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1.
《Process Biochemistry》2010,45(1):81-87
In the present attempt a method for the immobilization of acetylcholine esterase (AChE) was developed. In this method, the enzyme was immobilized onto a ceramic cylinder support using a sol–gel–multiwall carbon nanotube (MWCNT) composite. Response surface methodology (RSM) was used for the design and analysis of immobilization experiments. Quadratic mathematical model equations were derived for the prediction of enzyme activity. Then the effects on enzyme activity at 30, 40 and 50 min after process initiation of varying each of two parameters over five levels were investigated. These parameters were the AChE:MWCNT ratio (X1), and AChE–MWCNT:sol–gel ratio (X2). The optimum values of X1 and X2 for the immobilization of AChE on ceramic packing were found to be 1.07 and 0.43, respectively. Using these optimum parameters it was shown that enzyme immobilization with MWCNTs and sol–gel was more effective than immobilization with sol–gel or graphite and sol–gel. Scanning electron microscopic (SEM) images revealed a porous surface comprised of MWCNT–AChE encapsulated in sol–gel. Furthermore, the system was highly reproducible with standard deviations after three successive assays of 1.88%, 2.11% and 2.13% at 30, 40 and 50 min after process initiation, respectively. 相似文献
2.
Extracellular human granulocyte-macrophage colony stimulating factor (hGM-CSF) expression was studied under the control of
the GAP promoter in recombinant Pichia pastoris in a series of continuous culture runs (dilution rates from 0.025 to 0.2 h−1). The inlet feed concentration was also varied and the steady state biomass concentration increased proportionally demonstrating
efficient substrate utilization and constancy of the biomass yield coefficient (Yx/s) for a given dilution rate. The specific product formation rate (qP) showed a strong correlation with dilution rates demonstrating growth associated product formation of hGM-CSF. The volumetric
product concentration achieved at the highest feed concentration (4×) and a dilution rate of 0.2 h−1 was 82 mg l−1 which was 5-fold higher compared to the continuous culture run with 1× feed concentration at the lowest dilution rate thus
translating to a 40 fold increase in the volumetric productivity. The specific product yield (YP/X) increased slightly from 2 to 2.5 mg g−1, with increasing dilution rates, while it remained fairly invariant, for all feed concentrations demonstrating negligible
product degradation or feed back inhibition. The robust nature of this expression system would make it easily amenable to
scale up for industrial production. 相似文献
3.
Kinetics of 1-hydroxypyrene (1-HP) oxidation catalyzed with recombinant Coprinus cinereus (rCiP) and horseradish (HRP) peroxidases was investigated with a special emphasis for developing a nanomolar hydrogen peroxide
(H2O2) detection system. At pH 8.0 the bimolecular constants of 1-HP oxidation with the ferryl compounds of rCiP and HRP were equal
to (1.0 ± 0.3) × 108 M−1 s−1 and (0.6 ± 0.2) × 108 M−1 s−1, respectively. High bimolecular constants and fluorescence quantum yield of 1-HP (0.66) permitted detection as low as 21
nM of H2O2. To optimize the detection system 1-HP oxidation was modeled at steady-state conditions in the range pH 5.0 to pH 8.0. The
1-HP based detection system was compared with the Amplex Red system. The peroxidase-catalyzed 1-HP oxidation system was used
for determination of ozone in the air. 相似文献
4.
A. König C. Zaborosch A. Muscat K.-D. Vorlop F. Spener 《Applied microbiology and biotechnology》1996,45(6):844-850
Amperometric biosensors for naphthalene were developed using either immobilized Sphingomonas sp. B1 or Pseudomonas fluorescens WW4 cells. The microorganisms were immobilized within a polyurethane-based hydrogel, which was used for a microbial biosensor
for the first time. Both strains were shown to be equally suited for the quantification of naphthalene in aqueous solutions.
The biosensors were tested in a flow-through system and a stirred cell (batch method). In both systems a linear response down
to the detection limit was obtained. Measurements in the flow-through system gave sensitivities of up to 1.2 nA mg−1 l−1 and a linear range from 0.03 mg/l to 2.0 mg/l. The response time (t
95) was 2 min and the sample throughput six per hour; the repeatability was within ±5 %. With the batch method, sensitivities
of between 3 nA mg−1 l−1 and 5 nA mg−1l−1 and a linear range of 0.01–3.0 mg/l were obtained; the response time was between 3 min and 5 min. The sensors reached an
operational lifetime of up to 20 days. The sensitivity of both sensors for naphthalene was, in most cases, more than four
times higher than for various other substrates.
Received: 18 October 1995/Received revision: 22 December 1995/Accepted: 22 January 1996 相似文献
5.
Lakkana Laopaiboon Pornthap Thanonkeo Prasit Jaisil Pattana Laopaiboon 《World journal of microbiology & biotechnology》2007,23(10):1497-1501
Sweet sorghum juice supplemented with 0.5% ammonium sulphate was used as a substrate for ethanol production by Saccharomyces cerevisiae TISTR 5048. In batch fermentation, kinetic parameters for ethanol production depended on initial cell and sugar concentrations.
The optimum initial cell and sugar concentrations in the batch fermentation were 1 × 108 cells ml−1 and 24 °Bx respectively. At these conditions, ethanol concentration produced (P), yield (Y
ps) and productivity (Q
p
) were 100 g l−1, 0.42 g g−1 and 1.67 g l−1 h−1 respectively. In fed-batch fermentation, the optimum substrate feeding strategy for ethanol production at the initial sugar
concentration of 24 °Bx was one-time substrate feeding, where P, Y
ps and Q
p
were 120 g l−1, 0.48 g g−1 and 1.11 g l−1 h−1 respectively. These findings suggest that fed-batch fermentation improves the efficiency of ethanol production in terms of
ethanol concentration and product yield. 相似文献
6.
Jayati Roy Choudhury Lu Rao Ulrich Bierbach 《Journal of biological inorganic chemistry》2011,16(3):373-380
A restriction enzyme cleavage inhibition assay was designed to determine the rates of DNA platination by four non-cross-linking
platinum–acridine agents represented by the formula [Pt(am2)LCl](NO3)2, where am is a diamine nonleaving group and L is an acridine derived from the intercalator 1-[2-(acridin-9-ylamino)ethyl]-1,3-dimethylthiourea
(ACRAMTU). The formation of monofunctional adducts in the target sequence 5′-CGA was studied in a 40-base-pair probe containing
the EcoRI restriction site GAATTC. The time dependence of endonuclease inhibition was quantitatively analyzed by polyacrylamide gel
electrophoresis. The formation of monoadducts is approximately 3 times faster with double-stranded DNA than with simple nucleic
acid fragments. Compound 1 (am2 is ethane-1,2-diamine, L is ACRAMTU) reacts with a first-order rate constant of k
obs = 1.4 ± 0.37 × 10−4 s−1 (t
1/2 = 83 ± 22 min). Replacement of the thiourea group in ACRAMTU with an amidine group (compound 2) accelerates the rate by fourfold (k
obs = 5.7 ± 0.58 × 10−4 s−1, t
1/2 = 21 ± 2 min), and introduction of a propane-1,3-diamine nonleaving group results in a 1.5-fold enhancement in reactivity
(compound 3, k
obs = 2.1 ± 0.40 × 10−4 s−1, t
1/2 = 55 ± 10 min) compared with the prototype. Derivative 4, containing a 4,9-disubstituted acridine threading intercalator, was the least reactive compound in the series (k
obs = 1.1 ± 0.40 × 10−4 s−1, t
1/2 = 104 ± 38 min). The data suggest a correlation may exist between the binding rates and the biological activity of the compounds.
Potential pharmacological advantages of rapid formation of cytotoxic monofunctional adducts over the common purine–purine
cross-links are discussed. 相似文献
7.
To determine the chemical and physicochemical characteristics of dissolved organic carbon in the Ado River and the Yasu River,
the main rivers flowing into Lake Biwa, the adsorption behavior onto hydrous iron oxide (HIO) and the reactivity to KMnO4 oxidant were investigated in parallel with measurement of the distribution profiles of dissolved organic carbon (DOC) along
the rivers. In one year of observation at the mouths of the two rivers, DOC concentrations were found to vary in the Ado over
the range 0.28–1.21 mg C l−1 and in the Yasu over the range 1.01–2.68 mg C l−1. Act-DOC, one of the fractions separated from the total DOC by its adsorption-active character onto HIO at pH 4, was thought
primarily to control the variation of total DOC, as in Lake Biwa. The int-DOC, another fraction separated by its adsorption-inert
or -inactive character onto HIO, remained at almost a steady value around 0.18 ± 0.07 mg C l−1 in the Ado, which was lower than that (0.35 ± 0.05 mg C l−1) in Lake Biwa. The act-DOC in river waters was reactive to KMnO4 oxidant, showing a linear relation with the amount of permanganate consumed for the reaction (chemical oxygen demand: COD).
In river waters, the relation can be approximated by a straight line expressed as COD (mg O2 l−1) = 0.64 × act-DOC (mg C l−1) − 0.02. In contrast, in the lake water the relation was COD (mg O2 l−1) = 0.97 × act-DOC (mg C l−1) − 0.50.
Received: March 3, 1999 / Accepted: December 2, 1999 相似文献
8.
The report is on an electrochemical biosensor with remarkably improved sensitivity toward nitrite. In this strategy, positively
charged gold nanoparticle (PCNA) is used in combination with multiwall carbon nanotubes (MWCNT) by electrostatic adsorption
for fabricating PCNA/MWCNT films. Then hemoglobin (Hb) biocatalyst will easily be attached to the surface of the combination
films aforementioned. After that, the Hb/PCNA films are immobilized onto the Hb/PCNA/MWCNT films through layer-by-layer assembly
technique. The (Hb/PCNA)2/MWNT/GC electrode thus prepared exhibits enhanced electrocatalytic behavior to the reduction of nitrite at −0.10 V versus
SCE in 0.05 M H2SO4 solution. On condition of the low detecting potential and low pH, interference caused by direct electrochemical oxidation or oxidizable
substances can be prevented. Therefore, the modified electrode shows fast response time, very high sensitivity, good selectivity
and stability. The current response of the sensor increases linearly with nitrite concentration from a range of 3.6 × 10−6 to 3.0 × 10−3 M with a detection limit(S /N = 3) of 9.6 × 10−7 M. 相似文献
9.
Decolourization of anaerobically digested and polyaluminium chloride treated distillery spentwash was studied in a fungal
stirred tank aerobic reactor without dilution of wastewater. Aspergillus niger isolate IITB-V8 was used as the fungal inoculum. The main objectives of the study were to optimize the stirrer speed for
achieving maximum decolourization and to determine the kinetic parameters. A mathematical model was developed to describe
the batch culture kinetics. Volumetric oxygen transfer coefficient (k
L
a) was obtained using dynamic method. The maximum specific growth rate and growth yield of fungus were determined using Logistic
equation and using Luedeking–Piret equation. 150 rpm was found to be optimum stirrer speed for overall decolourization of
87%. At the optimum stirrer speed, volumetric oxygen transfer coefficient (k
L
a) was 0.4957 min−1 and the maximum specific growth rate of fungus was 0.224 h−1. The values of yield coefficient (Y
x/s) and maintenance coefficient (m
s) were found to be 0.48 g cells (g substrate)−1 and 0.015 g substrate (g cells)−1 h−1. 相似文献
10.
The growth performance of malolactic fermenting bacteria Oenococcus oeni NCIMB 11648 and Lactobacillus brevis X2 was assessed in continuous culture. O. oeni grew at a dilution rate range of 0.007 to 0.052 h−1 in a mixture of 5:6 (g l−1) of glucose/fructose at an optimal pH of 4.5, and L. brevis X2 grew at 0.010 to 0.089 h−1 in 10 g l−1 glucose at an optimal pH of 5.5 in a simple and safe medium. The cell dry weight, substrate uptake and product formation
were monitored, as well as growth kinetics, yield parameters and fermentation balances were also evaluated under pH control
conditions. A comparison of growth characteristics of two strains was made, and this showed significantly different performance.
O. oeni has lower maximum specific growth rate (μmax=0.073 h−1), lower maximum cell productivity (Q
x
max=17.6 mg cell l−1 h−1), lower maximum biomass yield (Y
x/s
max=7.93 g cell mol−1 sugar) and higher maintenance coefficient (m
s=0.45 mmol−1 sugar g−1 cell h−1) as compared with L. brevis X2 (μmax=0.110 h−1; Q
x
max=93.2 g−1 cell mol−1 glucose; Y
x/s
max=22.3 g cell mol−1 glucose; m
s=0.21 mmol−1 glucose g−1 cell h−1). These data suggest a possible more productive strategy for their combined use in maturation of cider and wine. 相似文献
11.
Zanaty R. Komy Rabei M. Gabar Ahmed A. Shoriet Rehab M. Mohammed 《World journal of microbiology & biotechnology》2006,22(9):975-982
Summary The ability of Pseudomonas
aeruginosa to accumulate Cd(II) ions from wastewater industries was experimentally investigated and mathematically modelled. From the potentiometric titration and non-ideal competitive analysis (NICA) model, it was found that the biomass contains three acidic sites. The values of proton binding (pK
i
=1.66±3.26×10−3, 1.92±1.63×10−4 and 2.16±3.79×10−4) and binding constant of cadmium metal ions (pK
M1=1.99±2.45×10−3 and pK
M2=1.67±4.08×10−3) on the whole surface of biomass showed that protonated functional groups and biosorption of Cd(II) ions could be attributed to a monodentate binding to one acidic site, mainly the carboxylic group. From the isothermal sorption experimental data and Langmuir model, it was also found that the value of Langmuir equilibrium (pK
f) constant is 2.04±2.1×10−5 suggesting that the carboxyl group is the main active binding site. In addition, results showed that the maximum cadmium capacity (q
max) and affinity of biomass towards cadmium metal ions (b) at pH 5.1 and 20 min were 96.5±0.06 mg/g and 3.40×10−3± 2.10×10−3, respectively. Finally, interfering metal ions such as Pb(II), Cu(II), Cr(III), Zn(II), Fe(II), Mn(II), Ca(II) and Mg(II) inhibited Cd(II) uptake. Comparing the biosorption of Cd(II) by various Pseudomonas isolates from contaminated environment samples (soil and sewage treatment plant) showed that maximum capacities and equilibrium times were different, indicating that there was a discrepancy in the chemical composition between biomasses of different strains. 相似文献
12.
Water potential and sap flow rate in adult trees with moist and dry soil as used for the assessment of root system depth 总被引:4,自引:0,他引:4
Sap flow rate (Qw) and leaf water potential (Ψw.leaf) in adult specimens of birch (Betula) and oak (Quercus) were measured under contrasting soil moisture conditions (Ψw.sofl). With sufficient soil moisture Qw reached about 250 cm3h−1 calculated per unit tree-trunk segment as given by 1 cm length of its circumference. In soil water-stress conditions (when
Ψw.leaf = = −15 × 105Pa), birch stopped transpiration and wilted. Oak transpired even when Ψw.leaf fell below −20 × 105Pa. The relation between Qw and Ψw.leaf was always linear and with various Ψw.soil differed in the slopes of regression lines only. Hydraulic conductance (Kwcu) with nonlimiting moisture conditions reached about 6 × 10−9m3 10−5Pa−1s−1 and “conductivity” (“kwa”) when calculated per leaf area unit reached about 23 m 10−5Pa−1s−1. Kwcu and “kwa” were of about one half to nine times greater in birch than in oak. On the basis of relations between Ψw.soil at various depths, Ψw.leaf and Qw (resp. Kw) it is possible to assess the maximal rooting depth and the effective depth where the maximum of absorption of roots occurs.
It is to be seen that the root system macrostructure substantially participates in the drought avoidance of adult trees in
a forest stand. 相似文献
13.
(1) Little information exists on the role of clustered Hox genes in oligodendrocyte (OG) development. This study examines the expression profile of Hoxd1 and identifies a potential
downstream target in the OG lineage. (2) Immunocytochemical analysis of primary mixed glial cultures demonstrated Hoxd1 was
expressed throughout OG development. (3) A human myelin protein gene, myelin oligodendrocyte glycoprotein (MOG), was identified
as a putative downstream target of Hoxd1 through Genbank searches utilizing the Hoxd1 homeodomain consensus binding sequence.
(4) The dissociation coefficient constant (K
D) and dissociation rate constant (k
d) of the Hoxd1–MOG complex, determined using electrophoretic mobility shift assays (EMSAs), were estimated to be 1.9 × 10−7 M and 1.3 × 10−3 s−1, respectively. The DNA–Hoxd1 homeodomain complex had a half-life (t
1/2) of 15 min. (5) Mutational analysis of Hoxd1–MOG complexes revealed the binding affinity of M1 (with mutation from −10545′-TAAT-3′−1051 to TACT within the consensus binding site) and M2 (with mutation from -10545′-TAATTG-3′-1049 to TAATCC within the consensus binding site) probes to the MOG promoter was severely affected. Thus the TAATTG core of the
binding sequence appears important for Hoxd1 specificity. (6) Analysis of the involvement of TAAT sites adjacent to the consensus
sequence in Hoxd1 binding showed the binding affinity of the M3 probe was affected, but not as severely as the M1 and M2 probes.
These in vitro results suggest the TTTAATTGTA sequence is involved in Hoxd1 binding to the MOG promoter but neighboring TAAT
sites may also be needed. Thus, MOG may be a target of Hoxd1. 相似文献
14.
Serge Ostrovidov Patricia Franck Josette Capiaumont Brigitte Dousset Francine Belleville 《In vitro cellular & developmental biology. Animal》1998,34(3):259-264
Summary The effect of low concentrations of hydrogen peroxide (H2O2) (5 × 10−7−9.5 × 10−7
M) on cell growth and antibody production was investigated with murine hybridoma cells (Mark 3 and anti-hPL) in culture. Cell
growth, measured by flow cytometry with morphological parameters, was significantly stimulated by H2O2 (8 × 10−7
M) but H2O2 concentration of 7 × 10−6
M and above increased cell death. H2O2 stimulation of antibody production was nonsignificant. The metabolism of cells treated with 8 × 10−7 or 1 × 10−5
M H2O2 was similar to that of the control in terms of glucose and glutamine consumption, lactate and ammonia production, and amino
acid concentrations in the medium. The concentrations of lactate dehydrogenase, a marker of cell death, in test and control
cells were similar. However, concentrations of intracellular free radicals measured by flow cytometry with dihydrorhodamine
123 (DHR 123) and dichlorofluorescein diacetate (DCFH-DA) as fluorochromes were different. The reactive oxygen species content
of cells in 8 × 10−7
M H2O2 was similar to that of the controls, but there was a sudden, marked production of superoxide anions (detected with DHR 123)
and H2O2 or peroxides (detected with DCFH-DA) by cells incubated with 1 × 10−5
M H2O2 which increased with increasing H2O2 until cell death. 相似文献
15.
The denitrification performance of a lab-scale anoxic rotating biological contactor (RBC) using landfill leachate with high
nitrate concentration was evaluated. Under a carbon to nitrogen ratio (C/N) of 2, the reactor achieved N-NO3
− removal efficiencies above 95% for concentrations up to 100 mg N-NO3
− l−1. The highest observed denitrification rate was 55 mg N-NO3
− l−1 h−1 (15 g N-NO3
− m−2 d−1) at a nitrate concentration of 560 mg N-NO3
− l−1. Although the reactor has revealed a very good performance in terms of denitrification, effluent chemical oxygen demand (COD)
concentrations were still high for direct discharge. The results obtained in a subsequent experiment at constant nitrate concentration
(220 mg N-NO3
− l−1) and lower C/N ratios (1.2 and 1.5) evidenced that the organic matter present in the leachate was non-biodegradable. A phosphorus
concentration of 10 mg P-PO4
3− l−1 promoted autotrophic denitrification, revealing the importance of phosphorus concentration on biological denitrification
processes. 相似文献
16.
Streptomyces lividans 1326 carries inducible mercury resistance genes on the chromosome, which are arranged in two divergently transcribed operons.
Expression of the genes is negatively regulated by the repressor MerR, which binds in the intercistronic region between the
two operons. The merR gene was expressed in E. coli using a T7 RNA polymerase/promoter expression system, and MerR was purified to around 95% homogeneity by ammonium sulfate
precipitation, gel filtration and affinity chromatography. Gel filtration showed that the native MerR is a dimer with a molecular
mass of 31 kDa. Two DNA binding sites were identified in the intercistronic mer promoter region by footprinting experiments. No evidence for cooperativity in the binding of MerR to the adjacent operator
sequences was observed in gel mobility shift assays. The dissociation constants (KD) for binding of MerR were: binding site I, 8.5 × 10−9 M; binding site II, 1.2 × 10−8 M; and for the complete promoter/operator region 1 × 10−8 M. The half-life of the MerR-DNA complex was 19.4 min and 18.8 min for binding site I and binding site II, respectively.
The KD value for binding of mercury(II)chloride to MerR, again determined by mobility shift assay, was 1.1 × 10−7 M.
Received: 18 August 1998 / Accepted: 5 May 1999 相似文献
17.
Toxic at low concentrations, phenol is one of the most common organic pollutants in air and water. In this work, phenol biodegradation
was studied in extreme conditions (80°C, pH = 3.2) in a 2.7 l bioreactor with the thermoacidophilic archaeon Sulfolobus solfataricus 98/2. The strain was first acclimatized to phenol on a mixture of glucose (2000 mg l−1) and phenol (94 mg l−1) at a constant dissolved oxygen concentration of 1.5 mg l−1. After a short lag-phase, only glucose was consumed. Phenol degradation then began while glucose was still present in the
reactor. When glucose was exhausted, phenol was used for respiration and then for biomass build-up. After several batch runs
(phenol < 365 mg l−1), specific growth rate (μX) was 0.034 ± 0.001 h−1, specific phenol degradation rate (qP) was 57.5 ± 2 mg g−1 h−1, biomass yield (YX/P) was 52.2 ± 1.1 g mol−1, and oxygen yield factor
( \textY\textX/\textO 2 ) \left( {{\text{Y}}_{{{\text{X}}/{\text{O}}_{ 2} }} } \right) was 9.2 ± 0.2 g mol−1. A carbon recovery close to 100% suggested that phenol was exclusively transformed into biomass (35%) and CO2 (65%). Molar phenol oxidation constant
( \textY\textO 2 /\textP ) \left( {{\text{Y}}_{{{\text{O}}_{ 2} /{\text{P}}}} } \right) was calculated from stoichiometry of phenol oxidation and introducing experimental biomass and CO2 conversion yields on phenol, leading to values varying between 4.78 and 5.22 mol mol−1. Respiratory quotient was about 0.84 mol mol−1, very close to theoretical value (0.87 mol mol−1). Carbon dioxide production, oxygen demand and redox potential, monitored on-line, were good indicators of growth, substrate
consumption and exhaustion, and can therefore be usefully employed for industrial phenol bioremediation in extreme environments. 相似文献
18.
Bopaiah A. Biddanda Dwight F. Coleman Thomas H. Johengen Steven A. Ruberg Guy A. Meadows Hans W. Van Sumeren Richard R. Rediske Scott T. Kendall 《Ecosystems》2006,9(5):828-842
Dissolution of the Silurian-Devonian aquifer in the Lake Huron Basin has produced several karst formations in the bedrock
(sinkholes), through which groundwater emerges onto the lake floor. During September 2003, we explored a recently discovered
submerged sinkhole ecosystem (55 m × 40 m × ∼1 m) located at a depth of 93 m with a remotely operated vehicle (ROV) equipped
with a conductivity-temperature-depth (CTD) system, an acoustic navigational system, a video camera, and a water sampling
system. In addition to two morphotypes of benthic mats, a 1–2 m thick visibly cloudy near-bottom nepheloid-like layer (sinkhole
plume) with a strong hydrogen sulfide odor prevailed just above the seepage area of clear water. Relative to lake water, water
samples collected within the sinkhole plume were characterized by slightly higher (by 4°C) temperatures, very high levels
of chloride (up to 175 mg l−1) and conductivity (1,700 μS cm−1), as well as extremely high concentrations of sulfate (1,400 mg l−1), phosphorus (3 mg l−1) and particulate organic matter (400 mg C l−1). Compared to background lake water, sinkhole plume water was characterized by approximately twofold lower C:N ratios and
tenfold higher levels of dissolved organic carbon, bacterial biomass as well as heterotrophic bacterial production. Significant
uptake of 14C-bicarbonate in dark incubations provided preliminary evidence for occurrence of chemosynthesis, possibly mediated by specialized
Bacteria and Archea present in this submerged sinkhole ecosystem in the Laurentian Great Lakes. 相似文献
19.
Barrera-Cortés J Manilla-Pérez E Poggi-Varaldo HM 《Bioprocess and biosystems engineering》2006,29(5-6):391-398
The objective of this work was to determine (1) the effect of rotational speed (N) and lifters on the oxygen transfer coefficient (k
L) of a mineral solution and (2) the effect of solids concentration of a slurry soil-mineral solution on k
L, at a fixed value N (0.25 s−1); in both cases the treatment was carried out in an aerated rotating drum reactor (RDR) operated at atmospheric pressure. First, the k
L for the mineral solution was in the range 6.38 × 10−4–7.69 × 10−4 m s−1, which was of the same order of magnitude as those calculated for closed rotating drums supplied with air flow. In general, k
L of RDR implemented with lifters was superior or equal to that of RDR without lifters. For RDR implemented with lifters, k
L increased with N in the range 6.65 × 10−4–10.51 × 10−4 m s−1, whereas k
L of RDR without lifters first increased with N up to N = 0.102 s−1, and decreased beyond this point. Second, regarding soil slurry experiments, an abrupt fall of k
L (ca. 50%) at low values of the solid concentration (C
v) and an asymptotic pattern at high C
v were observed at N = 0.25 s−1. These results suggest that mass transfer phenomena were commanded by the slurry properties and a semi-empirical equation of the form Sh = f(Re, Sc) seems to corroborate this finding. 相似文献
20.
Ecosystem-level experiments on the effects of atmospheric CO2 enrichment and N deposition on forest trees are urgently needed. Here we present data for nine model ecosystems of spruce
(Picea abies) on natural nutrient-poor montane forest soil (0.7 m2 of ground and 350 kg weight). Each system was composed of six 7-year-old (at harvest) trees each representing a different
genotype, and a herbaceous understory layer (three species). The model ecosystems were exposed to three different CO2 concentrations (280, 420, 560 μl l−1) and three different rates of wet N deposition (0, 30, 90 kg ha−1 year−1) in a simulated annual course of Swiss montane climate for 3 years. The total ecosystem biomass was not affected by CO2 concentration, but increased with increasing N deposition. However, biomass allocation to roots increased with increasing
CO2 leading to significantly lower leaf mass ratios (LMRs) and leaf area ratios (LARs) in trees grown at elevated CO2. In contrast to CO2 enrichment, N deposition increased biomass allocation to the aboveground plant parts, and thus LMR and LAR were higher with
increasing N deposition. We observed no CO2 × N interactions on growth, biomass production, or allocation, and there were also no genotype × treatment interactions.
The final leaf area index (LAI) of the spruce canopies was 19% smaller at 420 and 27% smaller at 560 than that measured at
280 μl CO2 l−1, but was not significantly altered by increasing N deposition. Lower LAIs at elevated CO2 largely resulted from shorter branches (less needles per individual tree) and partially from increased needle litterfall.
Independently of N deposition, total aboveground N content in the spruce communities declined with increasing CO2 (−18% at 420 and −31% at 560 compared to 280 μl CO2 l−1). N deposition had the opposite effect on total above ground N content (+18% at 30 and +52% at 90 compared to 0 kg N ha−1 year−1). Our results suggest that under competitive conditions on natural forest soil, atmospheric CO2 enrichment may not lead to higher ecosystem biomass production, but N deposition is likely to do so. The reduction in LAI
under elevated CO2 suggests allometric down-regulation of photosynthetic carbon uptake at the canopy level. The strong decline in the tree nitrogen
mass per unit ground area in response to elevated CO2 may indicate CO2-induced reductions of soil N availability.
Received: 11 May 1997 / Accepted: 4 August 1997 相似文献