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1.
Summary The fluorescent intercalation complex of ethidium bromide (ETB) with DNA was used as a probe to compare the effects of various radicals with respect to impairment of the DNA base-pair region.OH radicals inhibit up to 0.7 dye intercalations perOH at low salt concentration, and for various oxidizing species the effect decreases in the orderOH > Br 2 > N 3 > $$ " align="middle" border="0"> (SCN) 2 . DNA impairment by theOH product of Met-Gly is comparable to that of N 3 , but no effect was found due to the interaction between DNA and Lys-Tyr-Lys phenoxyl radicals. The reducing speciese aq , H, O 2 , and CO 2 hardly affect the DNA-ETB intercalation.  相似文献   

2.
A simple linear relationship between the J coupling constant and the linewidth (1/2) of in-phase NMR peaks has been identified. This relationship permits the rapid and accurate determination of polypeptide J coupling constants from a simple inspection of amide cross peaks in homonuclear 1H TOCSY or 1H NOESY spectra. By using the appropriate set of processing parameters we show that J = 0.5(1/2) – MW/5000 + 1.8 for TOCSY spectra and J = 0.6(1/2) – MW/5000 – 0.9 for NOESY spectra, where 1/2 is the half-height linewidth in Hz and MW is the molecular weight of the protein in Da. The simplicity of this relationship, combined with the ease with which 1/2 measurements can be made, means that J coupling constants can now be rapidly determined (up to 100 measurements in less than 30 min) without the need for any complex curve-fitting algorithms. Tests on 11 different polypeptides involving more than 650 separate J measurements have shown that this method yields coupling constants with an rmsd error (relative to X-ray data) of less than 0.9 Hz. Furthermore, the correlation coefficient between the predicted NMR coupling constants and those derived from high-resolution X-ray crystal structures is typically better than 0.89. These simple linear relationships have been found to be valid for peptides as small as 1 kDa to proteins as large as 20 kDa. Despite the method's simplicity, these results are comparable to the accuracy and precision of the best techniques published to date.  相似文献   

3.
Structures of the Asn linked oligosaccharides of quail egg-yolk immunoglobulin (IgY) were determined in this study. Asn linked oligosaccharides were cleaved from IgY by hydrazinolysis and labelled withp-aminobenzoic acid ethyl ester (ABEE) afterN-acetylation. The ABEE labelled oligosaccharides were then fractionated by a combination of Concanavalin A-agarose column chromatography and anion exchange, normal phase and reversed phase HPLC before their structures were determined by sequential exoglycosidase digestion, methylation analysis, HPLC, and 500 MHz1H-NMR spectroscopy. Quail IgY contained only neutral oligosaccharides of the following categories: the glucosylated oligomannose type (0.6%, Glc1-3Glc1-3Man9GlcNAc2; 35.6%, Glc1-3Man7–9GlcNAc2). oligomannose type (15.0%, with the structure Man5–9GlcNAc2) and biantennary complex type with core structures of-Man1-3(-Man1-6)Man1-4GlcNAc1-4GlcNAc (9.9%),-Man1-3(GlcNAc1-4)(-Man1-6)Man1-4GlcNAc1-4GlcNAc (25.1%) and-Man1-3(GlcNAc1-4)(-Man1-6)Man1-4GlcNAc1-4(Fuc1-6)GlcNAc (11.4%). Although never found in mammalian proteins, glucosylated oligosaccharides (Glc1Man7–9GlcNAc2) have been located previously in hen IgY.Abbreviations IgG, IgM, IgA, IgY immunoglobulin G, M, A and Y, respectively - ABEE p-aminobenzoic acid ethyl ester  相似文献   

4.
Summary In animals with fur or feather coats, heat gain from solar radiation is a function of coat optical, structural, and insulative characteristics, as well as skin color and the optical properties of individual hairs or feathers. In this analysis, I explore the roles of these factors in determining solar heat gain in two desert rodents (the Harris antelope squirrel,Ammospermophilus harrisi, and the round-tailed ground squirrel,Spermophilus tereticaudus). Both species are characterized by black dorsal skin, though they contrast markedly in their general coat thickness and structure. Results demonstrate that changes in coat structure and hair optics can produce differences of up to 40% in solar heat gain between animals of similar color. This analysis also confirms that the model of Walsberg et al. (1978) accurately predicts radiative heat loads within about 5% in most cases. Simulations using this model indicate that dark skin coloration increases solar heat gain by 5%. However, dark skin significantly reduces ultraviolet transmission to levels about one-sixth of those of the lighter ventral skin.Symbols and abbreviations: (unless noted, all radiation relations refer to total solar radiation) absorptivity of individual hairs - C absorptivity of the coat - backward scattering coefficient [reflectivity] of individual hairs - C reflectivity of coat - S reflectivity of skin - forward scattering coefficient [transmissivity] of individual hairs - C transmissivity of coat - S transmissivity of the skin - transmissivity of the coat and skin - transmissivity of the coat to ultraviolet radiation - S transmissivity of the skin to ultraviolet radiation - [(1 – )22] - h C coat thermal conductance [W/m2-°C] - h E coat surface-to-environment thermal conductance [W/m2-°C] - I probability per unit coat depth that a ray will be intercepted by a hair [m–1] - K volumetric specific heat of air at 20°C [1200 J/m3-°C] - l C coat thickness [m] - l H hair length [m] - d hair diameter [m] - n hair density per unit skin area (m–2] - Q ABS heat load on animal's skin from solar radiation [W/m2] - Q I solar irradiance at coat surface [W/m2] - r E external resistance to convective and radiative heat transfer [s/m] - r C coat thermal resistance [s/m]  相似文献   

5.
Summary A constant temperature hot film anemometer has been used to evaluate mean liquid flow velocity, bubble frequency, turbulence scale and intensity, and the rate of energy dissipation by liquid phase bubble flow.Symbols M mass - L lenght - T time - a gas/liquid interfacial area L2 - a=a/VL specific gas/liquid interfacial area with regard to the volume of the liquid L–1 - d bubble diameter L - d mean bubble diameter L - de dynamic equilibrium (maximum stable) bubble size L - dp primary bubble diameter L - ds Sauter bubble diameter L - E specific energy dissipation rate with regard to the volume of the liquid ML–1T–3 - E VL energy dissipation rate ML2T–3 - E=E/ since =1 g cm–3, E has the same numerical value as E. Therefore, the symbol E is used everywhere in the present paper for E and called energy dissipation rate (S. s–2=Stokes. s–2) L2T–3 - EG or G local relative gas hold up L2T–3 - f() autocorrelation function [Eq. (10)] L2T–3 - f(r) cross correlation function [Eq. (11)] L2T–3 - g acceleration of gravity LT–2 - k constant LT–2 - kL mass transfer coefficient LT–1 - kLa volumetric mass transfer coefficient with regard to the volume of the liquid T–1 - N0 number of crossings of u and T–1 - nB bubble frequency T–1 - r distance between two points 1 and 2 of the cross correlation function L - t time T - u momentaneous liquid velocity LT–1 - mean liquid velocity LT–1 - mean square fluctuation velocity L2T–2 - intensity of turbulence LT–1 - x position coordinate L - V volume of the bubbling layer in the column L3 - VL volume of the bubble free layer in the column L3 - V electrical voltage (in Fig. 2) L3 - v velocity scale [Eq. (6)] LT–1 - Wecrit critical Weber number [Eq. (4)] LT–1 - wSG superficial gas velocity LT–1 - wSL superficial liquid velocity LT–1 - G or EG local relative gas hold up LT–1 - smallest scale [Eq. (6)] L - time delay in the autocorrelation function [Eq. (10)] T - energy dissipation scale [E. (15)] L - f: Taylor's vorticity scale [E. (14)] L - kinematic viscosity of the liquid L2T–1 - density of the liquid ML–3 - surface tension MT–2 - dynamic pressure of the turbulence [Eq. (8)] ML–1T–2 - p primary (at the aerator) - e equilibrium (far from the aerator)  相似文献   

6.
The selfassociation of N6,N9-dimethyladenine and N6-dimethyl-N9-ethyladenine has been studied by means of NMR technique. The thermodynamic quantities have been calculated using an isodesmic NMR model with three NMR parameters (the monomer shift M and two complex shifts 2 and 3).The dependence of the thermodynamic quantities on the NMR parameters is discussed. Special attention is given to the determination of M and its temperature dependence.Calculations with 3=2· 2 and M taken independently of temperature result in an average entropy S =–17.9±1.8 e.u. for N6,N9-dimethyladenine and S =–16.7±1.7 e.u. for N6-dimethyl-N9-ethyladenine and in an average enthalpy H=–7.2±0.6 kcal· mol–1 for both substances investigated.Part of the Ph.D. Theses of W. Schimmack and H. Sapper.Dedicated to Professor Dr. A. Schraub on the occasion of his 65th birthday.  相似文献   

7.
By means of reaction calorimetry we measured the apparent enthalpy change, Happ, of the binding of Mn2+-ions to goat -lactalbumin as a function of temperature. The observed Happ can be written as the sum of contributions resulting from a conformational and a binding process. In combination with the thermal unfolding curve of goat -lactalbumin, we succeeded in separating the complete set of thermodynamic parameters (H, G, S, Cp) into the binding and conformational contributions. By circular dichroism we showed that NH 4 + -ions, upon binding to bovine a-lactalbumin, induce the same conformational change as do Na+ and K+: the binding constant equals 98 ± 9 M–1.Abbreviations BLA bovine -lactalbumin - GLA goat -lactalbumin - HLA human -lactalbumin - CD circular dichroism Offprint requests to: H. Van DaelDeceased  相似文献   

8.
The new substrates 4-thiouridine and 4-thiothymidine were proposed for spectrophotometric measurement of the activity of uridine (UP) and thymidine (TP) phosphorylases. At pH 7.5, 4-thiouridine has an absorbance maximum at 330 nm, and the difference in extinction coefficient () between 4-thiouridine and 4-thiouracil is 3000 –1cm–1. 4-Thiouridine proved to be a good substrate for UP: the Michaelis ( ) and catalytic (k cat) constants were estimated respectively at 130 M and 49 s–1 at 25°C. Even a greater (5000 M–1cm–1 at 336 nm) was observed for the 4-thiothymidine/4-thiothymine pair.  相似文献   

9.
Respiratory chain phosphorylation has been investigated in the methylotrophic bacterium Methylophilus methylotrophus following the addition of oxidisable substrates to aerobic, whole cell suspensions. Initial-rate experiments showed that ATP synthesis occurred at the overall expense of AMP and inorganic phosphate via the sequential action of the ATP phosphohydrolase and adenylate kinase; some of the nascent ATP was rapidly used to synthesis nonadenine nucleoside triphosphates. After being corrected for ATP turnover, Pi/O quotients of 0.46 to 0.54, 0.77 and 1.37 nmol/ng-atom O were obtained for the oxidation of methanol dehydrogenase-linked substrates (methanol, ethanol and acetaldehyde), duroquinol and formate (NAD+-linked) respectively. These values were proportional to the H+/O and/or K+/O quotients exhibited by these substrates, and yielded an average H+/ATP (H+/Pi) quotient of 4.2 ng-ion H+/nmol. Steady-state experiments showed that the extent of cellular energisation varied with the respiration rate but was always in the order methanol > duroquinol > acetaldehyde, thus indicating that under these longer-term conditions methanol was completely oxidised to yield PQQH2 and 2NAD(P)H. These results are discussed in terms of the various reactions which lead to the generation or utilisation of the protonmotive force in this organism.Abbreviations FCCP carbonylcyanide p-trifluoromethyxyphenyl-hydrazone - bulk phase, transmembrane electrochemical potential difference of protons ( ) - pH bulk phase, transmembrane pH difference (pHin–pHout) - bulk phase, transmembrane electrical potential difference (in - out) - [P] concentration of anhydride phosphate bonds in adenine nucleotides (2[ATP]+[ADP]) - FPLC fast protein liquid chromatography - PQQ pyrroloquinoline quinone - Gp phosphorylation potential  相似文献   

10.
Recently, we have developed an analytical, semi-microscopic theory for the macroscopic behavior of a solvent-containing black lipid film subjected to an electric cross film voltage, . Here we employ the theoretical expressions derived for the disjoining pressure, D, the film elasticity, F, and the film tension, F, to construct the stability diagram of the film, in the D-. Depending on its state (D, ), the film is stable or is prone to squeezing or bending deformations. For a monooleate film we show how the destruction of the plane film due to a periodic thickness fluctuation (squeezing) is facilitated by two mechanisms: i) lowering of D at fixed ; ii) lowering of at fixed D, provided that the film is in a stable state characterized by D<–7.03×103 dyne/cm2 and >0 mV. Bending of a low tension film (single interface tension s 0.025 dyne/cm1) can be achieved only for >170 mV and D > –8.7 × 104 dyne/cm2. Finally, we demonstrate the existence of a marginal state ( D 0 , 0) where the film is predicted to exhibit strong fluctuations both in the squeezing and in the bending mode.  相似文献   

11.
The relative contribution of autotrophic carbon sources (aquatic macrophytes, flooded forest, phytoplankton) for heterotrophic bacterioplankton was evaluated in a floodplain lake of the Central Amazon. Stable carbon isotopes (13C) were used as tracers. Values of 13C of different autotrophic sources were compared to those of dissolved organic carbon (DOC) and those of bacterially produced CO2.The percentage of carbon derived from C4 macrophytes for bacterially produced CO2 was the highest, on average 89%. The average 13C value of CO2 from bacterial respiration was –18.5 ± 3.3. Considering a fractionation of CO2 of 3 by bacterial respiration, 13C value was –15.5, near C4 macrophyte 13C value (–13.1).The average value of total DOC 13C was –26.8 ± 2.4. The percentage of C4 macrophytes carbon for total DOC was on average 17%. Considering that bacteria consume mainly carbon from macrophytes, the dominance of C3 plants for total DOC probably reflects a faster consumption of the former source, rather than a major contribution of the latter source.Heterotrophic bacterioplankton in the floodplain may be an important link in the aquatic food web, transferring the carbon from C4 macrophytes to the consumers.  相似文献   

12.
J. Sybenga 《Genetica》1965,36(1):243-252
Whilst reliable estimates of chiasma frequencies can usually not be obtained, the probability (b) of a chromosome arm to be bound by at least one chiasma can often be determined. In the absence of interference this probability equals (1–e –2), where 2 is the average chiasma frequency of the chromosome arm and the average crossover frequency or map length. In the presence of interference is shown to retain its genetic meaning as an additive metric that may describe the chromosome arm or other distinctive chromosome segment in terms of genetic recombination. It is a form of potential map length, comparable to, but numerically different from the regular map length. It is termed provisionally crossing-over potential.A chromosome with armsm andn with crossing-over potentials and will form ring bivalents with a frequency (1–e –2).(1–e –2); open bivalents with a frequency (1–e –2).e –2+(1–e –2).e –2; univalent pairs with a frequencye –2.e –2. Estimates of these frequencies yield equations from which and may be solved. In rye (Secale cereale) their ratio (q) is approximately two and differs from the mitotic arm length ratio of 1.4, indicating localization of chiasmata in the long arms.Graphs are given to show how, with constantq, the relation between the probabilitiesb m andb n of the two arms being bound changes with changing averageb.Data are presented on chiasma frequencies in M I, and compared with the frequencies expected in the absence of interference to give an impression of the degree of interference. Apparent fusion of chiasmata simulates interference.  相似文献   

13.
Stable isotopes (13C, D) and radiocarbon weremeasured in methane bubbles emitted from rice paddies and swamps in southernThailand. Methane emitted from the Thai rice paddies was enriched in13C (mean 13C; –51.5 ±7.1 and–56.5 ± 4.6 for mineral soil and peat soil paddies,respectively)relative to the reported mean value of methane from temperate rice paddies(– 63 ± 5). Large seasonal variation was observed in13C(32) in the rice paddies, whereas variationinD was much more smaller (20), indicating that variation in13C is due mainly to changes in methane production pathways.Values of 13C were lower in swamps (–66.1 ±5.1)than in rice paddies. The calculated contribution of acetate fermentation from13C value was greater in rice paddies (mineral soils:62–81%, peat soils: 57–73%) than in swamps (27–42%). Din methane from Thai rice paddies (–324± 7 (n=46)) isrelativelyhigher than those from 14 stations in Japanese rice paddies ranging from–362 ± 5 (Mito: n=2) to –322 ± 8(Okinawa: n=3), due tohigher D in floodwaters. 14C content in methane produced fromThai rice paddies (127±1 pMC) show higher 14Cactivity compared with previous work in paddy fields and those from Thai swamps(110±2 pMC).  相似文献   

14.
The present investigation examined the relationship between CO2 sensitivity [at rest (S R) and during exercise (S E)] and the ventilatory response to exercise in ten elderly (61–79 years) and ten younger (17–26 years) subjects. The gradient of the relationship between minute ventilation and CO2 production ( E/ CO2) of the elderly subjects was greater than that of the younger subjects [mean (SEM); 32.8 (1.6) vs 27.3 (0.4); P<0.01]. At rest, S R was lower for the elderly than for the younger group [10.77 (1.72) vs 16.95 (2.13) 1 · min–1 · kPa–1; 1.44 (0.23) vs 2.26 (0.28) 1 · min–1 · mmHg–1; P<0.05], but S E was not significantly different between the two groups [17.85 (2.49) vs 19.17 (1.62) l · min–1 · kPa–1; 2.38 (0.33) vs 2.56 (0.21) 1 · min–1 · mmHg–1]. There were significant correlations between both S R and S E, and E/ CO2 (P<0.05; P<0.001) for the younger group, bot none for the elderly. The absence of a correlation for the elderly supports the suggestion that E/ CO2 is not an appropriate index of the ventilatory response to exercise for elderly humans.  相似文献   

15.
In this paper we use a dynamical systems approach to prove the existence of a unique critical value c * of the speed c for which the degenerate density-dependent diffusion equation u ct = [D(u)u x ] x + g(u) has: 1. no travelling wave solutions for 0 < c < c *, 2. a travelling wave solution u(x, t) = (x - c * t) of sharp type satisfying (– ) = 1, () = 0 *; '(*–) = – c */D'(0), '(*+) = 0 and 3. a continuum of travelling wave solutions of monotone decreasing front type for each c > c *. These fronts satisfy the boundary conditions (– ) = 1, '(– ) = (+ ) = '(+ ) = 0. We illustrate our analytical results with some numerical solutions.  相似文献   

16.
FT-IR spectroscopy has been used to evaluate the acyl chain conformational ordering of DMPC, DMPE, DMPA (pH 6 and 12), DMPG (pH 1 and 7), and DPPC, DPPE, DPPA (pH 6). The frequencies of the symmetric and antisymmetric methylene stretching vibrations were determined as a function of temperature. In the liquid-crystalline phase the frequencies show a qualitative dependence on the amount of chain disorder. Quantitative data for trans-gauche isomerization were obtained from the integral intensities of the conformation sensitive methylene wagging absorptions at ca. 1368 cm–1 (gtg and gtg sequences), 1356 cm –1 (double gauche) and 1342 cm–1 (end gauche). The integral band intensities were converted to the number of gauche conformers per acyl chain using the calibration factors published by Senak et al. (1991). At 69°C the highest number of gauche conformers excluding contributions from single gauche conformers and jogs (gtttg) are found for PCs (DMPC: 2.6; DPPC: 2.4), followed by DMPG (2.0), phosphatidylethanolamines (DMPE: 1.4; DPPE: 2.0), protonated DMPG (1.5), and phosphatidic acids (DPPA: 1.7; DMPA: 1.4, DMPA2–: 1.7). From 2H-NMR measurements of perdeuterated samples of DMPC, DMPA, DPPC, and DPPA the quadrupolar splittings Qi and the order parameter S CDi of the CD2-segments close to the chain ends could be determined whereas splittings in the plateau region of the chains could not be resolved. The quadrupolar splittings are affected by trans-gauche isomerization, long axis rotation, and restricted wobbling motions of the acyl chains. In the simplest assumption, the order parameter SCD can be expressed as a product of a segmental order parameter S and a lhain order parameter S . For comparison of the different lipids we used average order parameters SCD, obtained by averaging over all values, and S determined from the total number of gauche conformers per chain by FT-IR-spectroscopy, to calculate an empirical average chain order parameter S. The combination of 2H-NMR and FT-IR results allows the estimation of the relative extent of chain wobbling for the different lipid molecules. S is lowest for PCs (S 0.475) while PEs (S 0.51) and PAs (S0.52) show less chain wobbling.Abbreviations FT-IR Fourier transform infrared - 2H-NMR deuterium nuclear magnetic resonance - DMPC(–d54) (perdeuterated) dimyristoyl-phosphatidylcholine - DMPE(–d54) (perdeuterated) dimyristoyl-phosphatidylethanolamine - DMPA(–d54) (perdeuterated) dimyristoyl-phosphatidic acid - DMPG dimyristoyl-phosphatidylglycerol - DPPC(–d62) (perdeuterated) dipalmitoyl-phosphatidylcholine - DPPE(–d62) (perdeuterated) dipalmitoyl-phosphatidylethanolamine - DPPA(–d62) (perdeuterated) dipalmitoyl-phosphatidic acid - gtg gauche ±-trans-gauche± - gtg gauche±-trans-gauche± - dg double gauche - eg end gauche Correspondence to: A. Blume  相似文献   

17.
Ni  Zhang-Lin  Wang  Da-Fu  Wei  Jia-Mian 《Photosynthetica》2002,40(4):517-522
The conserved residue Thr42 of -subunit of the chloroplast ATP synthase of maize (Zea mays L.) was substituted with Cys, Arg, and Ile, respectively, through site-directed mutagenesis. The over-expressed and refolded -proteins were purified by chromatography on DEAE-cellulose and FPLC on mono-Q column, which were as biologically active (inhibiting Ca2+-ATPase activity and blocking proton gate) as the native subunit isolated from chloroplasts. The T42C and T42R showed higher inhibitory activities on the soluble CF1(–) Ca2+-ATPase than the WT. The T42I inhibited the Ca2+-ATPase activity of soluble CF1 and restored photophosphorylation activity of membrane-bound CF1 deficient in the most efficiently. Far-ultraviolet CD spectra showed that the portions of -helix and -sheet structures of the three mutants were somewhat different from WT. Thus the conserved residue Thr42 may be important for maintaining the structure and function of the -subunit and the basic functions of the -subunit as far as an inhibitor of Ca2+-ATPase and the proton gate are related.  相似文献   

18.
Summary The photographic and electrical conductivity methods to measure the structure of two phase flow, especially bubble size, bubble frequency, local gas hold-up and, for the latter, the bubble velocity are described.Symbols specific interfacial area - a gas/liquid interfacial area - B constant in Eq. (4) - d diameter of the bubbles - d mean diameter of the bubbles - dS Sauter diameter - EG relative gas hold up - I current - kL mass transfer coefficient across the gas/liquid interface - kL local kL - LT–1 - LT–1 - 1 longitudinal distance between the start and stop sensors - 1B pierced length of the bubble - t time - t1 length of the square-wave signal at the start sensor - t2 length of the square-wave signal at the stop sensor - t12 time delay between start and stop signals - V volume of the bubbling layer - VL volume of the bubble free layer - VB bubble volume - vB bubble velocity  相似文献   

19.
Structural study of fucoidan from Cladosiphon okamuranus tokida   总被引:1,自引:0,他引:1  
A structural study was carried out on a fucoidan isolated from the brown seaweed Cladosiphon okamuranus. The polysaccharide contained fucose, glucuronic acid and sulfate in a molar ratio of about 6.1 : 1.0 : 2.9. The results of Smith degradation showed that this polysaccharide has a linear backbone of 13-linked -fucopyranose with a half sulfate substitution at the 4-positions, and a portion of the fucose residues was O-acetylated. The data obtained from partial acid hydrolysis, a methylation analysis and NMR spectra indicated that the -glucuronic acid residue is linked to the 2-positions of the fucose residues, which were not substituted by a sulfate group. These results indicated that the average structure of this fucoidan is as follows: -[(3Fuc-4(±OSO3-)1–)53[GlcA12]Fuc1–]n–. (Half of each fucose residue was sulfated. One O-acetyl ester was present in every 6 fucose residues.)  相似文献   

20.
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   

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