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1.
Elevated CO2 and temperature effects on soil carbon and nitrogen cycling in ryegrass/white clover turves of an Endoaquept soil 总被引:11,自引:0,他引:11
Effects of elevated CO2 (700 L L–1) and a control (350 L L–1 CO2) on the productivity of a 3-year-old ryegrass/white clover pasture, and on soil biochemical properties, were investigated with turves of a Typic Endoaquept soil in growth chambers. Temperature treatments corresponding to average winter, spring, and summer conditions in the field were applied consecutively to all of the turves. An additional treatment, at 700 L L–1 CO2 and a temperature 6°C higher throughout than in the other treatments, was included.Under the same temperature conditions, overall herbage yields in the 700 L L–1 CO2 treatment were ca. 7% greater than in the control at the end of the summer period. Root mass (to ca 25 cm depth) in the 700 L L–1 CO2 treatment was then about 50% greater than in the control, but in the 700 L L–1 CO2+6°C treatment it was 6% lower than in the control. Based on decomposition results, herbage from the 700 L L–1+6°C treatment probably contained the highest proportion of readily decomposable components.Elevated CO2 had no consistent effect on soil total C and N, microbial C and N, or extractable C concentrations in any of the treatments. Under the same temperature conditions, it did, however, enhance soil respiration (CO2-C production) and invertase activity. The effects of elevated CO2 on rates of net N mineralization were less distinct, and the apparent availability of N for the sward was not affected. Under elevated CO2, soil in the higher-temperature treatment had a higher microbial C:N ratio; it also had a greater potential to degrade plant materials.Data interpretation was complicated by soil spatial variability and the moderately high background levels of organic matter and biochemical properties that are typical of New Zealand pasture soils. More rapid cycling of C under CO2 enrichment is, nevertheless, indicated. Futher long-term experiments are required to determine the overall effect of elevated CO2 on the soil C balance. 相似文献
2.
The influence of different foliar applications of the triacontanol (Tria.) based plant grow regulator-Miraculan, on growth, CO2 exchange and essential oil accumulation in Lemongrass (Cymbopogon flexuosus L.) Steud. Watts. was studied in glass-house conditions. The yield components, viz., plant height, tillers per plant, biomass yield, accumulation of essential oil, net CO2 exchange and transpiration rates increased with Miraculan treatment of 0.4 g/ml compared to the untreated control, but the number of leaves per tiller remained unaffected. Application of Miraculan at 0.4 g/ml increased micronutrient uptake, total chlorophyll and citral content but decreased chlorophyll a/b ratio and stomatal resistance. Increase in shoot biomass, photosynthesis and chlorophyll were significantly correlated with essential oil content. 相似文献
3.
E. C. Roumen 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1994,89(4):498-503
The inheritance of host plant resistance and its effect on the relative infection efficiency for leaf blast was studied in the crosses IR36/CO39 (partially resistant × highly susceptible) and IR36/IR64 (both partially resistant). On the natural scale, gene action appeared multiplicative. After log transformation, additive effects described most of the genetic variation in the cross IR36/CO39, while additive and dominance effects were about equal in magnitude in the cross IR36/IR64. Dominance was towards increased resistance. No transgressive segregation occurred in the cross IR36/CO39. The number of genes that reduce lesion number was estimated to be zero in CO39 and five or more in IR36. The cross IR36/IR64 showed transgressive segregation in both directions, and IR36 and IR64 each contain at least one gene that is not present in the other cultivar. The heritabilities (narrow sense) in the F2 were low (range 0.06–0.16), while narrow sense heritabilities based on F3 lines were much higher (range 0.41–0.68). Lesion numbers in F3 lines were reasonably correlated with those in F5 progenies derived from the same F2 plant (r was±0.6 in both crosses). Partial resistance can be effectively improved by selecting the most resistant plants from the most resistant F3 lines. 相似文献
4.
Elevated CO2 (ambient + 35 Pa) increased shoot dry mass production in Avena fatua by 68% at maturity. This increase in shoot biomass was paralleled by an 81% increase in average net CO2 uptake (A) per unit of leaf area and a 65% increase in average A at the ecosystem level per unit of ground area. Elevated CO2 also increased ecosystem A per unit of biomass. However, the products of total leaf area and light-saturated leaf A divided by the ground surface area over time appeared to lie on a single response curve for both CO2 treatments. The approximate slope of the response suggests that the integrated light saturated capacity for leaf photosynthesis is 10-fold greater than the ecosystem rate. Ecosystem respiration (night) per unit of ground area, which includes soil and plant respiration, ranged from-20 (at day 19) to-18 (at day 40) mol m-2 s-1 for both elevated and ambient CO2
Avena. Ecosystem below-ground respiration at the time of seedling emergence was -10 mol m-2 s-1, while that occuring after shoot removal at the termination of the experiment ranged from -5 to-6 mol m-2 s-1. Hence, no significant differences between elevated and ambient CO2 treatments were found in any respiration measure on a ground area basis, though ecosystem respiration on a shoot biomass basis was clearly reduced by elevated CO2. Significant differences existed between leaf and ecosystem water flux. In general, leaf transpiration (E) decreased over the course of the experiment, possibly in response to leaf aging, while ecosystem rates of evapotranspiration (ET) remained constant, probably because falling leaf rates were offset by an increasing total leaf biomass. Transpiration was lower in plants grown at elevated CO2, though variation was high because of variability in leaf age and ambient light conditions and differences were not significant. In contrast, ecosystem evapotranspiration (ET) was significantly decreased by elevated CO2 on 5 out of 8 measurement dates. Photosynthetic water use efficiencies (A/E at the leaf level, A/ET at the ecosystem level) were increased by elevated CO2. Increases were due to both increased A at leaf and ecosystem level and decreased leaf E and ecosystem ET. 相似文献
5.
We present a comprehensive dataset of hourly, daily, and monthly measurements of carbon isotope measurements of CO2 in canopy air from a temperate deciduous forest with the aim to identify the relevance of short-term variations in the isotopic signature of ecosystem respiration (13CR) and to understand its underlying physiological processes. We show that during daytime low vertical mixing inside the canopy can lead to decoupling of the air in the lower and upper canopy layer resulting in large spatial variation of 13C in CO2 of canopy air. Intercept of Keeling Plots also showed large temporal variation (3.8) over the course of the day demonstrating that intercepts can differ between day and night and suggesting that choosing the right time for sampling is essential to capture the isotopic signature of ecosystem respiration (13CR). 13CR as obtained from night-time measurements showed large variation of up to 2.65 on a day-to-day basis, which was similar to the observed variation of 13CR over the seasonal cycle (3.08). This highlights the importance of short-term physiological processes within ecosystems for the isotopic composition of CO2 in the atmosphere, not reflected by bulk plant and soil organic samples. At daily and monthly time scales, 13CR increased with increasing ratio of vapour pressure deficit to photosynthetically active radiation, measured 4–5 days before. This suggests that ecosystem respiration was isotopically linked to assimilation. Furthermore, assimilates recently fixed in the canopy seem to form a labile carbon pool with a short mean residence time that is respired back to the atmosphere after 4–5 days. 相似文献
6.
Evaluation of the role of State transitions in determining the efficiency of light utilisation for CO2 assimilation in leaves 总被引:2,自引:0,他引:2
Wheat leaves were exposed to light treatments that excite preferentially Photosystem I (PS I) or Photosystem II (PS II) and induce State 1 or State 2, respectively. Simultaneous measurements of CO2 assimilation, chlorophyll fluorescence and absorbance at 820 nm were used to estimate the quantum efficiencies of CO2 assimilation and PS II and PS I photochemistry during State transitions. State transitions were found to be associated with changes in the efficiency with which an absorbed photon is transferred to an open PS II reaction centre, but did not correlate with changes in the quantum efficiencies of PS II photochemistry or CO2 assimilation. Studies of the phosphorylation status of the light harvesting chlorophyll protein complex associated with PS II (LHC II) in wheat leaves and using chlorina mutants of barley which are deficient in this complex demonstrate that the changes in the effective antennae size of Photosystem II occurring during State transitions require LHC II and correlate with the phosphorylation status of LHC II. However, such correlations were not found in maize leaves. It is concluded that State transitions in C3 leaves are associated with phosphorylation-induced modifications of the PS II antennae, but these changes do not serve to optimise the use of light absorbed by the leaf for CO2 assimilation.Abbreviations Fm, Fo, Fv
maximal, minimal and variable fluorescence yields
- Fm, Fv
maximal and variable fluorescence yields in a light adapted state
- LHC II
light harvesting chlorophyll a/b protein complex associated with PS II
- qP
photochemical quenching
- A820
light-induced absorbance change at 820 nm
- PS I, PS II
relative quantum efficiencies of PS I and PS II photochemistry
- CO
2
quantum yield of CO2 assimilation 相似文献
7.
Polesskaya O. G. Dzhibladze T. G. Kashirina E. I. Alekhina N. D. Bukhov N. G. 《Russian Journal of Plant Physiology》2004,51(3):326-332
The rates of photosynthetic 2 assimilation were determined in fully expanded second leaves of 21-day-old wheat (Triticum aestivum L.) seedlings grown on media supplied with nitrate or ammonia and on a nitrogen-free medium (NO3
–- or NH4
+-treatments and N-deficit treatment, respectively). The maximal quantum efficiency of photosynthesis was independent on conditions of nitrogen nutrition. When leaves were exposed to 0.03% 2 and high-intensity light, the lowest photosynthetic rate was noted for N-deficit treatment and the highest rate was characteristic of NH4
+ treatment. The elevation of the 2 concentration in the gas phase to 0.1% stimulated photosynthesis at high-intensity light in all treatments. The rate of 2 uptake by the leaf of N-deficient seedlings increased with 2 concentration to a larger extent than in other treatments and approached the 2 uptake rate characteristic of the NO3
– treatment. In plants grown on a nitrogen-free medium, the leaf accumulated lesser amounts of reduced nitrogen and higher amounts of starch, but the content of chloroplast protein corresponded to that of NO3
– treatment. In the leaf of NH4
+-treated seedlings, the rate of 2 assimilation was higher than in the leaf of NO3
– treated plants, regardless of the composition of the gas mixture. The ammonium-type nutrition, as compared to the nitrate-type nutrition, elevated the amount of reduced nitrogen in the leaf and promoted accumulation of chlorophyll and protein, the chloroplast protein in particular. 相似文献
8.
D. Singh 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1985,70(4):413-416
Summary Thirty-one toria genotypes were compared with three well-established cultivars, Ludhiana Composite-2, K-1 and TCSU-2 (standard testers). The genotypes, which were almost identical to a standard tester in response to environmental variations and which also had other desirable characteristics, were considered to be acceptable for commercial cultivation. Using this criterion, TCSU-7, TH-5 and TH-4 were found to be acceptable for commercial cultivation. TH-4 and TCSU-7 were found superior to TH-5 if r2 can be considered as a measure of the agronomical manipulations expected in environmental variations. 相似文献
9.
Elevated CO2 effects on carbon and nitrogen cycling in grass/clover turves of a Psammaquent soil 总被引:1,自引:0,他引:1
Effects of elevated CO2 (525 and 700 L L–1), and a control (350 L L–1 CO2), on biochemical properties of a Mollic Psammaquent soil in a well-established pasture of C3 and C4 grasses and clover were investigated with continuously moist turves in growth chambers over four consecutive seasonal temperature regimes from spring to winter inclusive. After a further spring period, half of the turves under 350 and 700 L L–1 were subjected to summer drying and were then re-wetted before a further autumn period; the remaining turves were kept continuously moist throughout these additional three consecutive seasons. The continuously moist turves were then pulse-labelled with 14C-CO2 to follow C pathways in the plant/soil system during 35 days.Growth rates of herbage during the first four seasons averaged 4.6 g m–2 day–1 under 700 L L–1 CO2 and were about 10% higher than under the other two treatments. Below-ground net productivity at the end of these seasons averaged 465, 800 and 824 g m–2 in the control, 525 and 700 L L–1 treatments, respectively.in continuously moist soil, elevated CO2 had no overall effects on total, extractable or microbial C and N, or invertase activity, but resulted in increased CO2-C production from soil, and from added herbage during the initial stages of decomposition over 21 days; rates of root decomposition were unaffected. CO2 produced h–1 mg–1 microbial C was about 10% higher in the 700 L L–1 CO2 treatment than in the other two treatments. Elevated CO2 had no clearly defined effects on N availability, or on the net N mineralization of added herbage.In the labelling experiment, relatively more 14C in the plant/soil system occurred below ground under elevated CO2, with enhanced turnover of 14C also being suggested.Drying increased levels of extractable C and organic-N, but decreased mineral-N concentrations; it had no effect on microbial C, but resulted in lowered microbial N in the control only. In soil that had been previously summer-dried, CO2 production was again higher, but net N mineralization was lower, under elevated CO2 than in the control after autumn pasture growth.Over the trial period of 422 days, elevated CO2 generally appears to have had a greater effect on soil C turnover than on soil C pools in this pasture ecosystem. 相似文献
10.
Summary Organic pyrophosphates such as UppA and NAD are formed when a solution containing a nucleotide, a nucleoside 5-polyphosphate, Mg2+ and imidazole are allowed to dry out. We suggest that this synthesis may have occured concurrently with oligonucleotide formation.Abbreviations Im
Imidazole
- CDI
1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride
- EDTA
ethylenediaminetetraacetic acid
- A
adenosine
- U
uridine
- pnA
adenosine 5-poly-phosphate containing n phosphate residues
- pU
uridine 5-phosphate
- AppA
P1,P2-diadenosine 5-pyrophosphate
- UppA
P1-(uridine 5)-P2-(adenosine 5)-pyrophosphate
- ImpA
adenosine 5-phosphorimidazolide
- NMN
nicotinamide mononucleotide
- NAD
nicotinamide-adenine dinucleotide 相似文献
11.
Summary To determine whether sweet potato (Ipomoea batatas (L.) Poir.) takes up organic matter through the roots from the medium, the concentrations of natural14C (14C) in plant organic matter, atmospheric CO2 and compost applied to media were examined under soil and sand culture conditions. In these experiments, three kinds of composts of different 14C were used. CO2 derived from the mineralization of compost was continuously pumped out from the pots and its direct uptake by the leaves was prevented.14C of plant parts harvested after the 43 days experimental period were affected by the 14C of the compost in the treatments where the compost of rice straw was applied, and which suggested that a significant amount of plant carbon was derived from the compost. 相似文献
12.
Photosynthetic carbon fixation of freshly isolated cells of Prochloron, the symbiont of Lissoclinum patella, proceeded at high rates (80–180 mol O2·mgChl-1·h-1) in buffered seawater and showed a typical light response, saturating at about 300 E·m-2·s-1. However, in NaCl solutions osmotically equivalent to seawater CO2-dependent O2 evolution ceased or was severely inhibited. Hypotonic or hypertonic conditions induce degrees of swelling or shrinkage, respectively, apparently causing similar increases in the plasmamembrane's permeability to ferricyanide. Initially high, but rapidly declining, rates of electron transport were observed when the cells were suspended in distilled water. This inhibition was not caused by rupture of the cells, indicating instead diffusive loss of some essential factor(s) which normally exchange easily and rapidly between the cells and/or the host environment. Such rapid exchange may be part of the mechanism of this symbiosis and, if not adequately understood, may frustrate attempts to culture Prochloron away from its host.Abbreviations HEPES
N-2-hydroxyethyl piperazine-N-2 ethane sulphonic acid
- EPPS
N-2-hydroxyethyl propane sulphonic acid
- FeCN
potassium ferricyanide
- DBMIB
2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- TMPD
N,N,N,N,-tetramethyl-p-phenylenediamine
- DCIP
2,6-dichlorophenol-indophenol
- MV
methylviologen
- PS
photosystem
- Chl
chlorophyll
Publication No. 219 of the Australian Institute of Marine Science 相似文献
13.
Micropropagated plantlets are fragile and often lack sufficient vigour to survive the acclimatization shock during transplantation to the soil. Effects of photosynthetic photon flux densities (PPFDs) on growth, photosynthesis and anatomy of micropropagated Doritaenopsis were studied after 4 months of acclimatization in a greenhouse at 25 °C. The plantlets were transferred to three different PPFDs for four months, i.e. low light (175), intermediate light (270) and high light (450 mol m–2 s–1). For most of the growth parameters measured i.e. leaf length, leaf area, leaf width, fresh weight, dry weight, chlorophyll (Chl) a/b ratio, were greater for the intermediate light levels after 4 months of acclimatization. The only exception was leaf thickness, which was increased more under high light levels. Results showed that the survival of Doritaenopsis plantlets was greatest (90%) in low light and intermediate light (89%) compared with only (73%) at high light. However, at low light levels, pigment concentrations (chlorophyll a, b and total chlorophyll) were higher. Net CO2 assimilation (A), stomatal conductance (g) and transpiration (E) were higher in plantlets grown at high level PPFD than at low after 4 months of acclimatization. Photosynthetic efficiency (Fv/Fm) decreased insignificantly; only at mid day for the high light treatment whereas leaf temperature and stomatal closure increased compared to low light. Scanning electron microscopic (SEM) images of leaves from acclimatized plantlets showed an increase in wax formation for the high light grown plantlets compared to those at low light. Microscopic analysis of acclimatized root sections showed highly developed multiseriate-velamen layers and higher root cell activity; while shoots had larger leaf air spaces than those of in vitro grown plantlets. These results suggest that physiological acclimation occurs at the intermediate PPFD (270 mol m–2 s–1) in Doritaenopsis compared to treatment at the high light level. 相似文献
14.
Yasuo Kagawa Shigeo Ohta Mitsuo Harada Hiroshi Kihara Yuji Ito Mamoru Sato 《Journal of bioenergetics and biomembranes》1992,24(5):441-445
The basic structures of the catalytic portion (F1, 33) of ATP synthase are the 33 hexamer (oligomer with cooperativity) and 11 heterodimer (protomer). These were reconstituted from the and subunits of thermophilic F1 (TF1), and the 33 hexamer was crystallized. On electrophoresis, both the dimer and hexamer showed bands with ATPase activity. Using the dimer and hexamer, we studied the nucleotide-dependent rapid molecular dynamics. The formation of the hexamer required neither nucleotide nor Mg. The hexamer was dissociated into the dimer in the presence of MgADP, while the dimer was associated into the hexamer in the presence of MgATP. The hexamer, like mitochondrial F1 and TF1, showed two kinds of ATPase activity: one was cooperative and was inhibited by only one BzADP per hexamer, and the other was inhibited by three BzADP per hexamer. 相似文献
15.
The light dependence of quantum yields of Photosystem II (II) and of CO2 fixation were determined in C3 and C4 plants under atmospheric conditions where photorespiration was minimal. Calculations were made of the apparent quantum yield for CO2 fixation by dividing the measured rate of photosynthesis by the absorbed light [A/I=CO2 and of the true quantum yield by dividing the estimated true rate of photosynthesis by absorbed light [(A+Rl)/Ia=CO2·], where RL is the rate of respiration in the light. The dependence of the II/CO2 and II/CO2
* ratios on light intensity was then evaluated. In both C3 and C4 plants there was little change in the ratio of II/CO2 at light intensities equivalent to 10–100% of full sunlight, whereas there was a dramatic increase in the ratio at lower light intensities. Changes in the ratio of II/CO2 can occur because respiratory losses are not accounted for, due to changes in the partitioning of energy between photosystems or changes in the relationship between PS II activity and CO2 fixation. The apparent decrease in efficiency of utilization of energy derived from PS II for CO2 fixation under low light intensity may be due to respiratory loss of CO2. Using dark respiration as an estimate of RL, the calculated II/CO2
* ratio was nearly constant from full sunlight down to approx 5% of full sunlight, which suggests a strong linkage between the true rate of CO2 fixation and PS II activity under varying light intensity. Measurements of photosynthesis rates and II were made by illuminating upper versus lower leaf surfaces of representative C3 and C4 monocots and dicots. With the monocots, the rate of photosynthesis and the ratio of II/CO2 exhibited a very similar patterns with leaves illuminated from the adaxial versus the abaxial surface, which may be due to uniformity in anatomy and lack of differences in light acclimation between the two surfaces. With dicots, the abaxial surface had both lower rates of photosynthesis and lower II values than the adaxial surface which may be due to differences in anatomy (spongy versus palisade mesophyll cells) and/or light acclimation between the two surfaces. However, in each species the response of II/CO2 to varying light intensity was similar between the two surfaces, indicating a comparable linkage between PS II activity and CO2 fixation.Abbreviations A
measured rate of CO2 assimilation
- A+RL
true rate of CO2 assimilation; e
- CO2
estimate of electrons transported through PSII per CO2 fixed by RuBP carboxylase
- f
fraction of light absorbed by Photosystem II
- F'm
yield of PSII chlorophyll fluorescence due to a saturating flash of white light under steady-state photosynthesis
- Fs
variable yield of fluorescence under steady-state photosynthesis; PPFD-photosynthetic photon flux density
- Ia
absorbed PPFD
- PS II
Photosystem II
- Rd
rate of respiration in the dark
- RI
rate of respiration in the light estimated from measurement of Rd or from analysis of quantum yields
-
apparent quantum yield of CO2 assimilation under a given condition (A/absorbed PPFD)
-
true quantum yield of CO2 assimilation under a given condition [(A+RL)/(absorbed PPFD)]
-
quantum yield for photosynthetic O2 evolution
-
electrons transported via PS II per quantum absorbed by PS II
Supported by USDA Competitive Grant 90-37280-5706. 相似文献
16.
Fumiaki Nakatsubo T. Kent Kirk Mikio Shimada Takayoshi Higuchi 《Archives of microbiology》1981,128(4):416-420
The degradation of the phenylcoumaran substructure model compound methyl dehydrodiconiferyl alcohol by the white-rot wood decay fungus Phanerochaete chrysosporium was investigated using culture conditions optimized for lignin oxidation. Initial attack was in the cinnamyl alcohol side chain, which was oxidized to a glycerol structure. This was subsequently converted by loss of the two terminal carbon atoms, C and C, to yield a C-aldehyde structure, which was further oxidized to the C-acid compound. The next detected intermediate, a phenylcoumarone, was produced by double bond formation between C and C, and oxidation of the C-alcohol to an aldehyde group. Further oxidation of C to an acid yielded the next intermediate. The final identified degradation product was veratric acid. No products from the 5-substituted aromatic ring, and no phenolic products, were found. The initial glycerol-containing intermediate was a mixture of the threo and erythro forms, and no optical activity could be found, suggesting that its formation might have involved nonstereospecific C-C epoxidation followed by non-enzymatic hydrolysis of the epoxide.Abbreviations TLC
thin layer chromatography
- LDA
lithium diisopropyl amide
- DDQ
2,3-dichloro-5,6-dicyanobenzoquinone
- MS
mass spectrometry
- UV
ultraviolet spectroscopy 相似文献
17.
Our investigations of diurnal variations of the 13C/12C ratio and CO2 content in soil air were carried out in three environments during periods of high biosphere activity. It has been observed that diurnal variation of CO2 concentration is negatively correlated 13. Particularly great variations occurred at shallow soil depths (10–30 cm) when the plant cover activity was high while the soil temperature was rather low. Under such conditions the 13 variations had the magnitude of 4, while the CO2 concentration varied more than doubly. The maximum of the 13C/12C ratlo and the minimum of the CO2 concentration in a cultivated field with winter wheat took place in the afternoon, whereas in deciduous forest similar patterns were observed at dawn. In these cases soil temperatures at 10 cm depths varied less than 2°C. Hence, under wheat the variation in root respiration rate seem to be the main reason of the recorded varations. In an uncultivated grass-field during the hottest period in summer we did not measure any distinct variations of CO2 properties in spite of the fact that soil temperature varied up to 5°C. This might be due to dominant microbial respiration at the high soil temperature, which exceeded 20°C. 相似文献
18.
George T. Byrd T. Loboda Clanton C. Black Jr. R. Harold Brown 《Photosynthesis research》1995,44(3):253-260
Onion (Allium cepa L.) plants were examined to determine the photosynthetic role of CO2 that accumulates within their leaf cavities. Leaf cavity CO2 concentrations ranged from 2250 L L–1 near the leaf base to below atmospheric (<350 L L–1) near the leaf tip at midday. There was a daily fluctuation in the leaf cavity CO2 concentrations with minimum values near midday and maximum values at night. Conductance to CO2 from the leaf cavity ranged from 24 to 202 mol m–2 s–1 and was even lower for membranes of bulb scales. The capacity for onion leaves to recycle leaf cavity CO2 was poor, only 0.2 to 2.2% of leaf photosynthesis based either on measured CO2 concentrations and conductance values or as measured directly by 14CO2 labeling experiments. The photosynthetic responses to CO2 and O2 were measured to determine whether onion leaves exhibited a typical C3-type response. A linear increase in CO2 uptake was observed in intact leaves up to 315 L L–1 of external CO2 and, at this external CO2 concentration, uptake was inhibited 35.4±0.9% by 210 mL L–1 O2 compared to 20 mL L–1 O2. Scanning electron micrographs of the leaf cavity wall revealed degenerated tissue covered by a membrane. Onion leaf cavity membranes apparently are highly impermeable to CO2 and greatly restrict the refixation of leaf cavity CO2 by photosynthetic tissue.Abbreviations Ca
external CO2 concentration
- Ci
intercellular CO2 concentration
-
CO2 compensation concentration
- PPFR
photosynthetic photon fluence rate 相似文献
19.
The limited proteolytic pattern of transducin,G
t
, and its purified subunits with chymotrypsin were analyzed and the cleavage sites on the
t
subunit were identified. The
t
subunit in the GTPS bound form was cleaved into a major 38 kD fragment, whereas
t
-GDP was progressively digested into 38, 23, 21, and 15 kD fragments. The
t
subunit was not very sensitive to proteolytic digestion with chymotrypsin. The
t
subunit was not cleaved and only a small portion of
t
was digested into several fragments. In order to determine which proteolytic fragment of
t
still contained the carboxyl terminal region, chymotrypsinization was carried out usingG
t
previously32P-labeled at Cys347 by petrussis toxin-catalyzed ADP-ribosylation. The32P-label was mainly associated with the
t
subunit and a 15 kD fragment. The 23 and 21 kD fragments were not32P-labeled. Analysis of amino terminal sequences of 38, 21, and 15 kD proteolytic bands allowed the identification of the major cleavage sites. Chymotrypsin had two cleavage sites in the amino terminal region of
t
, at Leu15 and Leu19. Chymotrypsin removed 15–19 amino acid residues from the amino terminus of
t
, generating two peptides (38 kD) which comigrates in gel electrophoresis. Chymotrypsin also cleaved at Trp207 in a conformation-dependent manner. Trp207 of
t
-GTPS was resistant to proteolysis but
t
-GDP and the 38 kD fragments of
t
-GDP produced the 23 and 21 kD fragments, respectively, and a 15 kD fragment containing the carboxyl terminus. This proves that the environment of Trp207 changes when GTP or GTPS is bound, leading to its inaccessibility to chymotrypsin. 相似文献
20.
Jacques C. Finlay 《Biogeochemistry》2003,62(3):231-252
Iinvestigated controls of stream dissolved inorganic carbon (DIC) sources andcycling along a stream size and productivity gradient in a temperate forestedwatershed in northern California. Dissolved CO2 (CO2(aq))dynamics in heavily shaded streams contrasted strongly with those of larger,open canopied sites. In streams with canopy cover > 97%, CO2 (aq)was highest during baseflow periods (up to 540 M) and wasnegatively related to discharge. Effects of algal photosynthesis on CO2(aq) were minimal and stream CO2 (aq) was primarily controlledby groundwater CO2 (aq) inputs and degassing losses to theatmosphere. In contrast to the small streams, CO2 (aq) in larger,open-canopied streams was often below atmospheric levels at midday duringbaseflow and was positively related to discharge. Here, stream CO2(aq) was strongly influenced by the balance between autotrophic andheterotrophic processes. Dynamics of HCO3
– werelesscomplex. HCO3
– and Ca2+ were positivelycorrelated, negatively related to discharge, and showed no pattern with streamsize. Stable carbon isotope ratios of DIC (i.e. 13C DIC)increased with stream size and discharge, indicating contrasting sources of DICto streams and rivers. During summer baseflows, 13C DIC were13C-depleted in the smallest streams (minimum of–17.7) due to the influence of CO2 (aq) derived frommicrobialrespiration and HCO3
– derived from carbonateweathering. 13C DIC were higher (up to –6.6)inthe larger streams and rivers due to invasion of atmospheric CO2enhanced by algal CO2 (aq) uptake. While small streams wereinfluenced by groundwater inputs, patterns in CO2 (aq) and evidencefrom stable isotopes demonstrate the strong influence of stream metabolism andCO2 exchange with the atmosphere on stream and river carbon cycles. 相似文献