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1.
Twenty genotypes of Jatropha collected from diverse eco-geographic regions from the states of Chhattisgarh (3), Andhra Pradesh (12), Rajasthan (4) and Uttarakhand (1) of India were subjected to elevated CO 2 conditions. All the genotypes showed significant difference ( p < 0.05 and 0.01) in the phenotypic traits in both the environments (elevated and ambient) and genotype x environment interaction. Among the physiological traits recorded, maximum photosynthetic rate was observed in IC565048 (48.8 μmol m −2 s −1) under ambient controlled conditions while under elevated conditions maximum photosynthetic rate was observed in IC544678 (41.3 μmol m −2 s −1), and there was no significant difference in the genotype x environment interaction. Stomatal conductance (Gs) emerged as the key factor as it recorded significant difference among the genotypes, between the environments and also genotype x environment interaction. The Gs and transpiration (E) recorded a significant decline in the genotypes under the elevated CO 2 condition over the ambient control. Under elevated CO 2 conditions, the minimum values recorded for Gs and E were 0.03 mmol m −2 s −1 and 0.59 mmol m −2 s −1 respectively in accession IC565039, while the maximum values for Gs and E were 1.8 mmol m −2 s −1 and 11.5 mmol m −2 s −1 as recorded in accession IC544678. The study resulted in the identification of potential climate ready genotypes viz. IC471314, IC544654, IC541634, IC544313, and IC471333 for future use. 相似文献
2.
The ability of 21 C 3 and C 4 monocot and dicot species to rapidly export newly fixed C in the light at both ambient and enriched CO 2 levels was compared. Photosynthesis and concurrent export rates were estimated during isotopic equilibrium of the transport sugars using a steady-state 14CO 2-labeling procedure. At ambient CO 2 photosynthesis and export rates for C 3 species were 5 to 15 and 1 to 10 μmol C m −2 s −1, respectively, and 20 to 30 and 15 to 22 μmol C m −2 s −1, respectively, for C 4 species. A linear regression plot of export on photosynthesis rate of all species had a correlation coefficient of 0.87. When concurrent export was expressed as a percentage of photosynthesis, several C 3 dicots that produced transport sugars other than Suc had high efflux rates relative to photosynthesis, comparable to those of C 4 species. At high CO 2 photosynthetic and export rates were only slightly altered in C 4 species, and photosynthesis increased but export rates did not in all C 3 species. The C 3 species that had high efflux rates relative to photosynthesis at ambient CO 2 exported at rates comparable to those of C 4 species on both an absolute basis and as a percentage of photosynthesis. At ambient CO 2 there were strong linear relationships between photosynthesis, sugar synthesis, and concurrent export. However, at high CO 2 the relationships between photosynthesis and export rate and between sugar synthesis and export rate were not as strong because sugars and starch were accumulated. 相似文献
3.
Mass-spectrometric disequilibrium analysis was applied to investigate CO 2 uptake and HCO 3− transport in cells and chloroplasts of the microalgae Dunaliella tertiolecta and Chlamydomonas reinhardtii, which were grown in air enriched with 5% (v/v) CO 2 (high-Ci cells) or in ambient air (low-Ci cells). High- and low-Ci cells of both species had the capacity to transport CO 2 and HCO 3−, with maximum rates being largely unaffected by the growth conditions. In high- and low-Ci cells of D. tertiolecta, HCO 3− was the dominant inorganic C species taken up, whereas HCO 3− and CO 2 were used at similar rates by C. reinhardtii. The apparent affinities of HCO 3− transport and CO 2 uptake increased 3- to 9-fold in both species upon acclimation to air. Photosynthetically active chloroplasts isolated from both species were able to transport CO 2 and HCO 3−. For chloroplasts from C. reinhardtii, the concentrations of HCO 3− and CO 2 required for half-maximal activity declined from 446 to 33 μm and 6.8 to 0.6 μm, respectively, after acclimation of the parent cells to air; the corresponding values for chloroplasts from D. tertiolecta decreased from 203 to 58 μm and 5.8 to 0.5 μm, respectively. These results indicate the presence of inducible high-affinity HCO 3− and CO 2 transporters at the chloroplast envelope membrane. 相似文献
4.
Phosphorus deficiency was induced in sugar beet plants ( Beta vulgaris L. var. F5855441), cultured hydroponically under standardized environmental conditions, by removal of phosphorus from the nutrient supply at the ten leaf stage 28 days after germination. CO 2 and water vapor exchange rates of individual attached leaves were determined at intervals after P cutoff. Leaves grown with an adequate nutrient supply attained net rates of photosynthetic CO 2 fixation of 125 ng CO 2 cm −2 sec −1 at saturating irradiance, 25 C, and an ambient CO 2 concentration of about 250 μl l −1. After P cutoff, leaf phosphorus concentrations decreased as did net rates of photosynthetic CO 2 uptake, photorespiratory evolution of CO 2 into CO 2-free air, and dark respiration, so that 30 days after cutoff these rates were about one-third of the control rates. The decrease in photosynthetic rates during the first 15 days after cutoff was associated with increased mesophyll resistance ( rm) which increased from 2.4 to 4.9 sec cm −1, while from 15 to 30 days there was an increase in leaf (mainly stomatal) diffusion resistance ( rl′) from 0.3 to 0.9 sec cm −1, as well as further increases in rm to 8.5 sec cm −1. Leaf diffusion resistance ( rl′) was increased greatly by low P at low but not at high irradiance, rl′ for plants at low P reaching values as high as 9 sec cm −1. 相似文献
5.
Thalli discs of the marine macroalga Ulva lactuca were given inorganic carbon in the form of HCO 3−, and the progression of photosynthetic O 2 evolution was followed and compared with predicted O 2 evolution as based on calculated external formation of CO 2 (extracellular carbonic anhydrase was not present in this species) and its carboxylation (according to the Km(CO 2) of ribulose-1,5-bisphosphate carboxylase/oxygenase), at two different pHs, assuming a photosynthetic quotient of 1. The Km(inorganic carbon) was some 2.5 times lower at pH 5.6 than at the natural seawater pH of 8.2, whereas Vmax was similar under the two conditions, indicating that the unnaturally low pH per se had no adverse effect on U. lactuca's photosynthetic performance. These results, therefore, could be evaluated with regard to differential CO 2 and HCO 3− utilization. The photosynthetic performance observed at the lower pH largely followed that predicted, with a slight discrepancy probably reflecting a minor diffusion barrier to CO 2 uptake. At pH 8.2, however, dehydration rates were too slow to supply CO 2 for the measured photosynthetic response. Given the absence of external carbonic anhydrase activity, this finding supports the view that HCO 3− transport provides higher than external concentrations of CO 2 at the ribulose-1,5-bisphosphate carboxylase/oxygenase site. Uptake of HCO 3− by U. lactuca was further indicated by the effects of potential inhibitors at pH 8.2. The alleged band 3 membrane anion exchange protein inhibitor 4,4′-diisothiocyanostilbene-2,2′disulphonate reduced photosynthetic rates only when HCO 3− (but not CO 2) could be the extracellular inorganic carbon form taken up. A similar, but less drastic, HCO 3−-competitive inhibition of photosynthesis was obtained with Kl and KNO 3. It is suggested that, under ambient conditions, HCO 3− is transported into cells at defined sites either via facilitated diffusion or active uptake, and that such transport is the basis for elevated internal [CO 2] at the site of ribulose-1,5-bisphosphate carboxylase/oxygenase carboxylation. 相似文献
6.
Effects of extremely high carbon dioxide (CO 2) concentrations on soil microbial communities and associated processes are largely unknown. We studied a wetland area affected by spots of subcrustal CO 2
degassing (mofettes) with focus on anaerobic autotrophic methanogenesis and acetogenesis because the pore gas phase was largely hypoxic. Compared with a reference soil, the mofette was more acidic (ΔpH ∼0.8), strongly enriched in organic carbon (up to 10 times), and exhibited lower prokaryotic diversity. It was dominated by methanogens and subdivision 1
Acidobacteria, which likely thrived under stable hypoxia and acidic pH. Anoxic incubations revealed enhanced formation of acetate and methane (CH 4) from hydrogen (H 2) and CO 2
consistent with elevated CH 4
and acetate levels in the mofette soil.
13CO 2
mofette soil incubations showed high label incorporations with ∼512 ng
13C g (dry weight (dw)) soil −1 d −1
into the bulk soil and up to 10.7 ng
13C g (dw) soil −1 d −1
into almost all analyzed bacterial lipids. Incorporation of CO 2-derived carbon into archaeal lipids was much lower and restricted to the first 10 cm of the soil. DNA-SIP analysis revealed that acidophilic methanogens affiliated with
Methanoregulaceae
and hitherto unknown acetogens appeared to be involved in the chemolithoautotrophic utilization of
13CO 2. Subdivision 1
Acidobacteriaceae
assimilated
13CO 2
likely via anaplerotic reactions because
Acidobacteriaceae
are not known to harbor enzymatic pathways for autotrophic CO 2
assimilation. We conclude that CO 2-induced geochemical changes promoted anaerobic and acidophilic organisms and altered carbon turnover in affected soils. 相似文献
7.
Background and Aims Plants growing under elevated atmospheric CO 2 concentrations often have reduced stomatal conductance and subsequently increased leaf temperature. This study therefore tested the hypothesis that under long-term elevated CO 2 the temperature optima of photosynthetic processes will shift towards higher temperatures and the thermostability of the photosynthetic apparatus will increase.Methods The hypothesis was tested for saplings of broadleaved Fagus sylvatica and coniferous Picea abies exposed for 4–5 years to either ambient (AC; 385 µmol mol −1) or elevated (EC; 700 µmol mol −1) CO 2 concentrations. Temperature response curves of photosynthetic processes were determined by gas-exchange and chlorophyll fluorescence techniques.Key Results Initial assumptions of reduced light-saturated stomatal conductance and increased leaf temperatures for EC plants were confirmed. Temperature response curves revealed stimulation of light-saturated rates of CO 2 assimilation ( Amax) and a decline in photorespiration ( RL) as a result of EC within a wide temperature range. However, these effects were negligible or reduced at low and high temperatures. Higher temperature optima ( Topt) of Amax, Rubisco carboxylation rates ( VCmax) and RL were found for EC saplings compared with AC saplings. However, the shifts in Topt of Amax were instantaneous, and disappeared when measured at identical CO 2 concentrations. Higher values of Topt at elevated CO 2 were attributed particularly to reduced photorespiration and prevailing limitation of photosynthesis by ribulose-1,5-bisphosphate (RuBP) regeneration. Temperature response curves of fluorescence parameters suggested a negligible effect of EC on enhancement of thermostability of photosystem II photochemistry.Conclusions Elevated CO 2 instantaneously increases temperature optima of Amax due to reduced photorespiration and limitation of photosynthesis by RuBP regeneration. However, this increase disappears when plants are exposed to identical CO 2 concentrations. In addition, increased heat-stress tolerance of primary photochemistry in plants grown at elevated CO 2 is unlikely. The hypothesis that long-term cultivation at elevated CO 2 leads to acclimation of photosynthesis to higher temperatures is therefore rejected. Nevertheless, incorporating acclimation mechanisms into models simulating carbon flux between the atmosphere and vegetation is necessary. 相似文献
8.
Potato plants ( Solanum tuberosum L. cv. Bintje) were grown to maturity in open-top chambers under three carbon dioxide (CO 2; ambient and 24 h d −1 seasonal mean concentrations of 550 and 680 μmol mol −1) and two ozone levels (O 3; ambient and an 8 h d −1 seasonal mean of 50 nmol mol −1). Chlorophyll content, photosynthetic characteristics, and stomatal responses were determined to test the hypothesis that elevated atmospheric CO 2 may alleviate the damaging influence of O 3 by reducing uptake by the leaves. Elevated O 3 had no detectable effect on photosynthetic characteristics, leaf conductance, or chlorophyll content, but did reduce SPAD values for leaf 15, the youngest leaf examined. Elevated CO 2 also reduced SPAD values for leaf 15, but not for older leaves; destructive analysis confirmed that chlorophyll content was decreased. Leaf conductance was generally reduced by elevated CO 2, and declined with time in the youngest leaves examined, as did assimilation rate ( A). A generally increased under elevated CO 2, particularly in the older leaves during the latter stages of the season, thereby increasing instantaneous transpiration efficiency. Exposure to elevated CO 2 and/or O 3 had no detectable effect on dark-adapted fluorescence, although the values decreased with time. Analysis of the relationships between assimilation rate and intercellular CO 2 concentration and photosynthetically active photon flux density showed there was initially little treatment effect on CO 2-saturated assimilation rates for leaf 15. However, the values for plants grown under 550 μmol mol −1 CO 2 were subsequently greater than in the ambient and 680 μmol mol −1 treatments, although the beneficial influence of the former treatment declined sharply towards the end of the season. Light-saturated assimilation was consistently greater under elevated CO 2, but decreased with time in all treatments. The values decreased sharply when leaves grown under elevated CO 2 were measured under ambient CO 2, but increased when leaves grown under ambient CO 2 were examined under elevated CO 2. The results obtained indicate that, although elevated CO 2 initially increased assimilation and growth, these beneficial effects were not necessarily sustained to maturity as a result of photosynthetic acclimation and the induction of earlier senescence. 相似文献
9.
The biodegradability of aerial material from a C4 plant, sorghum grown under ambient (345 µmol mol –1) and elevated (700 µmol mol –1) atmospheric CO 2 concentrations were compared by measuring soil respiratory activity. Initial daily respiratory activity (measured over 10 h per day) increased four fold from 110 to 440 cm 3 CO 2 100g dry weight soil –1 in soils amended with sorghum grown under either elevated or ambient CO 2. Although soil respiratory activity decreased over the following 30 days, respiration remained significantly higher (t-test; p>0.05) in soils amended with sorghum grown under elevated CO 2 concentrations. Analysis of the plant material revealed no significant differences in C:N ratios between sorghum grown under elevated or ambient CO 2. The reason for the differences in soil respiratory activity have yet to be elucidated. However if this trend is repeated in natural ecosystems, this may have important implications for C and N cycling. 相似文献
10.
Ocean acidification (OA) due to atmospheric CO 2 rise is expected to influence marine primary productivity. In order to investigate the interactive effects of OA and light changes on diatoms, we grew Phaeodactylum tricornutum, under ambient (390 ppmv; LC) and elevated CO 2 (1000 ppmv; HC) conditions for 80 generations, and measured its physiological performance under different light levels (60 µmol m −2 s −1, LL; 200 µmol m −2 s −1, ML; 460 µmol m −2 s −1, HL) for another 25 generations. The specific growth rate of the HC-grown cells was higher (about 12–18%) than that of the LC-grown ones, with the highest under the ML level. With increasing light levels, the effective photochemical yield of PSII (F v′/F m′) decreased, but was enhanced by the elevated CO 2, especially under the HL level. The cells acclimated to the HC condition showed a higher recovery rate of their photochemical yield of PSII compared to the LC-grown cells. For the HC-grown cells, dissolved inorganic carbon or CO 2 levels for half saturation of photosynthesis (K 1/2 DIC or K 1/2 CO 2) increased by 11, 55 and 32%, under the LL, ML and HL levels, reflecting a light dependent down-regulation of carbon concentrating mechanisms (CCMs). The linkage between higher level of the CCMs down-regulation and higher growth rate at ML under OA supports the theory that the saved energy from CCMs down-regulation adds on to enhance the growth of the diatom. 相似文献
11.
It is vital to understand responses of soil microorganisms to predicted climate changes, as these directly control soil carbon (C) dynamics. The rate of turnover of soil organic carbon is mediated by soil microorganisms whose activity may be affected by climate change. After one year of multifactorial climate change treatments, at an undisturbed temperate heathland, soil microbial community dynamics were investigated by injection of a very small concentration (5.12 µg C g −1 soil) of 13C-labeled glycine ( 13C 2, 99 atom %) to soils in situ. Plots were treated with elevated temperature (+1°C, T), summer drought (D) and elevated atmospheric carbon dioxide (510 ppm [CO2]), as well as combined treatments (TD, TCO2, DCO2 and TDCO2). The 13C enrichment of respired CO 2 and of phospholipid fatty acids (PLFAs) was determined after 24 h. 13C-glycine incorporation into the biomarker PLFAs for specific microbial groups (Gram positive bacteria, Gram negative bacteria, actinobacteria and fungi) was quantified using gas chromatography-combustion-stable isotope ratio mass spectrometry (GC-C-IRMS).Gram positive bacteria opportunistically utilized the freshly added glycine substrate, i.e. incorporated 13C in all treatments, whereas fungi had minor or no glycine derived 13C-enrichment, hence slowly reacting to a new substrate. The effects of elevated CO 2 did suggest increased direct incorporation of glycine in microbial biomass, in particular in G + bacteria, in an ecosystem subjected to elevated CO 2. Warming decreased the concentration of PLFAs in general. The FACE CO 2 was 13C-depleted (δ 13C = 12.2‰) compared to ambient (δ 13C = ∼−8‰), and this enabled observation of the integrated longer term responses of soil microorganisms to the FACE over one year. All together, the bacterial (and not fungal) utilization of glycine indicates substrate preference and resource partitioning in the microbial community, and therefore suggests a diversified response pattern to future changes in substrate availability and climatic factors. 相似文献
12.
In late March 1997, an open-top-chamber (OTC) CO 2 enrichment study was begun in the Colorado shortgrass steppe. The main objectives of the study were to determine the effect of elevated CO 2 (720 mol mol –1) on plant production, photosynthesis, and water use of this mixed C 3/C 4 plant community, soil nitrogen (N) and carbon (C) cycling and the impact of changes induced by CO 2 on trace gas exchange. From this study, we report here our weekly measurements of CO 2, CH 4, NO x and N 2O fluxes within control (unchambered), ambient CO 2 and elevated CO 2 OTCs. Soil water and temperature were measured at each flux measurement time from early April 1997, year round, through October 2000. Even though both C 3 and C 4 plant biomass increased under elevated CO 2 and soil moisture content was typically higher than under ambient CO 2 conditions, none of the trace gas fluxes were significantly altered by CO 2 enrichment. Over the 43 month period of observation NO x and N 2O flux averaged 4.3 and 1.7 in ambient and 4.1 and 1.7 g N m –2 hr –1 in elevated CO 2 OTCs, respectively. NO x flux was negatively correlated to plant biomass production. Methane oxidation rates averaged –31 and –34 g C m –2 hr –1 and ecosystem respiration averaged 43 and 44 mg C m –2 hr –1 under ambient and elevated CO 2, respectively, over the same time period. 相似文献
13.
This research examines the relationships between El Niño Southern Oscillation (ENSO), water level, precipitation patterns and carbon dioxide (CO 2) exchange rates in the freshwater wetland ecosystems of the Florida Everglades. Data was obtained over a 5-year study period (2009–2013) from two freshwater marsh sites located in Everglades National Park that differ in hydrology. At the short-hydroperiod site (Taylor Slough; TS) and the long-hydroperiod site (Shark River Slough; SRS) fluctuations in precipitation patterns occurred with changes in ENSO phase, suggesting that extreme ENSO phases alter Everglades hydrology which is known to have a substantial influence on ecosystem carbon dynamics. Variations in both ENSO phase and annual net CO 2 exchange rates co-occurred with changes in wet and dry season length and intensity. Combined with site-specific seasonality in CO 2 exchanges rates, El Niño and La Niña phases magnified season intensity and CO 2 exchange rates at both sites. At TS, net CO 2 uptake rates were higher in the dry season, whereas SRS had greater rates of carbon sequestration during the wet season. As La Niña phases were concurrent with drought years and extended dry seasons, TS became a greater sink for CO 2 on an annual basis (−11 to −110 g CO 2 m −2 yr −1) compared to El Niño and neutral years (−5 to −43.5 g CO 2 m −2 yr −1). SRS was a small source for CO 2 annually (1.81 to 80 g CO 2 m −2 yr −1) except in one exceptionally wet year that was associated with an El Niño phase (−16 g CO 2 m −2 yr −1). Considering that future climate predictions suggest a higher frequency and intensity in El Niño and La Niña phases, these results indicate that changes in extreme ENSO phases will significantly alter CO 2 dynamics in the Florida Everglades. 相似文献
14.
We investigated the effects of elevated pCO 2 on cultures of the unicellular N 2-fixing cyanobacterium Crocosphaera watsonii WH8501. Using CO 2-enriched air, cultures grown in batch mode under high light intensity were exposed to initial conditions approximating current atmospheric CO 2 concentrations (∼400 ppm) as well as CO 2 levels corresponding to low- and high-end predictions for the year 2100 (∼750 and 1000 ppm). Following acclimation to CO 2 levels, the concentrations of particulate carbon (PC), particulate nitrogen (PN), and cells were measured over the diurnal cycle for a six-day period spanning exponential and early stationary growth phases. High rates of photosynthesis and respiration resulted in biologically induced pCO 2 fluctuations in all treatments. Despite this observed pCO 2 variability, and consistent with previous experiments conducted under stable pCO 2 conditions, we observed that elevated mean pCO 2 enhanced rates of PC production, PN production, and growth. During exponential growth phase, rates of PC and PN production increased by ∼1.2- and ∼1.5-fold in the mid- and high-CO 2 treatments, respectively, when compared to the low-CO 2 treatment. Elevated pCO 2 also enhanced PC and PN production rates during early stationary growth phase. In all treatments, PC and PN cellular content displayed a strong diurnal rhythm, with particulate C:N molar ratios reaching a high of 22∶1 in the light and a low of 5.5∶1 in the dark. The pCO 2 enhancement of metabolic rates persisted despite pCO 2 variability, suggesting a consistent positive response of Crocosphaera to elevated and fluctuating pCO 2 conditions. 相似文献
15.
Nocturnal CO 2 uptake by a Crassulacean acid metabolism succulent, Agave deserti Engelm. (Agavaceae), was measured so that the resistance properties of the mesophyll chlorenchyma cells and their CO 2 concentrations could be determined. Two equivalents of acidity were produced at night per mole of CO 2 taken up. The nocturnal CO 2 uptake became light-saturated at 3.5 mEinsteins cm −2 of photosynthetically active radiation (400-700 nm) incident during the preceding day; at least 46 Einsteins were required per mole of CO 2 fixed. Variations in the daytime leaf temperature between 20 and 37 C had little effect on nocturnal CO 2 uptake. After the first few hours in the dark, the leaf liquid phase CO 2 resistance (r liqCO2) and the CO 2 concentration in the chlorenchyma cells (c iCO2) both increased, the latter usually reaching the ambient external CO 2 level at the end of the dark period. Increasing the leaf surface temperature above 15 C at night markedly increased the stomatal resistance, r liqCO2, and c iCO2. The minimum rliqCO2 at night was about 1.6 seconds cm−1. Based on the ratio of chlorenchyma surface area to total leaf surface area of 82, this rliqCO2 corresponded to a minimum cellular resistance of approximately 130 seconds cm−1, comparable to values for mesophyll cells of C3 plants. The contribution of the carboxylation reaction and/or other biochemical steps to rliqCO2 may increase appreciably as the nighttime temperature shifts a few degrees from the optimum or after a few hours in the dark, both of which caused large increases in rliqCO2. This necessitates a large internal leaf area for CO2 diffusion into the chlorenchyma to support moderate nocturnal CO2 uptake rates by these succulent leaves. 相似文献
16.
Oxygen respiration rates in pelagic environments are often difficult to quantify as the resolutions of our methods for O 2 concentration determination are marginal for observing significant decreases during bottle incubations of less than 24 hours. Here we present the assessment of a new highly sensitive method, that combine Switchable Trace Oxygen (STOX) sensors and all-glass bottle incubations, where the O 2 concentration was artificially lowered. The detection limit of respiration rate by this method is inversely proportional to the O 2 concentration, down to <2 nmol L −1 h −1 for water with an initial O 2 concentration of 500 nmol L −1. The method was tested in Danish coastal waters and in oceanic hypoxic waters. It proved to give precise measurements also with low oxygen consumption rates (∼7 nmol L −1 h −1), and to significantly decrease the time required for incubations (≤14 hours) compared to traditional methods. This method provides continuous real time measurements, allowing for a number of diverse possibilities, such as modeling the rate of oxygen decrease to obtain kinetic parameters. Our data revealed apparent half-saturation concentrations (K m values) one order of magnitude lower than previously reported for marine bacteria, varying between 66 and 234 nmol L −1 O 2. K m values vary between different microbial planktonic communities, but our data show that it is possible to measure reliable respiration rates at concentrations ∼0.5–1 µmol L −1 O 2 that are comparable to the ones measured at full air saturation. 相似文献
17.
One-year-old plants of the CAM leaf succulent Agave vilmoriniana Berger were grown outdoors at Riverside, California. Potted plants were acclimated to CO 2-enrichment (about 750 microliters per liter) by growth for 2 weeks in an open-top polyethylene chamber. Control plants were grown nearby where the ambient CO 2 concentration was about 370 microliters per liter. When the plants were well watered, CO 2-induced differences in stomatal conductances and CO 2 assimilation rates over the entire 24-hour period were not large. There was a large nocturnal acidification in both CO 2 treatments and insignificant differences in leaf chlorophyll content. Well watered plants maintained water potentials of −0.3 to −0.4 megapascals. When other plants were allowed to dry to water potentials of −1.2 to −1.7 megapascals, stomatal conductances and CO 2 uptake rates were reduced in magnitude, with the biggest difference in Phase IV photosynthesis. The minor nocturnal response to CO 2 by this species is interpreted to indicate saturated, or nearly saturated, phosphoenolpyruvate carboxylase activity at current atmospheric CO 2 concentrations. CO 2-enhanced diurnal activity of ribulose bisphosphate carboxylase activity remains a possibility. 相似文献
18.
Elevated CO 2 can protect plants from heat stress (HS); however, the underlying mechanisms are largely unknown. Here, we used a set of Arabidopsis mutants such as salicylic acid (SA) signaling mutants nonexpressor of pathogenesis-related gene 1 ( npr1-1 and npr1-5) and heat-shock proteins (HSPs) mutants ( hsp21 and hsp70-1) to understand the requirement of SA signaling and HSPs in elevated CO 2-induced HS tolerance. Under ambient CO 2 (380 µmol mol −1) conditions, HS (42°C, 24 h) drastically decreased maximum photochemical efficiency of PSII (Fv/Fm) in all studied plant groups. Enrichment of CO 2 (800 µmol mol −1) with HS remarkably increased the Fv/Fm value in all plant groups except hsp70-1, indicating that NPR1-dependent SA signaling is not involved in the elevated CO 2-induced HS tolerance. These results also suggest an essentiality of HSP70-1, but not HSP21 in elevated CO 2-induced HS mitigation. 相似文献
19.
Elevated CO 2 interactions with other factors affects the plant performance. Regarding the differences between cultivars in response to CO 2 concentrations, identifying the cultivars that better respond to such conditions would maximize their potential benefits. Increasing the ability of plants to benefit more from elevated CO 2 levels alleviates the adverse effects of photoassimilate accumulation on photosynthesis and increases the productivity of plants. Despite its agronomic importance, there is no information about the interactive effects of elevated CO 2 concentration and plant growth regulators (PGRs) on potato ( Solanum tuberosum L.) plants. Hence, the physiological response and source-sink relationship of potato plants ( cvs. Agria and Fontane) to combined application of CO 2 levels (400 vs. 800 µmol mol −1) and plant growth regulators (PGR) [6-benzylaminopurine (BAP) + Abscisic acid (ABA)] were evaluated under a controlled environment. The results revealed a variation between the potato cultivars in response to a combination of PGRs and CO 2 levels. Cultivars were different in leaf chlorophyll content; Agria had higher chlorophyll a, b, and total chlorophyll content by 23, 43, and 23%, respectively, compared with Fontane. The net photosynthetic rate was doubled at the elevated compared with the ambient CO 2. In Agria, the ratio of leaf intercellular to ambient air CO 2 concentrations [C i:C a] was declined in elevated-CO 2-grown plants, which indicated the stomata would become more conservative at higher CO 2 levels. On the other hand, the increased C i:C a in Fontane showed a stomatal acclimation to higher CO 2 concentration. The higher leaf dark respiration of the elevated CO 2-grown and BAP + ABA-treated plants was associated with a higher leaf soluble carbohydrates and starch content. Elevated CO 2 and BAP + ABA shifted the dry matter partitioning to the belowground more than the above-media organs. The lower leaf soluble carbohydrate content and greater tuber yield in Fontane might indicate a more efficient photoassimilate translocation than Agria. The results highlighted positive synergic effects of the combined BAP + ABA and elevated CO 2 on tuber yield and productivity of the potato plants. 相似文献
20.
Chemoautotrophic symbioses, in which endosymbiotic bacteria are the major source of organic carbon for the host, are found in marine habitats where sulfide and oxygen coexist. The purpose of this study was to determine the influence of pH, alternate sulfur sources, and electron acceptors on carbon fixation and to investigate which form(s) of inorganic carbon is taken up and fixed by the gamma-proteobacterial endosymbionts of the protobranch bivalve Solemya velum. Symbiont-enriched suspensions were generated by homogenization of S. velum gills, followed by velocity centrifugation to pellet the symbiont cells. Carbon fixation was measured by incubating the cells with 14C-labeled dissolved inorganic carbon. When oxygen was present, both sulfide and thiosulfate stimulated carbon fixation; however, elevated levels of either sulfide (>0.5 mM) or oxygen (1 mM) were inhibitory. In the absence of oxygen, nitrate did not enhance carbon fixation rates when sulfide was present. Symbionts fixed carbon most rapidly between pH 7.5 and 8.5. Under optimal pH, sulfide, and oxygen conditions, symbiont carbon fixation rates correlated with the concentrations of extracellular CO 2 and not with HCO 3− concentrations. The half-saturation constant for carbon fixation with respect to extracellular dissolved CO 2 was 28 ± 3 μM, and the average maximal velocity was 50.8 ± 7.1 μmol min −1 g of protein −1. The reliance of S. velum symbionts on extracellular CO 2 is consistent with their intracellular lifestyle, since HCO 3− utilization would require protein-mediated transport across the bacteriocyte membrane, perisymbiont vacuole membrane, and symbiont outer and inner membranes. The use of CO 2 may be a general trait shared with many symbioses with an intracellular chemoautotrophic partner. 相似文献
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