病原菌在红壤胶体上的吸附机制研究

研究了pH和KCl离子强度对猪链球菌和大肠杆菌在红壤胶体表面吸附的影响,结合表面物化性质和Derjaguin-Landau-Verwey-Overbeek(DLVO)理论分析互作机制。结果表明,细菌在红壤胶体表面的吸附等温线能较好拟合Freundlich方程(R20.97),猪链球菌在红壤胶体表面吸附的分配系数(Kf)是大肠杆菌的4.5倍～6.1倍,细菌在去有机质胶体表面吸附的Kf值为含有机质胶体的2.4倍～3.2倍。比表面积越大或zeta电位绝对值越小,细菌吸附能力越强,吸附态细菌位于距红壤胶体表面90～100 nm处的次级小能位置。随着体系pH降低(9.0～4.0)或离子强度增大(1～10 mmol L-1),细菌与红壤胶体互作能障降低,细菌吸附量增大,吸附机制符合DLVO理论;而在高离子强度下(50～100 mmol L-1),猪链球菌吸附量降低了3.4%～5.6%,表明除DLVO作用力外,非DLVO作用力如空间位阻排斥和疏水作用对吸附也有贡献。     

In situ ATR-FTIR study on the adhesion of Pseudomonas putida to Red soil colloids

Purpose

Bacterial adhesion to soil particles is fundamentally important in mineral weathering, organic matter degradation, heavy metal transformation, and fate of pollutants. However, the adhesion mechanism between bacteria and soil colloids under continuous flow systems in the natural environments remains unknown.

Materials and methods

The kinetics of Pseudomonas putida cellular adsorption and desorption on Red soil colloid films under controlled flow systems were examined using in situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Derjaguin–Landau–Verwey–Overbeek (DLVO) and non-DLVO interactions were employed to elucidate the cellular adsorption and desorption kinetics.

Results and discussion

In situ ATR-FTIR spectroscopy can be used effectively to investigate the kinetics of bacterial adhesion to a soil colloid deposit. Surface proteins may be involved in the bacterial adhesion to soil colloids. The adsorption followed pseudo-first-order kinetic equation. High adsorption rate constant and great saturation coverage of adsorbed bacteria were found at high ionic strengths in dynamic systems.

Conclusions

P. putida bacterial cellular adsorption on the soil colloid deposit was irreversible in a wide range of ionic strengths under controlled flow systems. The less reversible adhesion was probably attributed to the DLVO predicted deep secondary energy minima together with non-DLVO factors including polymer bridging, local charge heterogeneities, surface roughness, and Lewis acid–base interactions.     

Effects of soil pH and salt on N2O production in adjacent forest and grassland soils in central Alberta, Canada

Purpose

The effects of soil pH manipulation and KCl addition on N₂O production in adjacent forest and grassland soils in central Alberta were studied in a 16-day laboratory incubation experiment.

Materials and methods

The soils were subjected to four pH and two salt treatments: CK (control)—no addition of acid or alkali solution (pH 4.50 and 4.48 for the forest and grassland soils, respectively; same below); HCl—addition of HCl solution to lower soil pH (3.95 and 3.75); L-KOH and H-KOH—addition of 6 mL of 0.2 (5.36 and 5.57) and 0.4 (6.41 and 6.72)?mol?L^?1 KOH solution, respectively, to increase soil pH to two different levels. In order to differentiate between the effect of a change in pH and of changed salt concentrations on N₂O production, 6 mL of 0.2 (L-KCl) (4.56 and 4.41) or 0.4 mol?L^?1 (H-KCl) (4.59 and 4.42) KCl solutions were also applied as treatments to create two levels of salt application rates.

Results and discussion

Increasing pH promoted gross nitrification and cumulative N₂O production in both soils, particularly in the forest soil. However, cumulative N₂O production decreased in the forest soil but increased in the grassland soil when pH decreased. Cumulative N₂O production in the grassland soil was 36 times higher in the L-KCl treatment (1,442 μg?N?kg^?1) than in the CK (40 μg?N?kg^?1), whereas the H-KCl treatment reduced cumulative N₂O production. In contrast, in the forest soil, both KCl treatments reduced cumulative N₂O production.

Conclusions

(1) The most important factor to increase N₂O production in this study was increasing soil pH, suggesting that careful soil pH management could be used as a tool to control soil N₂O production; (2) salt effect was also involved in affecting N₂O production.     

Evolution and phosphorus fractionation in saline Spolic Technosols flooded with eutrophic water

Purpose

The aim of this study was to evaluate the behaviour of P in saline Spolic Technosols flooded with eutrophic water, with and without plant rhizosphere, in order to assess the role of these soils as sinks or sources of this nutrient.

Materials and methods

Samples were taken from basic (pH?~7.8), carbonated and acidic (pH?~6.2), de-carbonated soils of salt marshes polluted by mine wastes. Three treatments were assayed: pots with Sarcocornia fruticosa, pots with Phragmites australis and pots without plants (bare soil). The pots were flooded for 15?weeks with eutrophic water (PO ₄ ^3? ~6.92?mg?L^?1) and pH, Eh and water-soluble organic carbon and PO ₄ ^3? concentrations were monitored in the soil solution. A soil P fractionation was applied before and after the flooding period.

Results and discussion

The PO ₄ ^3? concentration in the soil solution decreased rapidly in both soils, with and without plant, being diminished by 80?C90?% after 3?h of flooding. The Fe/Mn/Al oxides and the Ca/Mg compounds played an important role in soil P retention. In pots with S. fruticosa, the reductive conditions due to flooding induced P release from metal oxides and P retention to Ca/Mg compounds. In turn, P. australis may have favoured the release of P from carbonates, which was transferred to Fe/Mn/Al compounds.

Conclusions

The retention of P by the soil was the main mechanism involved in the removal of PO ₄ ^3? from the eutrophic flooding water but to evaluate the capacity of these systems as long-term P sinks, the combined effect of metals, Ca/Mg compounds and specific plant species should be considered.     

Adsorption of Phosphate from Aqueous Solution Using an Iron–Zirconium Binary Oxide Sorbent

In this study, an iron?Czirconium binary oxide with a molar ratio of 4:1 was synthesized by a simple coprecipitation process for removal of phosphate from water. The effects of contact time, initial concentration of phosphate solution, temperature, pH of solution, and ionic strength on the efficiency of phosphate removal were investigated. The adsorption data fitted well to the Langmuir model with the maximum P adsorption capacity estimated of 24.9?mg P/g at pH?8.5 and 33.4?mg P/g at pH?5.5. The phosphate adsorption was pH dependent, decreasing with an increase in pH value. The presence of Cl^?, SO ₄ ^2? , and CO ₃ ^2? had little adverse effect on phosphate removal. A desorbability of approximately 53?% was observed with 0.5?M NaOH, indicating a relatively strong bonding between the adsorbed PO ₄ ^3? and the sorptive sites on the surface of the adsorbent. The phosphate uptake was mainly achieved through the replacement of surface hydroxyl groups by the phosphate species and formation of inner-sphere surface complexes at the water/oxide interface. Due to its relatively high adsorption capacity, high selectivity and low cost, this Fe?CZr binary oxide is a very promising candidate for the removal of phosphate ions from wastewater.     

Hydroxyl release by maize (Zea mays L.) roots under acidic conditions due to nitrate absorption and its potential to ameliorate an acidic Ultisol

Purpose

Hydroxyl ion release by maize (Zea mays L.) roots under acidic conditions was investigated with a view to develop a bioremediation method for ameliorating acid soils in tropical and subtropical regions.

Materials and methods

Two hydroponic culture experiments and one pot experiment were conducted: pH, nitrogen state, and rhizobox condition, which investigated the effects of different nitrogen forms on hydroxyl release by maize roots under acidic conditions.

Results and discussion

The pH of the culture solution increased as culture time rose. The gradient of change increased with rising NO₃ ^?/NH₄ ⁺ molar ratios. Maize roots released more hydroxyl ions at pH 4.0 than at pH 5.0. The amount of hydroxyl ions released by maize roots at a constant pH was greater than those at a nonconstant pH. Application of calcium nitrate reduced exchangeable acidity and increased the pH in an Ultisol rhizosphere, compared with bulk soil. The increasing magnitude of soil pH was greater at higher doses of N. The absorption of NO₃ ^?–N increased as the NO₃ ^?/NH₄ ⁺ molar ratios rose, which was responsible for hydroxyl ion release and pH increases in culture solutions and rhizosphere.

Conclusions

Root-induced alkalization in the rhizosphere resulting from nitrate absorption by maize plants can be used to ameliorate acidic Ultisols.     

土壤胶体在不同饱和度土壤介质中的释放与淋溶行为研究

采用饱和与非饱和填充土柱纵向淋溶研究方法,结合对流弥散模型方程（CDE）对穿透曲线的拟合计算,全面考察了土壤介质水饱和度、土壤水pH/离子强度、土壤孔隙水流速和土壤胶体颗粒大小对天然土壤胶体在实际土壤介质中释放、沉积迁移行为的影响。分别获取胶体扩散系数和阻滞因子值,定量说明实验中水化学、水动力学等条件的作用影响力。结果显示,介质不饱和条件不利于胶体的释放和淋溶;高pH和低离子强度条件对土壤胶体释放与迁移有利;淋溶过程的间断干扰,可以促使土壤胶体的增量淋溶释放;淋溶强度及胶体颗粒粒径大小,能够影响胶体穿透时间和穿透浓度峰值大小。     

Estimating Be-7 association with soil particle size fractions for erosion and deposition modelling

Purpose

Estimates of beryllium-7 (⁷Be) enrichment in soil particle size fractions are important for correction in existing soil redistribution models. Little attention has been given to documenting methods of estimating ⁷Be enrichment and assessing differences in enrichment between soil types in the context of soil redistribution modelling. Here, we detail a method for estimating ⁷Be enrichment and correcting soil redistribution estimates.

Materials and methods

Beryllium from a solution of BeCl₂ was adsorbed to two soils with contrasting texture using a batch procedure. Soil fractions were separated by settling according to Stokes’ Law, and samples of bulk and settled fractions were digested and analysed for Be concentration and for specific surface area.

Results and discussion

Both soils demonstrated increasing enrichment of Be with increasing specific surface area. There was a marked difference in enrichment between the soil types with the coarse soil showing greater enrichment in the finer fractions. Calculated enrichment ratios for the coarse soil more than doubled between subfractions of the <63 μm class. Failure to account for the selective transport of fractions during soil redistribution studies could incur substantial errors in soil erosion estimates.

Conclusions

Stable Be provides a practical means of estimating ⁷Be enrichment in soil and subsequent corrections can be incorporated into the conversion model where it is proposed that corrections should be applied to the inventory deficit at each eroding point. The marked difference in enrichment between soil types in these experiments suggested that characterising enrichment and associated correction factors should be done on a site-specific basis. Implementation of the particle size correction procedures requires additional field and laboratory data to standard application of the established soil erosion conversion model.     

恒电荷土壤胶体对Cu2+ 、Pb2+ 的静电吸附与专性吸附特征

供试土壤胶体对Cu2 、Pb2 的吸附强度用pH50 值表示 ,其大小次序为 :土 >黄绵土、黑垆土 >黄褐土。离子强度实验和表面络合反应机制证明恒电荷土壤胶体对Cu2 、Pb2 的吸附含有专性吸附 ,n值可作为判断专性吸附与静电吸附比例的特征值 ,低pH值时 ,以水解 -络合吸附为主 ;高pH值时 ,以水解 -络合与沉淀吸附为主。静电吸附和专性吸附的比例与pH有关 ,各土壤胶体专性吸附百分数大小为 :黄褐土 >土 >黑垆土 >黄绵土。不同土壤胶体在同一介质中对Cu2 、Pb2 的固有络合常数logKintM 值及固有络合ΔG m 负值大小次序与吸附强度大小一致。在定pH定浓条件下 ,考虑离子之间的相互作用时 ,土壤胶体对重金属离子的吸附过程可用BDM等温式描述。供试土壤胶体对Cu2 、Pb2 专性吸附ΔG m 的大小与固有络合ΔG m 接近且大小次序也一致。     

A new model for cation exchange equilibrium considering the electrostatic field of charged particles

Purpose

The aim of this study was to establish a new equilibrium model for cation exchange that quantitatively describe the three important effects: (1) the effect of electrostatic field around soil particles on exchange adsorption; (2) the effect of ionic interaction energy on Boltzmann distribution of cations; and (3) the effect of hydration radius of cation species on cationic distribution between adsorption phase and solution phase.

Materials and methods

In this paper, the Li/Na, Li/K and K/Na exchange were studied theoretically and experimentally. Purified montmorillonite was used as the experimental material and it was H-saturated in advance. In experimental study, approximately 2.5?g of the H-saturated sample was weighed in each experiment, then LiOH/NaOH, LiOH/KOH or KOH/NaOH mixture solution was added. In each experiment, the suspension was allowed to equilibrate for 48?h with continuous shaking at 298?K in an incubator shaker, and then 1?mol/l HCl was used to adjust pH to pH?=?7 when equilibrium was reached. Finally, the suspension was centrifuged and the concentration and of Li⁺, Na⁺ or K⁺ in supernatant was determined.

Results and discussion

In theoretical study, firstly, considering the ionic interaction energy in bulk solution, a modified Poisson?CBoltzmann equation was obtained; secondly, considering the electrostatic field around soil particles, the relationship between the selectivity coefficient and surface potential of particles was established; and thirdly, the modification factors were introduced to modify the effective charge of two cation species that involved in exchange because of the difference in hydration radius. Finally, the new models for describing cation exchange equilibrium were developed. Both theoretical and experimental results showed that the electrostatic field, the ionic interaction energy and the difference in hydration radius of two cation species strongly influenced cation distribution or cation exchange equilibrium. The results indicated that the effective charge could be obtained through either experimental determination or theoretical calculation, and the theoretically predicted values met the experimental results well. Therefore, the ion exchange selectivity series of different cation species with the same valence could be evaluated quantitatively.

Conclusions

New equilibrium models for describing cation exchange were established, for which the three important effects was quantitatively taken into account: the electrostatic field on exchange adsorption, the ionic interaction energy on Boltzmann distribution and the hydration radius of cation species. Both theoretical analyses and experimental results demonstrated that the cation hydration radius and the ionic interaction energy strongly influenced the exchange equilibrium considering the electrostatic field of charged particles.     

电解质阴离子和pH对可变电荷土壤硫酸盐吸附的影响

The effects of three electrolyte anions, ionic strength and pH on the adsorption of sulfate by two variable charge soils, with different surface charge properties were studied. Under the conditions of the same pH and ionic strength the effect of electrolyte anions on the adsorption of sulfate was in the order of Cl^- > NO₃^- > ClO₄^-, indicating the difference of the nature among these three anions. For Ferralsol in the same concentration of chloride and perchloride solutions, the two sulfate adsorption-pH curves could intersect at certain pH value. When pH was higher than the intersecting point, more sulfate was adsorbed in the perchloride solution, while when it was lower than the intersecting point, more sulfate was adsorbed in the chloride solution. In different concentrations of electrolyte solution, the curves of the amount of oxy-acid anion adsorbed, which changed with pH, could intersect at a certain pH, which is termed point of zero salt effect (PZSE) on adsorption. The nature of electrolyte anions influenced obviously the appearance of PZSE for sulfate adsorption. For ferralsol the curves of adsorption converged to about pH 7 in NaCl solution seemed to intersect in NaNO₃ solution and to have a typical PZSE for sulfate adsorption in NaClO₄ solution. For Acrisol the three curves of adsorption were nearly parallel in NaCl and NaNO₃ solutions and converged to pH 6.5 in NaClO₄ solution.     

Nickel adsorption in two Oxisols and an Alfisol as affected by pH,nature of the electrolyte,and ionic strength of soil solution

Background, aim, and scope  The retention of potentially toxic metals in highly weathered soils can follow different pathways that variably affect their mobility and availability in the soil–water–plant system. This study aimed to evaluate the effects of pH, nature of electrolyte, and ionic strength of the solution on nickel (Ni) adsorption by two acric Oxisols and a less weathered Alfisol. Materials and methods  The effect of pH on Ni adsorption was evaluated in surface and subsurface samples from a clayey textured Anionic ‘Rhodic’ Acrudox (RA), a sandy-clayey textured Anionic ‘Xantic’ Acrudox (XA), and a heavy clayey textured Rhodic Kandiudalf (RK). All soil samples were equilibrated with the same concentration of Ni solution (5.0 mg L⁻¹) and two electrolyte solutions (CaCl₂ or NaCl) with different ionic strengths (IS) (1.0, 0.1 and 0.01 mol L⁻¹). The pH of each sample set varied from 3 to 10 in order to obtain sorption envelopes. Results and discussion  Ni adsorption increased as the pH increased, reaching its maximum of nearly pH 6. The adsorption was highest in Alfisol, followed by RA and XA. Competition between Ni²⁺ and Ca²⁺ was higher than that between Ni²⁺ and Na⁺ in all soil samples, as shown by the higher percentage of Ni adsorption at pH 5. At pH values below the intersection point of the three ionic strength curves (zero point of salt effect), Ni adsorption was generally higher in the more concentrated solution (highest IS), probably due to the neutralization of positive charges of soil colloids by Cl⁻ ions and consequent adsorption of Ni²⁺. Above this point, Ni adsorption was higher in the more diluted solution (lowest ionic strength), due to the higher negative potential at the colloid surfaces and the lower ionic competition for exchange sites in soil colloids. Conclusions  The effect of ionic strength was lower in the Oxisols than in the Alfisol. The main mechanism that controlled Ni adsorption in the soils was the ionic exchange, since the adsorption of ionic species varied according to the variation of pH values. The ionic competition revealed the importance of electrolyte composition and ionic strength on Ni adsorption in soils from the humid tropics. Recommendations and perspectives  The presence of NaCl or CaCl₂ in different ionic strengths affects the availability of heavy metals in contaminated soils. Therefore, the study of heavy metal dynamics in highly weathered soils must consider this behavior, especially in soils with large amounts of acric components.     

Impact of organic matter addition on pH change of paddy soils

Purpose

The objective of the present study was to explore the effect of initial pH on the decomposition rate of plant residues and the effect of residue type on soil pH change in three different paddy soils.

Materials and methods

Two variable charge paddy soils (Psammaquent soil and Plinthudult soil) and one constant charge paddy soil (Paleudalfs soil) were used to be incubated at 45 % of field capacity for 105 days at 25 °C in the dark after three plant residues (Chinese milk vetch, wheat straw, and rice straw) were separately added at a level of 12 g?kg^?1 soil. Soil pH, CO₂ escaped, DOC, DON, MBC, MBN, NH ₄ ⁺ , and NO ₃ ^? during the incubation period were dynamically determined.

Results and discussion

Addition of the residues increased soil pH by 0.1–0.8 U, and pH reached a maximum in the Psammaquent and Plinthudult soils with low initial pH at day 105 but at day 3 in the Paleudalfs soil with high initial pH. Incorporation of Chinese milk vetch which had higher concentration of alkalinity (excess cations) and nitrogen increased soil pH more as compared with incorporation of rice and wheat straws. Microbial activity was the highest in Chinese milk vetch treatment, which resulted in the highest increase of soil pH as compared with addition of rice and wheat straws. However, nitrification seemed to be inhibited in the variable charge soils of Psammaquent and Plinthudult but not in the constant charge soil of Paleudalfs.

Conclusions

The effectiveness of increasing soil pH after incorporation of the plant materials would be longer in low initial pH soils of Psammaquent and Plinthudult than in high initial pH soil of Paleudalfs. In order to achieve the same degree of pH improvement, higher amounts of plant residues should be applied in constant charge soils than in variable charge soils.     

Changes in soil solution composition and pH in urine-affected areas of pasture

Changes in soil solution composition and concentrations of exchangeable cations and mineral N in undisturbed cores of pasture soil were investigated in two experiments following applications of sheep urine to the cores. The major cations applied in the urine were K⁺ and Na⁺, and the major anions were HCO₃^? and Cl^?. Addition of urine increased concentrations of exchangeable K⁺, Na⁺ and NH₄⁺ and measured ionic strength of the soil solution throughout the surface 15 cm of soil, demonstrating that the urine moved through the core by macropore flow immediately following addition. Immediately following urine application the ionic strength in soil solution in the surface 2.5 cm of soil increased from 4–6 MM to 24–41 mM. Hydrolysis of urine-urea was extremely rapid, and in less than 1 d high concentrations of NH₄⁺-N (i.e. 270–370 mg N kg^?1) had accumulated in the surface 0–2.5 cm of the urine patch, and soil pH had risen by over one unit. Nitrification then proceeded and, after approximately 15 d, NO₃^? became the dominant form of mineral N present. During nitrification, soil pH declined and the ionic strength of the soil solution increased substantially with NO₃^? becoming the dominant anion present in solution. There were concomitant increases in the concentrations of Ca²⁺ and, to a lesser extent, Mg²⁺ in the soil solution as NO₃^? concentrations increased. After approximately 30 d, concentrations of exchangeable NO₃^? had risen to 250–330 mg N kg^?1, soil solution NO₃^? concentrations had increased to about 80 mmol, dm^?3, and ionic strength in the soil solution had increased to 130–140 mM. These results demonstrate the dominating effect of N transformations in causing large fluctuations in the pH, ionic composition and ionic strength of the soil solution in the urine patch. It was concluded that nutrient availability in the patch was affected directly by nutrient addition in urine, and also probably indirectly through the fluctuations in soil solution pH and ionic strength that occur.     

Evaluating the fraction of electrically associated cations on surfaces of soil particles by extrapolation of strong-field Wien effect measurements in dilute suspensions

Purpose

For agricultural production and environment protection, it is cations loosely bound to the soil particles that have a great significance in short-term processes of adsorption–desorption, exchange, and transport. It is beneficial to be able to evaluate the fractions of these cations in order to correctly predict potential pollution of soils by heavy metals and availability of plant nutrients.

Materials and methods

The homionic suspensions of yellow-brown soil (YB) and black soil I (BI) saturated with Na⁺ and Ca²⁺ and three subsamples of black soil II (BII) saturated with Ca²⁺ and Cd²⁺ were prepared to determine the electrical conductivity (EC) of the suspensions. On the basis of electrical conductivity vs. field strength (EC-E) curve, the fraction of electrically associated cations on surfaces of soil particles was evaluated by extrapolation of strong-field Wien effect measurements in dilute suspensions.

Results and discussion

The maximum dissociation degree (α _max) of Na⁺ adsorbed on surfaces of yellow-brown soil and black soil I was about 0.21, which is approximately twice as much as those of Ca²⁺ (0.07–0.10) adsorbed on surfaces of two soils. The soil type was not the main factor in evaluating α _max, and the valence of the cations was. For divalent cations, α _max of Ca²⁺ and Cd²⁺ adsorbed on soil particles with different contents of organic matter descended in the order: top black soil II?>?bottom black soil II?>?OM-free bottom black soil II.

Conclusions

The relatively small fractions of electrically adsorbed cations—about 0.2 for Na⁺ and 0.1 for Ca²⁺ on yellow-brown and black soils particles indicated that even for the more loosely adsorbed Na⁺ ions, most of the cations in the double layers of soil particles were adsorbed strongly by other, more specific mechanisms and cannot be stripped off into the solution, which would increase its electrical conductivity in a strong applied field.

     

Effects of changes in pH, ionic strength, and sulphate concentration on the CEC of temperate acid forest soils

As the acidity of rain diminishes, changes in the pH, ionic strength, and ion activities of the soil solution will influence the charge characteristics of soil. We have investigated the response of cation exchange capacity (CEC) of three acid forest soils of variable charge to small changes in pH, ionic strength, and SO^2?₄ concentration. The variable charge for these temperate soils has the same significance as for tropical soils and those from volcanic ash. Maximum absolute increase in CEC on increasing pH by 0·2–0·5 units reached 5 cmol_c kg^-1 in O horizons. The increase in CEC on doubling ionic strength in EA and Bsh horizons of a Cambic Podzol was about half that amount, but relative gains compared to effective CEC were 65 and 46%, respectively. For other soil horizons, absolute changes were smaller, and relative changes were between 10 and 30%. Halving the SO^2?₄ concentration significantly influenced CEC only in some samples. Both pH and ionic strength must be adjusted with care when determining CEC_c of acid forest soils. Decreasing acid deposition will not inevitably increase CEC_c because in some soils pH effects may be balanced by simultaneous decrease in ionic strength.     

Spatial distribution of the abundance and activity of the sulfate ester-hydrolyzing microbial community in a rape field

Purpose

Sulfur (S) plays a vital role in plant metabolism, and the detrimental impact of S deficiency in several field crops has increased over the last 30?years. The bio-availability of organic S to plant depends on arylsulfatase (ARS), a key enzyme for S mineralization in soil. In this study, we characterized the spatial variability of ARS activity in an agricultural soil cropped with the rape plant (Brassica napus). Because rape requires relatively large amounts of S per yield unit compared to most grain crops, it is very sensitive to S deprivation similarly to the other plants of the Brassicaceae family, with consequences for seed quality and yield.

Materials and methods

The spatial variability of (a) ARS activity, (b) the abundance of culturable bacteria possessing the ARS, and (c) soil properties (temperature, soil pH, SO ₄ ^2? -S (sulfate-S) content, labile carbon (C) and nitrogen (N), soil microbial biomass carbon SMB-C, and nitrogen SMB-N) was estimated at 40 sites within a rape field, using a 4?×?5-m sampling grid. Geostatistics were used to model the spatial distribution of the measured variables, and relationships between variables were tested using linear statistical analyses.

Results and discussion

The total ARS activity showed a low variability ranging between 69.0 and 153.1???g?p-nitrophenol?g^?1?dry?soil?h^?1 while the abundance of the culturable ARS community ranged within one order of magnitude. The distribution of both the abundance and activity of the ARS community exhibited spatial dependence in 800?m² agricultural field.

Conclusions

The spatial pattern of ARS activity in the field was correlated with several soil properties, and results suggest that soil pH, labile C and N, and SBM-C/SBM-N ratio were the main parameters linked to the ARS activity rather than the abundance of the culturable ARS bacterial community or the SO ₄ ^2? -S concentration.     

支持电解质浓度对磷酸根在可变电荷土壤表面吸附和解吸的影响

研究了离子强度对2种可变电荷土壤中磷酸根吸附和解吸的影响。结果表明,当pH分别大于3.7和4.0时,红壤和砖红壤对磷酸根的吸附量随离子强度的增加而增加;当pH分别小于3.7和4.0时,红壤和砖红壤对磷酸根的吸附量随离子强度呈相反的变化趋势。电解质主要通过改变离子专性吸附面上的电位来影响磷酸根的吸附。Zeta电位的测定结果表明,当pH大于土壤胶体的等电点(IEP)时,吸附面上电位为负值,且随离子强度增加数值减小,对磷酸根的排斥力减小,土壤表面对磷酸根的吸附量增加;当pH小于IEP时,吸附面上的电位为正值,它随离子强度增加而减小,不利于磷酸根的吸附。解吸实验的结果表明,吸附于可变电荷土壤表面的磷酸根在去离子水中的解吸量高于0.1 mol L-1NaNO3体系中的解吸量。这同样由于电解质浓度对土壤表面吸附面上的电位的影响所致。     

Major controlling factors and prediction models for mercury transfer from soil to carrot

Purpose

Soil-plant transfer models are needed to predict levels of mercury (Hg) in vegetables when evaluating food chain risks of Hg contamination in agricultural soils.

Materials and methods

A total of 21 soils covering a wide range of soil properties were spiked with HgCl₂ to investigate the transfer characteristics of Hg from soil to carrot in a greenhouse experiment. The major controlling factors and prediction models were identified and developed using path analysis and stepwise multiple linear regression analysis.

Results and discussion

Carrot Hg concentration was positively correlated with soil total Hg concentration (R ²?=?0.54, P?<?0.001), and the log-transformation greatly improved the correlation (R ²?=?0.76, P?<?0.001). Acidic soil exhibited the highest bioconcentration factor (BCF) (ratio of Hg concentration in carrot to that in soil), while calcareous soil showed the lowest BCF among the 21 soil types. The significant direct effects of soil total Hg (Hg_soil), pH, and free Al oxide (Al_OX) on the carrot Hg concentration (Hg_carrot) as revealed by path analysis were consistent with the result from stepwise multiple linear regression that yielded a three-term regression model: log [Hg_carrot]?=?0.52log [Hg_soil]???0.06pH???0.64log [Al_OX]???1.05 (R ²?=?0.81, P?<?0.001).

Conclusions

Soil Hg concentration, pH, and Al_OX content were the three most important variables associated with carrot Hg concentration. The extended Freundlich-type function could well describe Hg transfer from soil to carrot.