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1.
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   

2.
Summary The solubility of oxygen in the liquid phase of a bioreactor was changed by a ramp change of temperature, and kLa was determined from the resulting return to equilibrium of dissolved oxygen activity. The maximum kLa that can be measured by this method in a standard laboratory scale bioreactor is 145 h–1 corresponding to a temperature change rate of 320°C h–1.Nomenclature p Difference between pG and pL (% saturation) - T Ramp change of temperature (°C) - E Temperature-compensated output from the oxygen electrode (A) - Eu Uncompensated output from the oxygen electrode (A) - kLa Overall volumetric mass transfer coefficient (h–1) - kLaTm Overall volumetric mass transfer coefficient at temperature Tm (h–1) - PG Dissolved oxygen activity in equilibrium with the gas phase (% saturation) - pL Dissolved oxygen activity (% saturation) - pLm Dissolved oxygen activity at time tm (% saturation) - t Time (h) - tm Time of maximum p (h) - T Temperature (°C) - Tcal Calibration temperature of the oxygen electrode (°C) - Tm Final temperature after a temperature shift (°C) - Tn Temperature at time tn  相似文献   

3.
Summary By applying photographic, electrical conductivity, and electrooptical methods, the transverse variation of bubble size and velocity, the local gas hold up, and the local specific gas/liquid interfacial area were estimated in a bench scale bubble-column bioreactor containing model cultivation media. The liquid velocity profile, the transverse turbulence intensity variations, and the turbulence energy dissipation scale were also measured by a hot film turbulence probe and constant temperature anemometer technique.A significant relationship was found between the two-phase flow fluid dynamical state and the transverse variation of the various properties.Symbols M mass - L length - T time - a gas/liquid interfacial area L2 - specific gas/liquid interfacial area with regard to the bubbling layer volume L–1 - D transverse coordinate (measured from the wall of the column) L - d bubble diameter L - d mean bubble diameter L - de dynamic equilibrium (maximum stable) bubble diameter 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 - EVL energy dissipation rate ML2T–3 - , since =1 g/cm3, E has the same numerical value as E. Therefore, the symbol E is used everywhere in the present paper for E for simplicity and called energy dissipation rate (S.s–2=Stokes.s–2) L2T–3 - EG or local relative gas holdup - f (r) cross correlation function - g acceleration of gravity LT–2 - h longitudinal distance from the aerator L - relative turbulence intensity - NO number of u and crossings T–1 - nB bubble frequency T–1 - r distance between two points 1 and 2 of the cross correlation function L - t time - u instantaneous liquid velocity LT–1 - mean liquid velocity LT–1 - mean square fluctuation velocity L2T–2 - turbulence intensity LT–1 - wSG superficial gas velocity LT–1 - wSL superficial liquid velocity LT–1 - or EG local relative gas holdup LT–1 - energy dissipation scale L - kinematic liquid viscosity L2T–1 - liquid density M L–3 - surface tension M T–2 - dynamic turbulence pressure M L–1T–2 Indices p primary (at the aerator) - e equilibrium (far from the aerator)  相似文献   

4.
The disruption of a typical filamentous fungus, a native strain of Neurospora sitophila, was studied using a glass bead mill of novel design (the Sulzer Annu Mill 01). Cell concentration (in the range of 2.5–5 g dry weight/L) had little influence on the disruption attained. Disruption increased with increasing rotor speed (1000 –4000 r.p.m.) and number of passes (up to six passes) through the Annu Mill. Disruption was observed to follow traditional first-order kinetics for bead mills possessing predominantly plug flow characteristics. It was concluded that in general the Annu Mill would be applicable for the disruption of filamentous organisms.Nomenclature CP aqueous-phase soluble protein concentration of disrupted sample (g/mL) - CP,MAX aqueous-phase soluble protein concentration of a completely disrupted sample (g/mL) - CPO aqueous-phase soluble protein concentration of undisrupted sample (g/mL) - N number of passes though the bead mill (–) - R total fraction of cells disrupted (–) Greek Letters C internal moisture volume fraction of undisrupted cells (–) - L aqueous phase volume fraction of disrupted cell suspension (–) - LO aqueous phase volume fraction of undisrupted cell suspension (–) - L,MAX aqueous phase volume fraction at complete disruption (R=1) (–) - fluid density (kg/m3) - C density of the microorganism (kg/m3) - L density of the suspending aqueous phase (kg/m3) - suspension batch residence time in the Annu Mill 01 (min.) Abbreviations DW dry weight  相似文献   

5.
Summary The following equations represent the influence of the ethanol concentration (E) on the specific growth rate of the yeast cells () and on the specific production rate of ethanol () during the reactor filling phase in fed-batch fermentation of sugar-cane blackstrap molasses: = 0 - k · E and v = v 0 · K/(K +E) Nomenclature E ethanol concentration in the aqueous phase of the fermenting medium (g.L–1) - Em value of E when = 0 or = 0 (g.L–1) - F medium feeding rate (L.h–1) - k empirical constant (L.g–1.h–1) - K empirical constant (g.L–1) - Mas mass of TRS added to the, reactor (g) - Mcs mass of consumed TRS (g) - Me mass of ethanol in the aqueous phase of the fermenting medium (g) - Ms mass of TRS in the aqueous phase of the fermenting medium (g) - Mx mass of yeast cells (dry matter) in the fermenting medium (g) - r correlation coefficient - S TRS concentration in the aqueous phase of the fermenting medium (g.L–1) - Sm TRS concentration of the feeding medium (g.L–1) - t time (h) - T temperature (° C) - TRS total reducing sugars calculated as glucose - V volume of the fermenting medium (L) - V0 volume of the inoculum (L) - X yeast cells concentration (dry matter) in the fermenting medium (g.L–1) - filling-up time (h) - specific growth rate of the yeast cells (h–1) - 0 value of when E=0 - specific production rate of ethanol (h–1) - 0 value of when E=0 - density of the yeast cells (g.L–1) - dry matter content of the yeast cells  相似文献   

6.
Summary The ethanol yield was not affected and the ethanol productivity was increased when exponentially decreasing feeding rates were used instead of constant feeding rates in fed batch ethanol fermentations. The influences of the initial sugar feeding rate on the ethanol productivity, on the constant ethanol production rate during the feeding phase and on the initial ethanol production specific rate are represented by Monod-like equations.Nomenclature F reactor feeding rate (L.h–1) - Fo initial reactor feeding rate (L.h–1) - K time constant; see equation (l) (h–1) - ME mass of ethanol in the fermentor (g) - Ms mass of TRS in the fermentor (g) - Mx mass of yeast cells (dry matter) in the fermentor (g) - P ethanol productivity (g.L–1.h–1) - R ethanol constant production rate during the feeding phase (g.h–1) - s standard deviation - So TRS concentration in the feeding mash (g.L–1) - t time (h) - T fermentor filling-up-time (h) - T time necessary to complete the fermentation (h) - TRS total reducing sugars calculated as glucose (g.L–1) - Vo volume of the inoculum (L) - Vf final volume of medium in the fermentor (L) - Xo yeast concentration of the inoculum (dry matter) (g.L–1) - ethanol yield (% of the theoretical value) - initial specific rate of ethanol production (h–1)  相似文献   

7.
Summary The kinetics of acetate biomethanation was studied in a high recycle ratio biological fluidized bed reactor behaving in practice as a completely mixed reactor. The active biofilm consisted of bacteria from a methane fermenter that after spontaneous immobilization on the bed particles (sand) were adapted to acetate as the only carbon source. The effects of temperature (13°, 20°, 25° and 35°C), substrate concentration (500, 1000 and 1500 mg chemical oxygen demand (COD) l-1) and hydraulic retention time (1 to 8 h) on substrate consumption were studied. Maximum substrate consumption (as % COD reduction) amounted from 25% (13°C, 1500 mg COD l-1) to 93% (35°C, 500 mg COD l-1). At 35°C the concentration of attached biomass presented a weakly increase with reactor substrate concentration (from 3.10 g VS l-1 to 4.54 g VS l-1 for 32 and 1150 mg COD l-1 respectively). On the other hand when reducing , a sharp incrase in biomass loss coefficient was observed showing that excess biofilm growth was continuously removed by shearing forces. Thus in the assayed conditions the attached biomass concentration was basically determined by the bed superficial velocity. Result show that diffusional resistances are negligible. Data are fairly well correlated by a variable order kinetic model. The apparent reaction order is a function of temperature and increases from 0.27 to 0.7 when temperature decreases from 35° C to 13°C.Nomenclature b Total biomass loss coefficient (T-1) - J Flux of substrate removal into the biofilm surface (ML-2 T-1) - J d Flux of substrate removed into the biofilm surface in deep conditions (ML-2 T-1) - k Maximum specific rate of substrate utilization (T-1) - K Variable order kinetic constant (T-1 Mn-1 L3n-3) - K s9 Hall saturation constant (ML-3) - n Reaction order - q Feed flow rate (L3 T-1) - S Substrate concentration (ML-3) - Se Effluent substrate concentration (ML-3) - So Influent substrate concentration (ML-3) - Semin Minimum substrate concentration able to sustain a steady-state biofilm (ML-3) - T Temperature - t Time(T) - V Bed volume (L3) - VS Volatile solids (M) - VSS Volatile suspended solids - X Attached biomass concentration (ML-3) - X c Effluent volatile suspended solids (ML-3) - Y Yield coefficient - Hydraulic retention time (T) This work forms part of a Doctoral Thesis of senior author  相似文献   

8.
Summary Equations are described which relate nutrient feed rate to specific microbial growth rate in fed batch culture. Fed batch cultures are classified into three types: 1) those allowing constant specific microbial growth rate, 2) those in which the rate of change of flow rate is constant and 3) those in which the nutrient flow rate is constant. The basic properties of these three types are described.Symbols F medium flow rate, L3 T–1 - F o medium flow rate at zero time, L3 T–1 - g rate of change of flow rate with time, L3 T–2 - K v volume constant, being the total cell weight at zero time divided by the product of the yield coefficient and growth-limiting substrate concentration in the feed, L3 - s r growth limiting substrate concentration in the feed, ML–3 - V volume of liquid in the growth vessel, L3 - V f volume of medium fed to the growth vessel, L3 - V o volume of liquid in the growth vessel at zero time, L3 - X total weight of cells, M - x concentration of cells, ML–3 - X g total weight of cells grown, M - X o total weight of cells at zero time, M - Y yield coefficient, weight of cells grown per unit weight of growth-limiting substrate - specific microbial growth rate, T–1  相似文献   

9.
G. O. Kirst  M. A. Bisson 《Planta》1982,155(4):287-295
Ionic responses to alteration in external and internal pH were examined in an organism from a marine-like environment. Vacuolar pH (pHv) is about 4.9–5.1, constant at external pH (pHo) 5–8, while cytoplasmic pH (pHc) increases from 7.3 to 7.7. pHc regulation fails above pHo 9, and this is accompanied by failure of turgor regulation. Na+ increases above pHo 9, while K+ and Cl decrease. These changes alone cannot however explain the alterations in turgor. Agents known to affect internal pH are also tested for their effect on ion relations.Abbreviations Ci ion concentration - CCCP carbonyl cyanide m-chlorophenyl hydrazone - DCCD dicyclohexylcarbodiimide - DES diethylstilbestrol - DMO 5,5-dimethyloxazolidine-2,4-dione - DNP 2,4-dinitrophenol - pHo external pH - pHc cytoplasmic pH - pHv vacuolar pH - i osmotic pressure - turgor pressure  相似文献   

10.
Summary The kinetics ofBordetella pertussis growth was studied in a glutamate-limited continuous culture. Growth kinetics corresponded to Monod's model. The saturation constant and maximum specific growth rate were estimated as well as the energetic parameters, theoretical yield of cells and maintenance coefficient. Release of pertussis toxin (PT) and lipopolysaccharide (LPS) were growth-associated. In addition, they showed a linear relationship between them. Growth rate affected neither outer membrane proteins nor the cell-bound LPS pattern.Nomenclature X cell concentration (g L–1) - specific growth rate (h–1) - m maximum specific growth rate (h–1) - D dilution rate (h–1) - S concentration of growth rate-limiting nutrient (glutamate) (mmol L–1 or g L–1) - Ks substrate saturation constant (mol L–1) - ms maintenance coefficient (g g–1 h–1) - Yx/s theoretical yield of cells from glutamate (g g–1) - Yx/s yield of cells from glutamate (g g–1) - YPT/s yield of soluble PT from glutamate (mg g–1) - YKDO/s yield of cell-free KDO from glutamate (g g–1) - YPT/x specific yield of soluble PT (mg g–1) - YKDO/x specific yield of cell-free KDO (g g–1) - qPT specific soluble PT production rate (mg g–1 h–1) - qKDO specific cell-free KDO production rate (g g–1 h–1)  相似文献   

11.
Summary The ethanol yield was not affected and the ethanol productivity increased (10%) when linearly decreasing feeding rates were used instead of constant feeding rates in fed-batch ethanol fermentations.Nomenclature F reactor feeding rate (L.h–1) - ME mass of ethanol in the fermentor (g) - Ms mass of TRS in the fermentor (g) - Mx mass of yeast cells (dry matter) in the fermentor (g) - P ethanol productivity (g.L–1.h–1) - s standard deviation - So TRS concentration in the feeding mash (g.L–1) - t time (h) - T fermentor filling-up time (h) - TRS total reducing sugars calculated as glucose (g.L–1) - Xo yeast cells concentration (dry matter) in the inoculum (g.L–1) - average ethanol yield (% of the theoretical value)  相似文献   

12.
Studies in tower reactors with viscous liquids on flow regime, effective shear rate, liquid mixing, gas holdup and gas/ liquid mass transfer (k La) are reviewed. Additional new data are reported for solutions of glycerol, CMC, PAA, and xanthan in bubble columns with diameters of 0.06, 0.14 and 0.30 m diameter. The wide variation of the flow behaviour index (1 to 0.18) allows to evaluate the effective shear rate due to the gas flow. New dimensionless correlations are developed based on the own and literature data, applied to predict k La in fermentation broths, and compared to other reactor types.List of Symbols a(a) m–1 specific interfacial area referred to reactor (liquid) volume - Bo Bond number (g D c 2 L/) - c L(c L * ) kmol m–3 (equilibrium) liquid phase oxygen concentration - C coefficient characterising the velocity profile in liquid slugs - C s m–1 coefficient in Eq. (2) - d B(dvs) m bubble diameter (Sauter mean of d B) - d 0 m diameter of the openings in the gas distributor plate - D c m column diameter - D L m2s–1 diffusivity - E L(EW) m2 s–1 dispersion coefficient (in water) - E 2 square relative error - Fr Froude number (u G/(g Dc)0.5) - g m s–2 gravity acceleration - Ga Gallilei number (g D c 3 L 2 / eff 2 ) - h m height above the gas distributor the gas holdup is characteristic for - k Pasn fluid consistency index (Eq. 1) - k L m s–1 liquid side mass transfer coefficient - k La(kLa) s–1 volumetric mass transfer coefficient referred to reactor (liquid) volume - L m dispersion height - n flow behaviour index (Eq. 1) - P W power input - Re liquid slug Reynolds number ( L(u G +u L) D c/eff) - Sc Schmidt number ( eff/( L D L )) - Sh Sherwood number (k La D c 2 /DL) - t s time - u B(usw) m s–1 bubble (swarm) rise velocity - u G(uL) m s–1 superficial gas (liquid) velocity - V(VL) m3 reactor (liquid) volume Greec Symbols W m–2 K–1 heat transfer coefficient - y(y eff) s–1 (effective) shear rate - G relative gas holdup - s relaxation time of viscoelastic liquid - L(eff) Pa s (effective) liquid viscosity (Eq. 1) - L kg m–3 liquid density - N/m surface tension  相似文献   

13.
A new indigenous soil bacterium Pseudomonas sp. growing on phenol and on a mixture of phenol, toluene, o-cresol, naphthalene and 1,2,3-trimethylbenzene (1,2,3-TMB) was isolated and characterized. Phylogenetic analysis suggested its classification to Pseudomonadaceae family and showed 99.8% DNA sequence identity to Pseudomonas pseudoalcaligenes species. The isolate was psychrotroph, with growth temperatures ranging from ca. 0 to 40 °C. The GC–MS structural analysis of metabolic products of phenol degradation by this microorganism indicated a possible ortho cleavage pathway for high concentrations (over 200 mg L–1) of phenol. Biodegradation rates by this species were found to be three times more effective than those previously reported by other Pseudomonas strains. The effect of temperature on phenol degradation was studied in batch cultures at temperatures ranging from 10 to 40°C and different initial phenol concentrations (up to 500mgL–1). Above 300mgL–1 of initial phenol concentration no considerable depletion was recorded at both 10 and 40°C. Maximum degradation rates for phenol were recorded at 30°C. The biodegradation rate of phenol was studied also in the presence of additional carbon sources (o-cresol, toluene, naphthalene, 1,2,3-TMB) at the optimum growth temperature and was found significantly lower by a factor of eight in respect to the strong competitive inhibition between the substrates and the more available sources of carbon and energy. The Haldane equation =m S/(KS+S+S2/KI) was found to best fit the experimental data at the optimum temperature of 30°C than the Monod equation with kinetic constants m=0.27h–1, KS=56.70mgL–1, KI=249.08mgL–1.  相似文献   

14.
Methods of intrinsic viscosity () and beam flow birefringence were used to study the effects of some single-charged ions (F, Cl, Br, I, NO 2, NO 3, ClO 4, SCN, CH3COO) on the size and thermodynamic rigidity of a DNA molecule in aqueous solutions of sodium salts in a broad interval of ionic strength when temperature T is changed. It has been shown that the close interactions in a macromolecule and the resulting DNA persistent length a are independent of the type of the salt anion over the whole interval of . On the contrary, the specific volume of the DNA molecule in solution, proportional to the value, is quite sensitive to the anionic composition of the solvent, which is due to the effect of anions and their hydration on the long-range interactions in the macromolecule. The presence of polyatomic and halide anions is manifested differently in the value of DNA. Possible factors responsible for the observed effect and the role of structural alterations of water upon anion hydration are discussed.  相似文献   

15.
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   

16.
The turgor-homeostat model of assimilate efflux from coats of developing seed of Phaseolus vulgaris L. was further characterised. The turgor pressure (P), the volumetric elastic modulus () and hydraulic conductivity (Lp) of the seed coat cells responsible for assimilate efflux and cotyledon storage parenchyma cells were determined with a pressure probe. In addition, turgor of the seed coat and cotyledons was estimated by measuring the osmolalities of symplastic and apoplastic fluids extracted by centrifugation. Osmolality of symplastic and apoplastic saps collected from the seed coat declined significantly over the period of seed development from a cotyledon water content of 80% to 50%. However, the difference in osmolalities of the apoplastic and symplastic saps remained relatively constant. For cotyledons, osmolality of the apoplastic sap exhibited a significant decline during seed development, while the osmolality of symplastic sap did not change significantly. Hence cotyledon P increased as the water content dropped from 80% to 50%. For both detached and attached empty seed coats, a small decrease (ca. 40mOsmol·kg–1) in the osmolality of the bathing solution, led to a rapid increase in P of cells involved in assimilate efflux (efflux cells) by about 0.07 MPa. Thereafter, cell P exhibited a rapid decline to the original value within some 20–30 min. When P of the efflux cells was reduced by increasing the osmolality of the bathing solution, P exhibited a comparable rate of recovery for attached empty seed coats but there was no P recovery to its original value in the case of detached seed coats. In contrast, the cotyledon storage parenchyma cells did not exhibit P regulation when the osmolality of the bathing solution was changed. The observations that the efflux cells of P. vulgaris seed coats can rapidly adjust their P homeostatically in response to small changes in apoplastic osmolality are consistent with the operation of a turgor-homeostat mechanism. The volumetric elastic modulus () of the seed coat efflux cells exhibited a mean value of 7.3±0.8 MPa at P=0.15 MPa and was found to be linearly dependent on cell P. The e of the cotyledon storage parenchyma cells was estimated to be 6.1±1.0 MPa at P=0.41 MPa. Hydraulic conductivity (Lp) of the seed coat cells and the cotyledon cells was (8.2±1.5) × 10–8m·s–1·MPa–1and (12.8±1.0) × 10–8 m·s–1·MPa–1, respectively. The relatively high , i.e., low elasticity, for the seed coat cell walls would ensure that small changes in water potential of the seed apoplast will be reflected in large changes in cell P. The high Lp values for both the seed coat and the cotyledon cells is consistent with the rapid changes in P in response to changes in water potential of the seed apoplast.Abbreviations LYCH Lucifer Yellow CH - volumetric elastic modulus - Lp hydraulic conductivity - P turgor pressure - osmotic pressure - t1/2 half-time for water exchange The investigation was supported by funds from the Australian Research Council. We are grateful to Louise Hetherington for competent technical assistance and to Kevin Stokes for raising the plant material.  相似文献   

17.
Jia  Yinsuo  Gray  V.M. 《Photosynthetica》2003,41(4):605-610
We determined for Vicia faba L the influence of nitrogen uptake and accumulation on the values of photon saturated net photosynthetic rate (P Nmax), quantum yield efficiency (), intercellular CO2 concentration (C i), and carboxylation efficiency (C e). As leaf nitrogen content (NL) increased, the converged onto a maximum asymptotic value of 0.0664±0.0049 mol(CO2) mol(quantum)–1. Also, as NL increased the C i value fell to an asymptotic minimum of 115.80±1.59 mol mol–1, and C e converged onto a maximum asymptotic value of 1.645±0.054 mol(CO2) m–2 s–1 Pa–1 and declined to zero at a NL-intercept equal to 0.596±0.096 g(N) m–2. fell to zero for an NL-intercept of 0.660±0.052 g(N) m–2. As NL increased, the value of P Nmax converged onto a maximum asymptotic value of 33.400±2.563 mol(CO2) m–2 s–1. P N fell to zero for an NL-intercept of 0.710±0.035 g(N) m–2. Under variable daily meteorological conditions the values for NL, specific leaf area (L), root mass fraction (Rf), P Nmax, and remained constant for a given N supply. A monotonic decline in the steady-state value of Rf occurred with increasing N supply. L increased with increasing N supply or with increasing NL.  相似文献   

18.
Severely yellowed ten-year-old spruce trees growing in the Vosges Mountains on an acidic soil were fertilised with Magnesium lime during the spring of 1990. The effects of this treatment were assessed 18 months later. A very significant improvement of the mineral status of the trees was detected, with increasing Mg contents in the needles, and as a consequence, reduced yellowing and improved chlorophyll content. Only slight differences with control trees were observed for height increase. Effects of this improved nutrition on photosynthesis were tested measuring net CO2 assimilation rates and chlorophyll a fluorescence. Light-saturated net assimilation rates of current-year needles were high, reaching 5.3 mol m–2 s–1 on a total needle area basis. The improvement in chlorophyll and Mg content had no significant effect on net assimilation rates or on any parameter describing photochemical functions of both current-and previous-year needles. Despite the strong inter-individual variability in needle chlorophyll and Mg contents (ranging from 0.2 to 0.8 mg g–1 fresh weight, and 0.05 to 0.5 mg g-1 dry weight respectively), photochemical efficiency of PS II under limiting irradiance only decreased significantly on older needles displaying Mg contents below 0.1 mg g–1. It is concluded from these results that spruce trees exhibit a high degree of plasticity with regard to Mg deficiency on acidic soils, and that improved Mg nutrition and increased chlorophyll content do not necessarily improve photosynthesis and height growth.Abbreviations A light-saturated net CO2 assimilation rate (mol m–2 s–1) - gw light-saturated needle conductance to water vapour (mmol m–2 s–1) - wp and wm pre-dawn and mid-day needle water potential (MPa) - osmotic potential of sap expressed from needles (MPa) - PFD photosynthetic photon flux density (mol m–2 s–1) - Fv/Fm photochemical efficiency of PS II after 20 min dark adaptation - F/Fm ' photochemical efficiency of PS II reaction centres after 10 min at a PFD of 220 mol m–2 s–1  相似文献   

19.
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   

20.
Some of the largest riverine N fluxes in the continental USA have been observed in agricultural regions with extensive artificial subsurface drainage, commonly called tile drainage. The degree to which high riverine N fluxes in these settings are due to high net N inputs (NNI), greater transport efficiency caused by the drainage systems, or other factors is not known. The objective of this study was to evaluate the role of tile drainage by comparing NNI and riverine N fluxes in regions of Illinois with similar climate and crop production practices but with different intensities of tile drainage. Annual values of NNI between 1940 and 1999 were estimated from county level agricultural production statistics and census estimates of human population. During 1945–1961, riverine nitrate flux in the extensively tile drained region averaged 6.6kgNha–1year–1 compared to 1.3 to 3.1kgNha–1 for the non-tile drained region, even though NNI was greater in the non-tile drained region. During 1977–1997, NNI to the tile-drained region had increased to 27kgNha–1year–1 and riverine N flux was approximately 100% of this value. In the non-tile-drained region, NNI was approximately 23kgNha–1year–1 and riverine N flux was between 25% and 37% of this value (5 to 9kgNha–1year–1). Denitrification is not included in NNI and, therefore, any denitrification losses from tile-drained watersheds must be balanced by other N sources, such as depletion of soil organic N or underestimation of biological N fixation. If denitrification and depletion of soil organic N are significant in these basins, marginal reductions in NNI may have little influence on riverine N flux. If tile drained cropland in Illinois is representative of the estimated 11 million ha of tile drained cropland throughout the Mississippi River Basin, this 16% of the drainage area contributed approximately 30% of the increased nitrate N flux in the Lower Mississippi River that occurred between 1955 and the 1990s.  相似文献   

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