient‐grown leaves. This enhanced PSII thermotolerance was found in both woody and herbaceous species and in both monocots and dicots. Detailed experiments conducted with Cucumis sativus showed that the greater Fv/Fm in elevated versus ambient CO2‐grown leaves following heat stress was due to both a higher Fm and a lower Fo, and that Fv/Fm differences between elevated and ambient CO2‐grown leaves persisted for at least 20 h following heat shock. Cucumis sativus leaves from elevated CO2‐grown plants had a critical temperature for the rapid rise in Fo that averaged 2·9 °C higher than leaves from ambient CO2‐grown plants, and maintained a higher maximal rate of net CO2 assimilation following heat shock. Given that photosynthesis is considered to be the physiological process most sensitive to high‐temperature damage and that rising atmospheric CO2 content will drive temperature increases in many already stressful environments, this CO2‐induced increase in plant high‐temperature tolerance may have a substantial impact on both the productivity and distribution of many plant species in the 21st century. 相似文献
3.
T. Faria M. Vaz P. Schwanz A. PolIe J. S. Pereira M. M. Chaves 《Plant biology (Stuttgart, Germany)》1999,1(3):365-371
Abstract: Growth in elevated CO2 led to an increase in biomass production per plant as a result of enhanced carbon uptake and lower rates of respiration, compared to ambient CO2-grown plants. No down-regulation of photosynthesis was found after six months of growth under elevated CO2. Photosynthetic rates at 15°C or 35 °C were also higher in elevated than in ambient CO2-grown plants, when measured at their respective CO2 growth condition. Stomata of elevated CO2-grown plants were less responsive to temperature as compared to ambient CO2 plants. The after effect of a heat-shock treatment (4 h at 45 °C in a chamber with 80% of relative humidity and 800–1000 tmol m-2 s-1 photon flux density) on Amax was less in elevated than in ambient CO2-grown plants. At the photochemical level, the negative effect of the heat-shock treatment was slightly more pronounced in ambient than in elevated CO2-grown plants. A greater tolerance to oxidative stress caused by high temperatures in elevated CO2-grown plants, in comparison to ambient CO2 plants, is suggested by the increase in superoxide dismutase activity, after 1 h at 45 °C, as well as its relatively high activity after 2 and 4 h of the heat shock in the elevated CO2-grown plants in contrast with the decrease to residual levels of superoxide dismutase activity in ambient CO2-grown plants immediately after 1 h at 45 °C. The observed increase in catalase after 1 h at 45 °C in both ambient and elevated CO2-grown plants, can be ascribed to the higher rates of photorespiration and respiration under this high temperature. 相似文献
4.
Combined effects of elevated CO2 and air temperature on carbon assimilation of Pinus taeda trees 总被引:1,自引:1,他引:0
R. O. TESKEY 《Plant, cell & environment》1997,20(3):373-380
Branches of 22-year-old loblolly pine (Pinus taeda, L.) trees growing in a plantation were exposed to ambient CO2, ambient + 165 μmol mol?1 CO2 or ambient + 330 μmol mol?1 CO2 concentrations in combination with ambient or ambient + 2°C air temperatures for 3 years. Field measurements in the third year indicated that net carbon assimilation was enhanced in the elevated CO2 treatments in all seasons. On the basis of A/Ci, curves, there was no indication of photosynthetic down-regulation. Branch growth and leaf area also increased significantly in the elevated CO2 treatments. The imposed 2°C increase in air temperature only had slight effects on net assimilation and growth. Compared with the ambient CO2 treatment, rates of net assimilation were ~1·6 times greater in the ambient + 165 μmol mol?1 CO2 treatment and 2·2 times greater in the ambient + 330 μmol mol?1 CO2 treatment. These ratios did not change appreciably in measurements made in all four seasons even though mean ambient air temperatures during the measurement periods ranged from 12·6 to 28·2°C. This indicated that the effect of elevated CO2 concentrations on net assimilation under field conditions was primarily additive. The results also indicated that the effect of elevated CO2 (+ 165 or + 330 μmol mol?1) was much greater than the effect of a 2°C increase in air temperature on net assimilation and growth in this species. 相似文献
5.
Some characteristics of photosynthetic inorganic carbon uptake of a marine macrophytic red alga 总被引:1,自引:1,他引:0
Abstract Some characteristics of photosynthetic inorganic carbon uptake by Palmaria palmata, a marine red macroalga, have been measured under physiological conditions in artificial seawater. The apparent affinity of thallus for CO2 [K1/2(CO2)] at pH 8.0 and 15°C was 21.4±3.0mmol m?3 CO2 under air, and 25.7±70mmol m?3 CO2 under N2. The corresponding values of Vmax were 2.98 ± 0.42 and 3.65±0.87 mmol O2 evolved g Chr?1 s?l. The apparent Km(CO2) of isolated ribulose bisphosphate carboxylase was determined at pH 8.0 and 30 °C to be 30.2 mmol m?3 CO2, and the corresponding value of Vmax was 19.67 μniol CO2 g protein?1 s?1. The CO2 compensation points of the thallus were measured in artificial seawater at pH 8.0 under air and N2, using a gas-chromatographic method. The values were relatively low, rising from 10 cm3 m?3 at 15°C, to 35 cm3 m?3 at 25°C, but were not affected by the O2 concentration. The lack of an effect of O2 on photosynthesis and on compensation point indicates that there is little photorespiratory CO2 loss in this macroalga. The high affinity of the thallus for CO2, and the low CO2 compensation concentrations, are consistent with the occurrence of bicarbonate uptake in this alga. 相似文献
6.
Measurement of the photorespiratory activity of the submerged aquatic plant Myriophyllum spicatum L.
Abstract The CO2 compensation concentrations (points) of leaves of the submerged vascular aquatic plant Myriophyllum spicatum L. were determined in a closed aqueous system at pH 7.0 by a gas chromatographic technique and over the range 10–30deg;C were found to range from 36 to 46 cm3m?3 in medium equilibrated with 21% O2 (0.03 kgm?3), and 25 to 35 cm3m?3 in medium equilibrated with 2% O2 (0.03 kgm?3). The rates of true (TPS) and apparent (APS) photosynthesis of leaves were measured in medium equilibrated with 21% O2 and buffered at pH 7.0, at subsaturating concentrations (12.8–18.8 mmol m?3) of dissolved inorganic carbor. (DIC) containing H14CO3, by determining the initial rates of uptake by the leaves of DIC and 14C-activity from the medium. The rate of photorespiration, the difference between TPS and APS, was 7.0–13.3% of TPS over the range of 10–25°C and rose to 29% of TPS at 35°C. The magnitude of the compensation point of this plant is therefore similar to, but is much less O2-sensitive than, those of C3 plants, and the photorespiratory rate, at DIC concentrations near the CO2 compensation point, is very low compared to that of C3 plants. 相似文献
7.
Arid ecosystems, which occupy about 35% of the Earth's terrestrial surface area, are believed to be among the most responsive to elevated [CO2]. Net ecosystem CO2 exchange (NEE) was measured in the eighth year of CO2 enrichment at the Nevada Desert Free‐Air CO2 Enrichment (FACE) Facility between the months of December 2003–December 2004. On most dates mean daily NEE (24 h) (μmol CO2 m?2 s?1) of ecosystems exposed to elevated atmospheric CO2 were similar to those maintained at current ambient CO2 levels. However, on sampling dates following rains, mean daily NEEs of ecosystems exposed to elevated [CO2] averaged 23 to 56% lower than mean daily NEEs of ecosystems maintained at ambient [CO2]. Mean daily NEE varied seasonally across both CO2 treatments, increasing from about 0.1 μmol CO2 m?2 s?1 in December to a maximum of 0.5–0.6 μmol CO2 m?2 s?1 in early spring. Maximum NEE in ecosystems exposed to elevated CO2 occurred 1 month earlier than it did in ecosystems exposed to ambient CO2, with declines in both treatments to lowest seasonal levels by early October (0.09±0.03 μmol CO2 m?2 s?1), but then increasing to near peak levels in late October (0.36±0.08 μmol CO2 m?2 s?1), November (0.28±0.03 μmol CO2 m?2 s?1), and December (0.54±0.06 μmol CO2 m?2 s?1). Seasonal patterns of mean daily NEE primarily resulted from larger seasonal fluctuations in rates of daytime net ecosystem CO2 uptake which were closely tied to plant community phenology and precipitation. Photosynthesis in the autotrophic crust community (lichens, mosses, and free‐living cyanobacteria) following rains were probably responsible for the high NEEs observed in January, February, and late October 2004 when vascular plant photosynthesis was low. Both CO2 treatments were net CO2 sinks in 2004, but exposure to elevated CO2 reduced CO2 sink strength by 30% (positive net ecosystem productivity=127±17 g C m?2 yr?1 ambient CO2 and 90±11 g C m?2 yr?1 elevated CO2, P=0.011). This level of net C uptake rivals or exceeds levels observed in some forested and grassland ecosystems. Thus, the decrease in C sequestration seen in our study under elevated CO2– along with the extensive coverage of arid and semi‐arid ecosystems globally – points to a significant drop in global C sequestration potential in the next several decades because of responses of heretofore overlooked dryland ecosystems. 相似文献
8.
Interactive effects of elevated CO2 and soil fertility on isoprene emissions from Quercus robur 总被引:2,自引:0,他引:2
Malcolm Possell James Heath† C. Nicholas Hewitt Edward Ayres† Gerhard Kerstiens† 《Global Change Biology》2004,10(11):1835-1843
The effects of global change on the emission rates of isoprene from plants are not clear. A factor that can influence the response of isoprene emission to elevated CO2 concentrations is the availability of nutrients. Isoprene emission rate under standard conditions (leaf temperature: 30°C, photosynthetically active radiation (PAR): 1000 μmol photons m?2 s?1), photosynthesis, photosynthetic capacity, and leaf nitrogen (N) content were measured in Quercus robur grown in well‐ventilated greenhouses at ambient and elevated CO2 (ambient plus 300 ppm) and two different soil fertilities. The results show that elevated CO2 enhanced photosynthesis but leaf respiration rates were not affected by either the CO2 or nutrient treatments. Isoprene emission rates and photosynthetic capacity were found to decrease with elevated CO2, but an increase in nutrient availability had the converse effect. Leaf N content was significantly greater with increased nutrient availability, but unaffected by CO2. Isoprene emission rates measured under these conditions were strongly correlated with photosynthetic capacity across the range of different treatments. This suggests that the effects of CO2 and nutrient levels on allocation of carbon to isoprene production and emission under near‐saturating light largely depend on the effects on photosynthetic electron transport capacity. 相似文献
9.
The effect of temperature and oxygen on the CO2 compensation point of the marine alga Ulva lactuca 总被引:3,自引:3,他引:0
BRIAN COLMAN 《Plant, cell & environment》1984,7(8):619-621
Abstract The CO2 compensation point of Ulva lactuca frond sections has been measured in artificial seawater using a sensitive gas-chromatographic method. Under nitrogen the compensation point remained relatively constant at 3–6 cm3 m−3 at temperatures from 10 to 30°C while in air-saturated medium (0.3 kg m−3 O2) the compensation point rose from 5 cm3 m−3 at 10°C to 11 cm3 m−3 at 30°C. These responses of the compensation point to temperature and oxygen concentration indicate that there is little photorespiratory CO2 loss in this marine macroalga, and the low values of these compensation points indicate that inorganic carbon is actively accumulated by the plant. 相似文献
10.
H. GRIFFITHS 《Plant, cell & environment》1988,11(7):603-611
Abstract The regulation of crassulacean acid metabolism (CAM) under controlled environmental conditions has been investigated for two tropical epiphytes, relating plant water and carbon balance to growth form and habitat preference under natural conditions. Aechmea fendleri is restricted to wet, upper montane regions of Trinidad, while A. nudicaulis has a wider distribution extending into more arid regions of the island. Morphological characteristics of these plants are related to habitat preference in terms of leaf succulence (0.44 and 0.94 kg m?2 for the two species respectively) and a distinct layer of water storage parenchyma in A. nudicaulis In contrast, the thinner leaves of A. fendleri contain little water-storage parenchyma and less chlorenchyma per unit area, but the plants have a more open leaf rosette. The two species differ in expression of CAM, since the proportion of respiratory CO2 recycled as part of CAM had been found to be much lower in A. fendleri This study compared the efficiency of water use and role of respiratory CO2 recycling under two PAR regimes (300 and 120 μnol m?2 s?1) and three night temperatures (12, 18 and 25 °C). Dark CO2 uptake rates for both species were comparable to plants in the field (maximum of 2.3 ± 0.2 μmol m?2s?1± SD, n= 3). Total net CO2 uptake at night increased on leaf area basis with temperature for both species under higher PAR, although under the low PAR regime CO2 uptake was maximal at 18 °C. Water-use efficiency (WUE) increased at 18 °C and 25 °C during dark CO2 uptake (Phase I) and also during late afternoon photosynthesis (Phase IV) in both species. For A. fendleri, dawn to dusk changes in titrable acidity (ΔH +) were similar under high and low PAR, although ΔH+ was correlated to night temperature and PAR in A. nudicaulis. The proportion of ΔH+ derived from respiratory CO2 also varied with experimental conditions. Thus percentage recycling was lower in A. fendleri under high PAR (0–10%), but was only reduced at 18 °C under low PAR. Recycling by A. nudicaulis ranged from 32–42% under high PAR, but was also reduced to 6% under low PAR at 18 °C; at 12 °C and 25 °C, recycling was 37% and 52% respectively. Previous studies have suggested a relationship between the proportion of recycling and degree of water stress. This study indicated that CAM as a CO2 concentrating mechanism regulates both water-use efficiency and plant carbon balance in these epiphytes, in response to PAR and night temperature. However, the precise relationship between respiratory processes and the balance between external and internal sources of CO2 is as yet unresolved. 相似文献
11.
D. ZHAO K. R. REDDY V. G. KAKANI J. J. READ & J. H. SULLIVAN 《Plant, cell & environment》2003,26(5):771-782
Better understanding of crop responses to projected changes in climate is an important requirement. An experiment was conducted in sunlit, controlled environment chambers known as soil–plant–atmosphere–research units to determine the interactive effects of atmospheric carbon dioxide concentration [CO2] and ultraviolet‐B (UV‐B) radiation on cotton (Gossypium hirsutum L.) growth, development and leaf photosynthetic characteristics. Six treatments were used, comprising two levels of [CO2] (360 and 720 µmol mol?1) and three levels of 0 (control), 7.7 and 15.1 kJ m?2 d?1 biologically effective UV‐B radiations within each CO2 level. Treatments were imposed for 66 d from emergence until 3 weeks after the first flower stage. Plants grown in elevated [CO2] had greater leaf area and higher leaf photosynthesis, non‐structural carbohydrates, and total biomass than plants in ambient [CO2]. Neither dry matter partitioning among plant organs nor pigment concentrations was affected by elevated [CO2]. On the other hand, high UV‐B (15.1 kJ m?2 d?1) radiation treatment altered growth resulting in shorter stem and branch lengths and smaller leaf area. Shorter plants at high UV‐B radiation were related to internode lengths rather than the number of mainstem nodes. Fruit dry matter accumulation was most sensitive to UV‐B radiation due to fruit abscission. Even under 7.7 kJ m?2 d?1 of UV‐B radiation, fruit dry weight was significantly lower than the control although total biomass and leaf photosynthesis did not differ from the control. The UV‐B radiation of 15.1 kJ m?2 d?1 reduced both total (43%) and fruit (88%) dry weights due to smaller leaf area and lower leaf net photosynthesis. Elevated [CO2] did not ameliorate the adverse effects of UV‐B radiation on cotton growth and physiology, particularly the boll retention under UV‐B stress. 相似文献
12.
P. A. SCHOLEFIELD K. J. DOICK B. M. J. HERBERT C. N. S HEWITT J.‐P. SCHNITZLER P. PINELLI F. LORETO 《Plant, cell & environment》2004,27(4):393-401
Isoprene basal emission (the emission of isoprene from leaves exposed to a light intensity of 1000 µmol m?2 s?1 and maintained at a temperature of 30 °C) was measured in Phragmites australis plants growing under elevated CO2 in the Bossoleto CO2 spring at Rapolano Terme, Italy, and under ambient CO2 at a nearby control site. Gas exchange and biochemical measurements were concurrently taken. Isoprene emission was lower in the plants growing at elevated CO2 than in those growing at ambient CO2. Isoprene emission and isoprene synthase activity (IsoS) were very low in plants growing at the bottom of the spring under very rich CO2 and increased at increasing distance from the spring (and decreasing CO2 concentration). Distance from the spring did not significantly affect photosynthesis making it therefore unlikely that there is carbon limitation to isoprene formation. The isoprene emission rate was very quickly reduced after rapid switches from elevated to ambient CO2 in the gas‐exchange cuvette, whereas it increased when switching from ambient to elevated CO2. The rapidity of the response may be consistent with post‐translational modifications of enzymes in the biosynthetic pathway of isoprene formation. Reduction of IsoS activity is interpreted as a long‐term response. Basal emission of isoprene was not constant over the day but showed a diurnal course opposite to photosynthesis, with a peak during the hottest hours of the day, independent of stomatal conductance and probably dependent on external air temperature or temporary reduction of CO2 concentration. The present experiments show that basal emission rate of isoprene is likely to be reduced under future elevated CO2 levels and allow improvement in the modelling of future isoprene emission rates. 相似文献
13.
Clonal plants of white clover (Trifolium repens L.), grown singly in pots of Perlite and solely dependent for nitrogen on root nodule N2 fixation, were maintained in controlled environments which provided four environments: 18/13 °C day/night temperature at 340 and 680 μmol mol?1 CO2 and 20·5/15·5°C day/night temperature at 340 and 680 μmol mol?1 CO2. The daylength was 12 h and the photon flux density 500±25 μmol m?2 s?1 (PFD). All plants were defoliated for about 80d, nominally every alternate day, to leave the youngest expanded leaf intact on 50% of stolons, plus expanding leaves (simulated grazing). Elevated CO2 increased the yield of biomass removed at defoliation by a constant 45% during the second 40d of the experiment and by a varying amount in the first half of the experiment. Elevated temperature had little effect on biomass yield. Nitrogen, as a proportion of the harvested biomass, was only fractionally affected by elevated CO2 or temperature. In contrast, N2 fixation increased in concert with the promoting effect of elevated CO2 on biomass production. The increased yield of biomass harvested in 680 μmol mol?1 CO2 was primarily due to the early development and continued maintenance of more stolons. However, the stolons of plants grown in elevated CO2 also developed leaves which were heavier and slightly larger in area than their counterparts in ambient CO2. The conclusion is that, when white clover plants are maintained at constant mass by simulated grazing, they continue to respond to elevated CO2 in terms of a sustained increase in biomass production. 相似文献
14.
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
15.
JAANA K. HAAPALA SAMI K. MÖRSKY† SANNA SAARNIO RIIKKA RINNAN‡ HANNE SUOKANERVA§ ESKO KYRÖ§ KIRSI LATOLA¶ PERTTI J. MARTIKANEN† TOINI HOLOPAINEN† JOUKO SILVOLA 《Global Change Biology》2009,15(4):943-954
The effect of elevated UV‐B radiation on CO2 exchange of a natural flark fen was studied in open‐field conditions during 2003–2005. The experimental site was located in Sodankylä in northern Finland (67°22′N, 26°38′E, 179 m a.s.l.). Altogether 30 study plots, each 120 cm × 120 cm in size, were randomly distributed between three treatments (n=10): ambient control, UV‐A control and UV‐B treatment. The UV‐B‐treated plots were exposed to elevated UV‐B radiation level for three growing seasons. The instantaneous net ecosystem CO2 exchange (NEE) and dark respiration (RTOT) were measured during the growing season using a closed chamber method. The wintertime CO2 emissions were estimated using a gradient technique by analyzing the CO2 concentration in the snow pack. In addition to the instantaneous CO2 exchange, the seasonal CO2 balances during the growing seasons were modeled using environmental data measured at the site. In general, the instantaneous NEE at light saturation was slightly higher in the UV‐B treatment compared with the ambient control, but the gross photosynthesis was unaffected by the exposure. The RTOT was significantly lower under elevated UV‐B in the third study year. The modeled seasonal (June–September) CO2 balance varied between the years depending on the ground water level and temperature conditions. During the driest year, the seasonal CO2 balance was negative (net release of CO2) in the ambient control and the UV‐B treatment was CO2 neutral. During the third year, the seasonal CO2 uptake was 43±36 g CO2‐C m−2 in the ambient control and 79±45 g CO2‐C m−2 in the UV‐B treatment. The results suggest that the long‐term exposure to high UV‐B radiation levels may slightly increase the CO2 accumulation to fens resulting from a decrease in microbial activity in peat. However, it is unlikely that the predicted development of the level of UV‐B radiation would significantly affect the CO2 balance of fen ecosystems in future. 相似文献
16.
B. J. Mulholland J. Craigon C. R. Black J. J. Colls J. Atherton† G. Landon 《Global Change Biology》1998,4(2):121-130
Spring wheat cv. Minaret was grown to maturity under three carbon dioxide (CO2) and two ozone (O3) concentrations in open-top chambers (OTC). Green leaf area index (LAI) was increased by elevated CO2 under ambient O3 conditions as a direct result of increases in tillering, rather than individual leaf areas. Yellow LAI was also greater in the 550 and 680 μmol mol–1 CO2 treatments than in the chambered ambient control; individual leaves on the main shoot senesced more rapidly under 550 μmol mol–1 CO2, but senescence was delayed at 680 μmol mol–1 CO2. Fractional light interception (f) during the vegetative period was up to 26% greater under 680 μmol mol–1 CO2 than in the control treatment, but seasonal accumulated intercepted radiation was only increased by 8%. As a result of greater carbon assimilation during canopy development, plants grown under elevated CO2 were taller at anthesis and stem and ear biomass were 27 and 16% greater than in control plants. At maturity, yield was 30% greater in the 680 μmol mol–1 CO2 treatment, due to a combination of increases in the number of ears per m–2, grain number per ear and individual grain weight (IGW). Exposure to a seasonal mean (7 h d–1) of 84 nmol mol–1 O3 under ambient CO2 decreased green LAI and increased yellow LAI, thereby reducing both f and accumulated intercepted radiation by ≈ 16%. Individual leaves senesced completely 7–28 days earlier than in control plants. At anthesis, the plants were shorter than controls and exhibited reductions in stem and ear biomass of 15 and 23%. Grain yield at maturity was decreased by 30% due to a combination of reductions in ear number m–2, the numbers of grains per spikelet and per ear and IGW. The presence of elevated CO2 reduced the rate of O3-induced leaf senescence and resulted in the maintenance of a higher green LAI during vegetative growth under ambient CO2 conditions. Grain yields at maturity were nevertheless lower than those obtained in the corresponding elevated CO2 treatments in the absence of elevated O3. Thus, although the presence of elevated CO2 reduced the damaging impact of ozone on radiation interception and vegetative growth, substantial yield losses were nevertheless induced. These data suggest that spring wheat may be susceptible to O3-induced injury during anthesis irrespective of the atmospheric CO2 concentration. Possible deleterious mechanisms operating through effects on pollen viability, seed set and the duration of grain filling are discussed. 相似文献
17.
NMR imaging of root water distribution in intact Vicia faba L plants in elevated atmospheric CO2 总被引:1,自引:1,他引:0
The effect of elevated atmospheric CO2 on water distribution in the intact roots of Vicia faba L. bean seedlings grown in natural soil was studied noninvasively with proton (1H) nuclear magnetic resonance (NMR) imaging. Exposure of 24-d-old plants to atmospheric CO2-enriched air at 650 cm3 m?3 produced significant increases in water imaged in upper roots, hypogeal cotyledons and lower stems in response to a short-term drying-stress cycle. Above ground, drying produced negligible stem shrinkage and stomatal resistance was unchanged. In contrast, the same drying cycle caused significant depletion of water imaged in the same upper root structures in control plants subject to ambient CO2 (350 m3 m?3), and stem shrinkage and increased stomatal resistance. The results suggest that inhibition of transpiration caused by elevated CO2 does not necessarily result in attenuation of water transport from lower root structures. Inhibition of water loss from upper roots and lower stem in elevated CO2 environments may be a mitigating factor in assessing deleterious effects of greenhouse changes on crops during periods of dry climate. 相似文献
18.
P. C. Mielnick W. A. Dugas H. B. Johnson† H. W. Polley† J. Sanabria 《Global Change Biology》2001,7(7):747-754
Increasing atmospheric CO2 concentrations may have a profound effect on the structure and function of plant communities. A previously grazed, central Texas grassland was exposed to a 200‐µmol mol?1 to 550 µmol mol?1 CO2 gradient from March to mid‐December in 1998 and 1999 using two, 60‐m long, polyethylene‐ covered chambers built directly onto the site. One chamber was operated at subambient CO2 concentrations (200–360 µmol mol?1 daytime) and the other was regulated at superambient concentrations (360–550 µmol mol?1). Continuous CO2 gradients were maintained in each chamber by photosynthesis during the day and respiration at night. Net ecosystem CO2 flux and end‐of‐year biomass were measured in each of 10, 5‐m long sections in each chamber. Net CO2 fluxes were maximal in late May (c. day 150) in 1998 and in late August in 1999 (c. day 240). In both years, fluxes were near zero and similar in both chambers at the beginning and end of the growing season. Average daily CO2 flux in 1998 was 13 g CO2 m?2 day?1 in the subambient chamber and 20 g CO2 m?2 day?1 in the superambient chamber; comparable averages were 15 and 26 g CO2 m?2 day?1 in 1999. Flux was positively and linearly correlated with end‐of‐year above‐ground biomass but flux was not linearly correlated with CO2 concentration; a finding likely to be explained by inherent differences in vegetation. Because C3 plants were the dominant functional group, we adjusted average daily flux in each section by dividing the flux by the average percentage C3 cover. Adjusted fluxes were better correlated with CO2 concentration, although scatter remained. Our results indicate that after accounting for vegetation differences, CO2 flux increased linearly with CO2 concentration. This trend was more evident at subambient than superambient CO2 concentrations. 相似文献
19.
Masabumi Komatsu Hiroyuki Tobita Makoto Watanabe Kenichi Yazaki Takayoshi Koike Mitsutoshi Kitao 《Physiologia plantarum》2013,147(2):159-168
To determine the effects of elevated CO2 concentration ([CO2]) on the temperature‐dependent photosynthetic properties, we measured gas exchange and chlorophyll fluorescence at various leaf temperatures (15, 20, 25, 30, 35 and 40°C) in 1‐year‐old seedlings of the Japanese white birch (Betula platyphylla var. japonica), grown in a phytotron under natural daylight at two [CO2] levels (ambient: 400 µmol mol?1 and elevated: 800 µmol mol?1) and limited N availability (90 mg N plant?1). Plants grown under elevated [CO2] exhibited photosynthetic downregulation, indicated by a decrease in the carboxylation capacity of Rubisco. At temperatures above 30°C, the net photosynthetic rates of elevated‐CO2‐grown plants exceeded those grown under ambient [CO2] when compared at their growth [CO2]. Electron transport rates were significantly lower in elevated‐CO2‐grown plants than ambient‐CO2‐grown ones at temperatures below 25°C. However, no significant difference was observed in the fraction of excess light energy [(1 ? qP)× Fv′/Fm′] between CO2 treatments across the temperature range. The quantum yield of regulated non‐photochemical energy loss was significantly higher in elevated‐CO2‐grown plants than ambient, when compared at their respective growth [CO2] below 25°C. These results suggest that elevated‐CO2‐induced downregulation might not exacerbate the temperature‐dependent susceptibility to photoinhibition, because reduced energy consumption by electron transport was compensated for by increased thermal energy dissipation at low temperatures. 相似文献
20.
Two mangrove species, Rhizophora apiculata and R. stylosa, were grown for 14 weeks in a multifactorial combination of salinity (125 and 350 mol m?3 NaCl), humidity (43 and 86% relative humidity at 30°C) and atmospheric CO2 concentration (340 and 700 cm3 m?3). Under ambient [CO2], growth responses to different combinations of salinity and humidity were consistent with interspecific differences in distribution along natural gradients of salinity and aridity in northern Australia. Elevated [CO2] had little effect on relative growth rate when it was limited by salinity but stimulated growth when limited by humidity. Both species benefited most from elevated [CO2] under relatively low salinity conditions in which growth was vigorous, but relative growth rate was enhanced more in the less salt-tolerant and more rapidly growing species, R. apiculata. Changes in both net assimilation rate and leaf area ratio contributed to changes in relative growth rates under elevated [CO2], with leaf area ratio increasing with decrease in humidity. Increase in water use efficiency under elevated [CO2] occurred with increase, decrease or no change in evaporation rates; water use characteristics which depended on both the species and the growth conditions. In summary, elevated [CO2] is unlikely to increase salt tolerance, but could alter competitive rankings of species along salinity × aridity gradients. 相似文献