Diffusivity of oxygen in aerobic granules

This work for the first time estimated apparent oxygen diffusivity (D(app)) of two types of aerobic granules, acetate-fed and phenol-fed, by probing the dissolved oxygen (DO) level at the granule center with a sudden change in the DO of the bulk liquid. With a high enough flow velocity across the granule to minimize the effects of external mass transfer resistance, the diffusivity coefficients of the two types of granules were estimated with reference to a one-dimensional diffusion model. The carbon source has a considerable effect on the granule diameter (d) and the oxygen diffusivity. The diffusivity coefficients were noted 1.24-2.28 x 10(-9) m2/s of 1.28-2.50 mm acetate-fed granules, and 2.50-7.65 x 10(-10) m2/s of 0.42-0.78 mm phenol-fed granules. Oxygen diffusivity declined with decreasing granule diameter, in particular, the diffusivity of acetate-fed granules is proportional to the size, whereas the diffusivity of phenol-fed granules is proportional to the square of granule diameter. The existence of large pores in granule, evidenced by FISH-CLSM imaging, was proposed to correspond to the noted size-dependent oxygen diffusivity. The phenol-fed granules exhibited a higher excellular polymer (ECP) content than the acetate-fed granules, hence yielding a lower oxygen diffusivity.     

Solasodine production from self-immobilised Solanum aviculare cells.

Procedures were developed for 'self-immobilisation' of Solanum aviculare cells to eliminate the need for artificial immobilisation supports. Depending on the cytokinin used in liquid medium, compact aggregates 0.4-2.0 cm in diameter were formed without dispersed cells also being present. Histochemical analysis showed that the aggregates were structurally organised to facilitate nutrient transport. Growth, sugar uptake and solasodine production were measured in shake-flask cultures. Most of the product was stored in the aggregates to reach a maximum concentration of 0.3% dry weight; this is between 1.5 and 10 times the levels reported for suspended cells under similar conditions. A substantial amount of solasodine was produced after growth ceased. The maximum rate of solasodine production was about 0.22 mg g-1 d-1. A simple air-driven bioreactor was tested for culture of the aggregates; solasodine yields were comparable to those measured in shake flasks.     

Oxygen transfer properties of bubbles in animal cell culture media

Oxygen transfer rates were determined in a bubble aerated animal cell bioreactor. It was found that the oxygen transfer rates increased in the following order: large bubbles ( approximately 5 mm diameter) < intermediate bubbles ( approximately 1 mm diameter) < micron-sized bubbles ( approximately 100 mum diameter). Under certain conditions, the micron-sized bubbles were capable of achieving oxygen transfer rate up to 100 h(-1), a 10-20-fold higher transfer rate than the large bubbles. The effects of medium composition on oxygen transfer rates were different for the three ranges of bubbles studied. For the large bubbles, oxygen transfer rates decreased with increasing medium complexity. The lowest oxygen transfer rate was found in new-born calf serum (NBCS) and/or Pluronic F-68 supplemented media. For the intermediate and micron-sized bubbles, supplementation with NBCS into the culture media resulted in decreased oxygen transfer rate. However, further supplementation with Pluronic F-68 enhanced oxygen transfer rate greatly for both types of bubbles. The highest oxygen transfer rate was found for micron-sized bubbles in Pluronic F-68 supplemented media containing antifoam agent and NBCS.     

Diffusivity of oxygen into carriers entrapping whole cells

The effective diffusivity of oxygen, D(e), in Ca-alginate and PVA-SbQ gels was measured using a two-chamber vessel with a membrane between the two chambers. The effect of cell density, C(c), on D(e) in Ca-alginate gels was studied. The effective diffusivity of oxygen decreased with increasing cell density, to C(c) = 170 kg dry cells/m(3) gel. The dependency of D(e) on cell density was discussed in terms of a random-pore model. The model correlated well with experimental data, i.e., kD(e)/D(0) = 0.86(1 - 1.47 x 10(-3) C(c))(2). Here, k is the partition coefficient, and D(0) is diffusivity in water.     

Extraction of polyphenols from white distilled grape pomace: optimization and modelling

Both ethanolic and aqueous extraction were carried out in a laboratory-scale vertical extractor to obtain polyphenols from distilled grape pomace of Vitis vinifera var. "Albari?o". An experimental design was performed to analyse the effects of flow (2 ml/min and 4 ml/min) and temperature (40 degrees C and 50 degrees C). Yields of polyphenolics from aqueous extraction were much higher (up to 30-fold) than those of ethanolic extraction, in contrast with previous results obtained by us from batch extraction of different grape varieties. Polyphenols extraction was modelled by application of second Fick's law to spherical particles of 0.5 mm diameter, so obtaining the effective diffusion coefficient as parameter. The mass transfer coefficients were also estimated, giving as result that the external mass transfer resistance was negligible. Correlation coefficients ranged 0.989-0.9999. Effective diffusivity values in water extraction assays were between 0.6x10(-11) m(2)/s and 2.1x10(-11) m(2)/s. Using ethanol as solvent, the effective diffusivity was lower, between 0.1x10(-11) m(2)/s and 0.76x10(-11) m(2)/s.     

Oxygen requirements and mass transfer in hairy-root culture

Oxygen mass transfer in clumps of Atropa belladonna hairy roots was investigated as a function of root density and external flow conditions. Convection was the dominant mechanism for mass transfer into root clumps 3.5 to 5.0 cm in diameter; Peclet numbers inside the clumps ranged from 1.4 x 10(3) to 7.1 x 10(4) for external superficial flow velocities between 0.4 and 1.4 cm s(-1). Local dissolved-oxygen levels and rates of oxygen uptake were measured in aflow chamber and in bubble column and stirred bioreactors. When air was used as oxygen source, intraclump dissolved-oxygen tensions ranged from90% to 100% air saturation at high external flow velocity andlow root density, to less than 20% air saturation in dense root clumps. Specific oxygen-uptake rate declined with increasing root density. When external boundary layers around individual roots were eliminated byforcing liquid through the clumps at superficial velocities between 0.2 and1.0 cm s(-1), internal dissolved-oxygen tension was maintained at 95% to 100% air saturation and rate of oxygen uptake at 1.6 x 10(-6) g g(-1) s(-1) dry weight. Liquid culture of single A. belladonna hairy roots was used to investigate the effect of dissolved-oxygen tensionon root growth and morphology. Total root length and number of root tips increased exponentially at oxygen tensions between 70% and 100%air saturation. Specific growth rate increased with oxygen tension up to 100% air saturation; this result demonstrates that hairy roots aeratedwithout oxygen supplementation are likely to be oxygenlimited. No growth occurred at 50% air saturation. Growth of hairy roots proceeded with an average length per tip of about 1 cm; this value was essentially independent of dissolved-oxygen tension between 70% and 100% air saturation. (c) 1994 John Wiley & Sons, Inc.     

Determination of diffusion coefficients and diffusion characteristics for chlorferon and diethylthiophosphate in Ca-alginate gel beads

Diffusion characteristics of chlorferon and diethylthiophosphate (DETP) in Ca-alginate gel beads were studied to assist in designing and operating bioreactor systems. Diffusion coefficients for chlorferon and DETP in Ca-alginate gel beads determined at conditions suitable for biodegradation studies were 2.70 x 10(-11) m(2)/s and 4.28 x 10(-11) m(2)/s, respectively. Diffusivities of chlorferon and DETP were influenced by several factors, including viscosity of the bulk solution, agitation speed, and the concentrations of diffusing substrate and immobilized cells. Diffusion coefficients increased with increasing agitation speed, probably due to poor mixing at low speed and some attrition of beads at high speeds. Diffusion coefficients also increased with decreasing substrate concentration. Increased cell concentration in the gel beads caused lower diffusivity. Theoretical models to predict diffusivities as a function of cell weight fraction overestimated the effective diffusivities for both chlorferon and DETP, but linear relations between effective diffusivity and cell weight fraction were derived from experimental data. Calcium-alginate gel beads with radii of 1.65-1.70 mm used in this study were not subject to diffusional limitations: external mass transfer resistances were negligible based on Biot number calculations and effectiveness factors indicated that internal mass transfer resistance was negligible. Therefore, the degradation rates of chlorferon and DETP inside Ca-alginate gel beads were reaction-limited.     

Experimental study of a ceramic microsparging aeration system in a pilot-scale animal cell culture

The oxygen supply of cell cultures with the aid of free gas bubbles is an efficient process strategy in pharmaceutical production. If the cell-damaging impact of gas bubbles is reduced, direct aeration becomes a practical solution with scale-up potential and comparatively high oxygen transfer rates. In this paper a microsparging aeration system made of porous ceramic was compared with bubble-free membrane aeration. The sparging system was used for the long-term cultivation of mammalian cells in 2- to 100-L scale bioreactors and produced bubble sizes of 100-500 microm in diameter. Using a scale of 2.5 and 30 L, a cell density of 2.6 x 10(6) cells/mL was attained. When a 100-L scale was used, a density of 1.1 x 10(6) cells/mL was achieved, whereas a comparable membrane-aerated system showed a cell density of 2.2 x 10(6) cells/mL. At relatively low agitation rates of less than 70 rpm in the sparged bioreactors, a homogeneous and constant oxygen concentration was kept in the medium. As a result of the different foam-forming tendency caused by the lower gas flow of the ceramic sparger compared to that of the standard aeration systems, we were able to develop an appropriate process control strategy. Furthermore, oxygen transfer measurements for the common stainless steel sparger and the ceramic sparger showed a 3-fold higher oxygen transfer coefficient for the ceramic sparger.     

旱地施有机肥对土壤有机质和水稳性团聚体的影响

通过渭北旱塬2007-2010年田间定位试验,研究了有机肥不同施用量(低量7500 kg·hm^-2、中量15000 kg·hm^-2、高量22500 kg·hm^-2)对连作玉米地土壤有机质、团聚体各层粒径分布和稳定性的影响.结果表明：0～20 cm土层,高量有机肥处理土壤有机质含量较低量有机肥处理提高4.1%～4.6%,高、中量有机肥处理较对照提高4.6%～11.2%,低量有机肥处理在施肥第4年（2010年）较CK提高4.7%～6.3%.0～30 cm土层,所有有机肥处理>5 mm水稳性团聚体的增幅最大,其含量随有机肥用量的增加而显著升高;有机肥处理显著提高了土壤>0.25 mm水稳性团聚体含量、团聚体平均质量直径和团聚体稳定率,且随有机肥用量的增加而显著增加;中、高量有机肥处理比单施化肥处理增加效果显著.     

Oxygen gradients in tissue-engineered PEGT/PBT cartilaginous constructs: measurement and modeling

The supply of oxygen within three-dimensional tissue-engineered (TE) cartilage polymer constructs is mainly by diffusion. Oxygen consumption by cells results in gradients in the oxygen concentration. The aims of this study were, firstly, to identify the gradients within TE cartilage polymer constructs and, secondly, to predict the profiles during in vitro culture. A glass microelectrode system was adapted and used to penetrate cartilage and TE cartilaginous constructs, yielding reproducible measurements with high spatial resolution. Cartilage polymer constructs were cultured for up to 41 days in vitro. Oxygen concentrations, as low as 2-5%, were measured within the center of these constructs. At the beginning of in vitro culture, the oxygen gradients were steeper in TE constructs in comparison to native tissue. Nevertheless, during the course of culture, oxygen concentrations approached the values measured in native tissue. A mathematical model was developed which yields oxygen profiles within cartilage explants and TE constructs. Model input parameters were assessed, including the diffusion coefficient of cartilage (2.2 x 10(-9)) + (0.4 x 10(-9) m(2) s(-1)), 70% of the diffusion coefficient of water and the diffusion coefficient of constructs (3.8 x 10(-10) m(2) s(-1)). The model confirmed that chondrocytes in polymer constructs cultured for 27 days have low oxygen requirements (0.8 x 10(-19) mol m(-3) s(-1)), even lower than chondrocytes in native cartilage. The ability to measure and predict local oxygen tensions offers new opportunities to obtain more insight in the relation between oxygen tension and chondrogenesis.     

Kinetics of biodegradation of p-xylene and naphthalene and oxygen transfer in a novel airlift immobilized bioreactor

The scope of this study included the biodegradation performance and the rate of oxygen transfer in a pilot-scale immobilized soil bioreactor system (ISBR) of 10-L working volume. The ISBR was inoculated with an acclimatized population of contaminant degrading microorganisms. Immobilization of microorganisms on a non-woven polyester textile developed the active biofilm, thereby obtaining biodegradation rates of 81 mg/L x h and 40 mg/L x h for p-xylene and naphthalene, respectively. Monod kinetic model was found to be suitable to correlate the experimental data obtained during the course of batch and continuous operations. Oxygen uptake and transfer rates were determined during the batch biodegradation process. The dynamic gassing-out method was used to determine the oxygen uptake rate (OUR) and volumetric oxygen mass transfer, K(L) a. The maximum volumetric OUR of 255 mg O(2)/L x h occurred approximately at 720-722 h after inoculation, when the dry weight of biomass concentration was 0.67 g/L.     

Scale-up of breast cancer stem cell aggregate cultures to suspension bioreactors

It has been hypothesized that breast tumor formation results from the activity of a scarce population of cells known as Breast Cancer Stem Cells (BrCSCs) and that the development of effective breast cancer therapies may therefore ultimately rely upon the ability to effectively target these cells for eradication. The scarcity of BrCSCs in vivo severely compromises research on these populations, as analyses are restricted to those requiring small cell numbers, and has become a major impediment to the development of therapeutic strategies against breast cancer. Through the culture of murine tissue aggregates containing a population of BrCSCs, this study demonstrates the ability of propagating this scarce population in a controlled and reproducible manner, within suspension bioreactors. A rigorous theoretical framework has been developed in order to understand and characterize the implications of oxygen mass transfer within aggregates upon scale-up and thereby provide a foundation for the scale-up of aggregate cultures. A two-factor, two-level factorial experimental design was also performed in order to assess the effects of inoculation density and hydrodynamic shear upon cell yield. We discovered that the culture of the murine aggregates in a relatively low shear environment (tau(max) = 0.20 Pa) and inoculated at 3.50 x 10(4) cells/mL resulted in the best yields for the range of conditions investigated in suspension bioreactors. A detailed study on the oxygen uptake kinetics of the aggregates also revealed that the uptake rates were not significantly affected by mass transfer limitations, as uptake rates of aggregate cultures were found to be comparable to those observed in single cell cultures. Cells propagated in a process controlled 500 mL suspension bioreactor resulted in growth kinetics that were comparable to those observed in 125 mL bioreactors. Doubling times in the 500 mL vessel were found to be 23.9 h and attained a maximum cell density of 1.20 x 10(6) cells/mL. After enumerating the number of BrCSCs, this resulted in an approximately 20-fold increase in BrCSC numbers in batch suspension cultures. With greater attention being applied to BrCSCs, their propagation in suspension bioreactors makes available experimental avenues that are not currently accessible and may thereby enable the development of more effective therapeutic drugs for the treatment of breast cancer.     

A quantitative framework for the design of acellular hemoglobins as blood substitutes: implications of dynamic flow conditions

The delivery of oxygen to tissue by cell-free carriers eliminates intraluminal barriers associated with red blood cells. This is important in arterioles, since arteriolar tone controls capillary perfusion. We describe a mathematical model for O(2) transport by hemoglobin solutions and red blood cells flowing through arteriolar-sized tubes to optimize values of p50, Hill number, hemoglobin molecular diffusivity and concentration. Oxygen release is evaluated by including an extra-luminal resistance term to reflect tissue oxygen consumption. For low consumption (i.e., high resistance to O(2) release) a hemoglobin solution with p50=15 mmHg, n=1, D(HBO2)=3 x 10(-7) cm(2)/s delivers O(2) at a rate similar to that of red blood cells. For high consumption, the p50 must be decreased to 5 mmHg. The model predicts that regardless of size, hemoglobin solutions with higher p50 will present excess O(2) to arteriolar walls. Oversupply of O(2) to arteriolar walls may cause constriction and paradoxically reduced capillary perfusion.     

Oxygen diffusion through zoogloeal flocs

The mechanism of oxygen transfer through a pure culture floc of Zoogloea ramigera I-16M has been described quantitatively. Oxygen uptake rates for both blended and nonblended floc particles indicated that, at a certain dissolved oxygen concentration, diffusion of oxygen through the floc matrix was the mechanism controlling the rate of oxygen utilization by the floc. This mechanism was quantitatively described by determining the oxygen diffusivity values for the floc. The diffusional distances of the floc particles along with the oxygen utilization rates of the floc were measured on floc grown under various conditions. Anoxic core equations were then used to calculate the oxygen diffusivity values for each experiment. These diffusivity values were then used to estimate the oxygen concentrations necessary in activated sludge plants.     

Noninvasive imaging of the distribution in oxygen in tissue in vivo using near-infrared phosphors.

A newly developed water-soluble phosphor suitable for measuring oxygen pressure in the blood (Green 2W) was used for noninvasive, in vivo imaging of oxygen distribution in the vascular systems of mice. Oxygen quenches the phosphorescence of Green 2W, measured in the presence of 2% albumin, according to the Stern-volmer relationship. This oxygen-dependent quenching of phosphorescence has been used to obtain digital maps of the oxygen distribution in the tissue vasculature. EMT-6 mammary carcinoma tumors were grown by injecting 1 x 10(6) cells in 0.1-ml carrier into the subcutaneous space over the muscle on the hindquarter. When the tumors were approximately 8 mm in diameter, 300 micrograms of phosphorescence probe (Green 2W; absorption maximum 636 nm) was injected into the tail vein. The mice were immobilized with intraperotoneal Ketamine (133 mg/kg) and Xylazine (10 mg/kg) and illuminated with flashes (< 4-microseconds t1/2) of light of 630 +/- 12 nm. The emitted phosphorescence (790-nm maximum) was imaged an intensified CCD camera. Images were collected beginning at 30, 50, 80, 120, 180, 240, 420, and 2500 microseconds after the flash and used to calculate digital maps of the phosphorescence lifetimes and oxygen pressure. Both the illumination light and the phosphorescence were in the near-infrared region of the spectrum, where tissue has greatly decreased absorbance. The light therefore readily passed through the skin and centimeter thicknesses of tissue. The oxygen maps could be obtained by illuminating from the side of the mouse opposite the camera (and tumor). The tumors were readily observed as regions with oxygen pressures substantially below those of the surrounding tissue. Thus, phosphorescence measurements can noninvasively detect volumes of tissue with below-normal oxygen pressure in the presence of much larger volumes of tissue with normal oxygen pressures. In addition, tissue oxygen pressures can be monitored in real time, even through centimeter thicknesses of tissue.     

Studies on the respiration rate of free and immobilized cells of Cephalosporium acremonium in cephalosporin C production

Bioprocesses using filamentous fungi immobilized in inert supports present many advantages when compared to conventional free cell processes. However, assessment of the real advantages of the unconventional process demands a rigorous study of the limitations to diffusional mass transfer of the reagents, especially concerning oxygen. In this work, a comparative study was carried out on the cephalosporin C production process in defined medium containing glucose and sucrose as main carbon and energy sources, by free and immobilized cells of Cephalosporium acremonium ATCC 48272 in calcium alginate gel beads containing alumina. The effective diffusivity of oxygen through the gel beads and the effectiveness factors related to the respiration rate of the microorganism were determined experimentally. By applying Monod kinetics, the respiration kinetics parameters were experimentally determined in independent experiments in a complete production medium. The effectiveness factor experimental values presented good agreement with the theoretical values of the approximated zero‐order effectiveness factor, considering the dead core model. Furthermore, experimental results obtained with immobilized cells in a 1.7‐L tower bioreactor were compared with those obtained in 5‐L conventional fermentor with free cells. It could be concluded that it is possible to attain rather high production rates working with relatively large diameter gel beads (ca. 2.5 mm) and sucrose consumption‐based productivity was remarkably higher with immobilized cells, i.e., 0.33 gCPC/kg sucrose/h against 0.24 gCPC/kg sucrose/h in the aerated stirred tank bioreactor process. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 63: 593–600, 1999.     

Hydrocarbon biodegradation in oxygen-limited sequential batch reactors by consortium from weathered, oil-contaminated soil

We studied the use of sequential batch reactors under oxygen limitation to improve and maintain consortium ability to biodegrade hydrocarbons. Air-agitated tubular reactors (2.5 L) were operated for 20 sequential 21-day cycles. Maya crude oil-paraffin mixture (13,000 mg/L) was used as the sole carbon source. The reactors were inoculated with a consortium from the rhizosphere of Cyperus laxus, a native plant that grows naturally in weathered, contaminated soil. Oxygen limitation was induced in the tubular reactor by maintaining low oxygen transfer coefficients (k(L)a < 20.6 h(-1)). The extent and biodegradation rates increased significantly up to the fourth cycle, maintaining values of about 66.33% and 460 mg x L(-1) x d(-1), respectively. Thereafter, sequential batch reactor operation exhibited a pattern with a constant general trend of biodegradation. The effect of oxygen limitation on consortium activity led to a low biomass yield and non-soluble metabolite (0.45 g SS/g hydrocarbons consumed). The average number of hydrocarbon-degrading microorganisms increased from 6.5 x 10(7) (cycles 1-3) to 2.2 x 10(8) (cycles 4-20). Five bacterial strains were identified: Achromobacter (Alcaligenes) xylosoxidans, Bacillus cereus, Bacillus subtilis, Brevibacterium luteum, and Pseudomonas pseudoalcaligenes. Asphaltene-free total petroleum hydrocarbons, extracted from a weathered, contaminated soil, were also biodegraded (97.1 mg x L(-1) x d(-1)) and mineralized (210.48 mg CO2 x L(-1) x d(-1)) by the enriched consortium without inhibition. Our results indicate that sequential batch reactors under oxygen limitation can be used to produce consortia with high and constant biodegradation ability for industrial applications of bioremediation.     

Oxygen release from arterioles with normal flow and no-flow conditions.

The rate of oxygen release from arterioles ( approximately 55 microm diameter) was measured in the hamster window chamber model during flow and no-flow conditions. Flow was stopped by microvascular transcutaneous occlusion using a glass pipette held by a manipulator. The reduction of the intra-arteriolar oxygen tension (Po2) was measured by the phosphorescence quenching of preinfused Pd-porphyrin, 100 microm downstream from the occlusion. Oxygen release from arterioles was found to be 53% greater during flow than no-flow conditions (2.6 vs. 1.7 x 10(-5) ml O2.cm(-2).s(-1), P < 0.05). Acute hemodilution with dextran 70 was used to reduce vessel oxygen content, significantly increase wall shear stress (14%, P < 0.05), reduce Hct to 28.4% (SD 1.0) [vs. 48.8% (SD 1.8) at baseline], lower oxygen supply by the arterioles (10%, P < 0.05), and increase oxygen release from the arterioles (39%, P < 0.05). Hemodilution also increased microcirculation oxygen extraction (33% greater than nonhemodilution, P < 0.05) and oxygen consumption by the vessel wall, as shown by an increase in vessel wall oxygen gradient [difference in Po2 between the blood and the tissue side of the arteriolar wall, nonhemodiluted 16.2 Torr (SD 1.0) vs. hemodiluted 18.3 Torr (SD 1.4), P < 0.05]. Oxygen released by the arterioles during flow vs. nonflow was increased significantly after hemodilution (3.6 vs. 1.8 x 10(-5) ml O2.cm(-2).s(-1), P < 0.05). The oxygen cost induced by wall shear stress, suggested by our findings, may be >15% of the total oxygen delivery to tissues by arterioles during flow in this preparation.     

Mass transfer limitation of sulfate in methanogenic aggregates

The role of mass transfer limitation of sulfate as a factor governing the competition between sulfate reducing and methane producing bacteria in methanogenic aggregates was theoretically evaluated by the calculation of steady-state sulfate microprofiles using a reference set of parameters obtained from the literature. The shooting method was used as a numerical technique for solving the mathematical model. The effect of the parameters on mass transport limitation was tested by varying each reference value of the parameters with a factor of 3. Sulfate limitation within granules prevailed at moderate (0.1 kg m(-3)) and low sulfate concentrations in the bulk liquid, at high maximum sulfate utilization rates (3.73 x 10(-5) kg SO(4) (2-) kg(-1) VSS S(-1) or biomass concentrations (40 KG VSS m(-3)), and in large aggregates (radius of 7.5 10(-4) m). The effective diffusion coefficient of sulfate and the affinity constant were less determinative for the penetration depth of sulfate within a granule. (c) 1994 John Wiley & Sons, Inc.     

喀斯特峰丛洼地原生林土壤团聚体有机碳的剖面分布

以喀斯特峰丛洼地的伊桐、侧柏和菜豆树3个原生林植物群落为对象,分析了土壤团聚体的组成、有机碳及其剖面分布.结果表明:3个植物群落的土壤分布均以＞2 mm大粒径团聚体为主,约占土壤团聚体总量的76％.土壤总有机碳含量介于12.73 ～ 68.66 g·kg-1之间,群落类型显著影响土壤有机碳含量及其分布.＜1 mm小粒径团聚体中的有机碳含量比＞2 mm团聚体稍高,但大部分土壤有机碳储存在大粒径团聚体中,＞2 mm团聚体对土壤有机碳的贡献率约70％.2 ～5和5～8 mm团聚体含量与土壤有机碳含量呈显著正相关.提高土壤中2～8 mm团聚体的含量能有效增强喀斯特地区土壤固碳能力.伊桐群落2～8 mm土壤团聚体的含量及其全土有机碳含量分别达46％和37.62 g· kg-1,伊桐更适合作为喀斯特地区生态恢复树种.