Pb<Superscript>2+</Superscript> adsorption on birnessite affected by Zn<Superscript>2+</Superscript> and Mn<Superscript>2+</Superscript> pretreatments

Purpose  

Lead contamination is ubiquitous, and much attention has been paid due to its toxicity. The phyllomanganate birnessite is the most common Mn oxide in soils. The MnO₆ octahedral layers may have significant Mn vacancies in the hexagonal birnessites. Among heavy metal ions, birnessites possess the greatest adsorption affinity and capacity for Pb²⁺. The aim of this study was to understand the relationship between vacant Mn octahedral sites and Pb²⁺ adsorption.     

Effects of Graphene Oxide and/or Cd<Superscript>2+</Superscript> on Seed Germination,Seedling Growth,and Uptake to Cd<Superscript>2+</Superscript> in Solution Culture

With increasing graphene oxide (GO) applications in industry and biomedicine, effects of GO on microorganisms, animals, and human health have been frequently studied; however, direct and indirect effects of GO on plants are seldom concerned. In this study, effects of GO and/or Cd²⁺ on seed germination, seedling growth, and uptake to Cd²⁺ were investigated in solution culture. The results showed that GO could quickly adsorb Cd²⁺ in solution, and the higher the GO concentration was, the lower the residual Cd²⁺ concentration was in solution. Rice seed germination, seminal root length, and bud length decreased with increasing GO and Cd²⁺ concentrations respectively, while the presence of GO could alleviate the inhibitive effects of Cd²⁺ on seminal root and bud growth compared with the single Cd²⁺ treatment. In maize seedling, fresh weights of shoot and root showed similar responses to the presence of Cd²⁺ and/or GO. Compared with the single Cd²⁺ treatment, root Cd concentrations were generally increased by GO in high Cd²⁺ solution (20 mg/L), while were slightly affected by GO in low Cd²⁺ solution (5 mg/L) independent of GO concentrations except for 100 mg/L GO. Shoot Cd concentrations were decreased by low GO (100 mg/L) while were increased by high GO (>?500 mg/L) independent of Cd²⁺ concentrations in solution. Moreover, significant interactive effects of GO and Cd²⁺ on root and shoot Cd concentrations were observed. This study indicates that GO can change the effects of Cd²⁺ on seed germination, seedling growth, and uptake to Cd²⁺ in solution through its adsorption on Cd²⁺.     

Two-stage Batch Adsorber Design: A Time-Dependent Langmuir Model for Adsorption of Pb2+ and Cd2+ onto Modified Kaolinite Clay

The kinetics of the adsorption of Pb²⁺ and Cd²⁺ by sodium tetraborate (NTB)-modified kaolinite clay adsorbent was studied. A one-stage and two-stage optimization of equilibrium data were carried out using the Langmuir and time-dependent Langmuir models, respectively. Increasing temperature was found to increase the pseudo-second order kinetic rate constant and kinetic data for Pb²⁺ adsorption were found to fit well with the pseudo-second order kinetic model (PSOM) while that for Cd²⁺ were found to show very good fit to the modified pseudo-first order kinetic model (MPFOM). Binary solutions of Pb²⁺ and Cd²⁺ reduced the adsorption capacity of the modified adsorbent for either metal ion with increased initial sorption rate due to competition of metal ions for available adsorption sites. The use of NTB-modified kaolinite clay adsorbent reduces by approximately 72.2% and 96.3% the amount of kaolinite clay needed to adsorb Pb²⁺ and Cd²⁺ from wastewater solutions. From the two-stage batch adsorber design study, the minimum operating time to determine a specified amount of Pb²⁺ and Cd²⁺ removal was developed. The two-stage batch adsorption process predicted less than half the minimum contact time to reach equilibrium in the one-stage process for the adsorption of Pb²⁺ and Cd²⁺ by NTB-modified kaolinite clay adsorbent and requires 0.05 times the mass of the adsorbent for the single-stage batch adsorption at the same operating conditions.     

羟基磷灰石对铅锌矿区土壤吸附Zn2+、Cd2+的影响

为探究羟基磷灰石(HAP)对矿区土壤重金属的固化效果,采用吸附试验,研究施加HAP的铅锌矿区土壤对Cd~(2+)、Zn~(2+)的动力学吸附和等温吸附效果。结果表明:土壤对Cd~(2+)、Zn~(2+)的吸附量随Cd~(2+)、Zn~(2+)初始浓度的增加而增加;在酸性条件下,其吸附量随pH上升而上升;准二级动力学方程能很好地描述两者的吸附过程,土壤吸附能力随HAP的添加量增大而增强;在Zn—Cd共存体系中,当初始浓度为20mg/L时,土壤对Zn~(2+)、Cd~(2+)的吸附无明显差异,2种金属离子竞争力度小,随着初始浓度上升,竞争明显,对Zn~(2+)的最大吸附量能达到单一体系中的79%～87%,而Cd~(2+)的最大吸附量只有单一体系中的57%～72%,Zn~(2+)的竞争力优于Cd~(2+),Zn~(2+)对Cd~(2+)吸附产生严重的抑制。综上可知,HAP能提高矿区土壤的吸附性能,在Zn、Cd污染土壤中,更能提升土壤对Zn~(2+)的吸附固持能力。     

Enhanced Adsorption of Metal Ions Onto Polyethyleneimine-Impregnated Palm Shell Activated Carbon: Equilibrium Studies

In this study, palm shell activated carbon was impregnated with polyethyleneimine (PEI) and the effect of impregnation on batch adsorption of Ni²⁺, Cd²⁺or Pb²⁺ as well as the equilibrium behavior of adsorption of metal ions on PEI-impregnated AC were investigated. PEI impregnation evidently increased the single metal adsorption capacities of Ni²⁺ or Cd²⁺except for Pb²⁺, where its adsorption capacities were reduced by 16.67% and 19.55% for initial solution pH of 3 and 5 respectively. This suggested that PEI-impregnated AC could be used for selective separation of Pb²⁺ ions from other metal ions. The adsorption data of all the metal ions on both virgin and PEI-impregnated AC for both initial solution pH of 3 and 5 generally fitted the Langmuir and Redlich-Peterson isotherms considerably better than the Freundlich isotherm.     

KINETICS OF ION EXCHANGE IN SOIL ORGANIC MATTER. IV. ADSORPTION AND DESORPTION OF Pb2+, Cu2+, Cd2+, Zn2+ AND Ca2+ BY PEAT

The equilibria as well as the rates of adsorption and desorption of the ions Pb²⁺, Cu²⁺, Cd²⁺, Zn²⁺, and Ca²⁺ by soil organic matter were determined in batch experiments as a function of the amount of metal ions added to an aqueous suspension of HCl-washed peat. Simultaneous determination of the metal ions and hydrogen ions in the solution by atomic absorption spectrophotometry and pH-measurements showed that the adsorption of one divalent metal ion by peat was coupled with the release of two hydrogen ions. Since this equivalent ion-exchange process causes a corresponding increase of the electric conductivity of the solution, the rates of the adsorption and desorption processes were determined by an immersed conductivity electrode. The distribution coefficients show that the selective order for the metal adsorption by peat is Pb²⁺ > Cu²⁺ > Cd²⁺≌ Zn²⁺ > Ca²⁺ in the pH range of 3·5 to 4·5. The slope of -2, as observed in a double logarithmic plot of the distribution coefficients versus the total solution concentration confirms the equivalence of the ion-exchange process of divalent metal ions for monovalent H₃O⁺ -ions in peat. The absolute rates of adsorption, as well as the rates for the fractional attainment of the equilibrium, increase with increasing amounts of metal ions added. This behaviour is also observed for the subsequent desorption of the metal ions by H₃O⁺-ions. At a given amount of metal ions added, the absolute rates of adsorption decrease in the order Pb²⁺ > Cu²⁺ > Cd²⁺ > Zn²⁺ > Ca²⁺, while the rates for the fractional attainment of the equilibrium decrease in the order Ca²⁺ > Zn²⁺≌ Cd²⁺ > Pb²⁺ > Cu²⁺. The half times for adsorption and desorption were in the range of 5 to 15 sec.     

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。     

不同土地利用方式土壤对铜、镉离子的吸附解吸特征

采用一次平衡法对Cu²⁺、Cd²⁺在城市及城郊农田、林地、草地3种土地利用方式土壤中的吸附解吸过程进行比较研究, 结果表明: Cu²⁺、Cd²⁺在3种土地利用方式土壤中的吸附量均随平衡液浓度的增加而增大, Cu²⁺、Cd²⁺在农田土壤上的吸附量均高于林地和草地土壤。分别用Langmuir和Freunlich两种等温吸附方程对吸附过程进行拟合, 3种土壤对Cu²⁺的吸附过程运用Langmuir方程拟合效果好, 而对Cd²⁺的吸附过程运用Freunlich方程拟合效果更好。Cu²⁺在3种土壤的解吸量大小顺序为农田>林地>草地, Cd²⁺在3种土壤的解吸量大小顺序为农田>草地>林地。两种离子在3种土壤中的动态吸附是个快速反应的过程, 随时间延长, 吸附反应趋于平衡。运用双常数函数方程和Elovich方程能较好地拟合重金属在土壤上的吸附动力学过程。Cu²⁺、Cd²⁺的吸附与土壤黏粒含量、有机质含量、CEC和pH均有关。     

添加生物质炭对红壤性水稻土Cd2+吸附解吸特性的影响

为探讨生物质炭对红壤性水稻土中镉(Cd)元素吸附解吸特性的影响,采用一次平衡法研究添加生物质炭后Cd2+在红壤性水稻土中的吸附动力学、等温吸附和解吸过程。结果表明:施用CK(0t/hm^2)、A10(10t/hm^2)、A20(20t/hm^2)、A30(30t/hm^2)和A40(40t/hm^2)生物质炭后,红壤性水稻土对Cd2+的吸附过程是以化学吸附为主、非均匀的多表面吸附。施用CK(0t/hm^2)、A10(10t/h2)、A20(20t/hm^2)、A30(30t/hm^2)和A40(40t/hm^2)生物质炭处理的最大吸附量和最大解吸量分别为2933~3346mg/kg和171~192mg/kg。添加生物质炭可以提高红壤性水稻土对Cd2+的吸附固持能力,同时增强土壤对外源Cd2+的缓冲能力。生物质炭添加量对红壤性水稻土的吸附解吸能力的改良效果具体表现为:A30>A40>A20>A10。高剂量的生物质炭处理使土壤吸附点位饱和,生物质炭吸附能力相对降低。因此,添加30t/hm^2生物质炭是一种有效预防和治理红壤性水稻土镉污染的措施。     

Competitive adsorption and desorption of oxytetracycline and cadmium with different input loadings on cinnamon soil

Purpose

The binary competitive effect could obviously influence the fate and transport behavior of oxytetracycline (OTC) and cadmium (Cd²⁺) in cinnamon soil. However, two pollutants loading into soil usually are different, perhaps because of the three reasons including occurrence of OTC before Cd²⁺, simultaneous occurrence of OTC and Cd²⁺, or occurrence of Cd²⁺ before OTC. The purpose of the study was to predict the competitive adsorption and desorption of OTC and Cd²⁺ as a function of above input loadings on cinnamon soil.

Materials and methods

Adsorption and desorption were determined using the batch equilibrium method in a single or binary system. The Freundlich equation was applied to describe the adsorption/desorption data of OTC and Cd²⁺ in order to obtain adsorption/desorption isotherms for each tested compound and the respective adsorption/desorption coefficients.

Results and discussion

The results indicated that cinnamon soil could strongly adsorb OTC with the adsorption affinity (K _f value) of more than 718 and Cd²⁺ with K _f value of more than 536 in the competitive and non-competitive system, and all adsorption and desorption isotherms of OTC and Cd²⁺ on cinnamon soil were well fitted by the Freundlich equation with r value of more than 0.99 (p?<?0.01). The coexistence of OTC and Cd²⁺ on cinnamon soil promoted significantly Cd²⁺ adsorption when Cd²⁺ firstly or simultaneously occurred on soil, but their coexistence did not affect adsorption of OTC when OTC firstly or simultaneously occurred on soil. Among the three input loadings, the pollutant with later occurring mode had lower K _f and hysteresis coefficient (HI) than the other two input loadings. According to the adsorption intensity parameter (1/n), the presence of Cd²⁺ or OTC with different input loadings could decrease the adsorption intensity of OTC or Cd²⁺ when compared with single occurrence of OTC or Cd²⁺.

Conclusions

The binary competitive effect influenced the adsorption/desorption of OTC and Cd²⁺ differently. The presence of OTC had a stronger influence on the adsorption/desorption of Cd²⁺ than the presence of Cd²⁺ on the adsorption of OTC. The later occurring pollutant on soil had stronger ecological risk than the former occurring pollutant in the binary competitive system. The physical adsorption in the single or binary system could be identified as the dominant mechanisms of OTC and Cd²⁺ adsorption.     

Effect of CO<Subscript>2</Subscript> on nitrification and immobilization of NH<Subscript>4</Subscript><Superscript>+</Superscript>-N

A laboratory incubation experiment was conducted to demonstrate that reduced availability of CO₂ may be an important factor limiting nitrification. Soil samples amended with wheat straw (0%, 0.1% and 0.2%) and (¹⁵NH₄)₂SO₄ (200 mg N kg^–1 soil, 2.213 atom% ¹⁵N excess) were incubated at 30±2°C for 20 days with or without the arrangement for trapping CO₂ resulting from the decomposition of organic matter. Nitrification (as determined by the disappearance of NH₄⁺ and accumulation of NO₃^–) was found to be highly sensitive to available CO₂ decreasing significantly when CO₂ was trapped in alkali solution and increasing substantially when the amount of CO₂ in the soil atmosphere increased due to the decomposition of added wheat straw. The co-efficient of correlation between NH₄⁺-N and NO₃^–-N content of soil was highly significant (r =0.99). During incubation, 0.1–78% of the applied NH₄⁺ was recovered as NO₃^– at different incubation intervals. Amendment of soil with wheat straw significantly increased NH₄⁺ immobilization. From 1.6% to 4.5% of the applied N was unaccounted for and was due to N losses. The results of the study suggest that decreased availability of CO₂ will limit the process of nitrification during soil incubations involving trapping of CO₂ (in closed vessels) or its removal from the stream of air passing over the incubated soil (in open-ended systems).     

Speciation of cadmium,copper, lead,and zinc in contaminated soils

Abstract

To investigate the activity of free cadmium (Cd²⁺), copper (Cu²⁺), lead (Pb²⁺), and zinc (Zn²⁺) ions and analyze their dependence on pH and other soil properties, ten contaminated soils were sampled and analyzed for total contents of Cd, Cu, Pb, and Zn (Cd_T, Cu_T, Pb_T, and Zn_T, respectively), 0.43 MHNO₃‐extractable Cd, Cu, Pb, and Zn (Cd_N, Cu_N, Pb_N, and Zn_N, respectively), pH, dissolved organic matter (DOC), cation exchange capacity (CEC), ammonium oxalate extractable aluminum (Al) and iron (Fe), and dissolved calcium [Ca²⁺]. The activity of free Pb²⁺, Cd²⁺, Cu²⁺, and Zn²⁺ ions in soil solutions was determined using Donnan equilibrium/graphite furnace atomic absorption (DE/GFAA). The solubility of Cd in soils varied from 0.16 to 0.94 μg L^‐1, Cu from 3.43 to 7.42 μg L^‐1, Pb from 1.23 to 5.8 μg L^‐1, and Zn from 24.5 to 34.3 μg L^‐. In saturation soil extracts, the activity of free Cd²⁺ ions constituted 42 to 82% of the dissolved fraction, for Cu²⁺the range was 0.1 to 7.8%, for Pb²⁺ 0.1 to 5.1% and for Zn²⁺2 to 72%. The principal species of Cd, Cu, Pb, and Zn in the soil solution is free metal ions and hydrolyzed ions. Soil pH displayed a pronounced effect on the activity of free Cd²⁺, Cu^2t, Pb²⁺, and Zn²⁺ ions.     

Removal of Pb2+ Ions from Water by Poly(Acrylamide-co-Sodium Methacrylate) Hydrogels

The application of poly(acrylamide-co-sodium methacrylate) (AAm/SMA) hydrogel for the removal of Pb²⁺ ions from aqueous solutions has been investigated using batch adsorption technique. The extent of adsorption was investigated as a function of pH, adsorbent dose, and temperature. The Fourier transform infrared (FTIR) spectra showed that ?CNH₂ and ?CCOOH groups are involved in Pb²⁺ ion adsorption. The obtained results were analyzed by pseudo-first-order, pseudo-second?Corder, and intraparticle diffusion models using both linear and nonlinear methods. It was found that the Pb²⁺ ion adsorption followed pseudo-first-order kinetics. Nonlinear regression analysis of six isotherms, Langmuir, Freundlich, Redlich-Peterson, Toth, Dubinin-Radushkevich, and Sips, have been applied to the sorption data, while the best interpretation was given by Redlich-Peterson. Based on the separation factor, R _L, the Pb²⁺ ion adsorption is favorable, while the negative values of ?G indicates that the Pb²⁺ ion adsorption on the investigated hydrogel is spontaneous.     

Soil N<Subscript>2</Subscript>O emissions and N<Subscript>2</Subscript>O/(N<Subscript>2</Subscript>O+N<Subscript>2</Subscript>) ratio as affected by different fertilization practices and soil moisture

The objective of this work was to evaluate the effect of the chemical nature and application frequency of N fertilizers at different moisture contents on soil N₂O emissions and N₂O/(N₂O+N₂) ratio. The research was based on five fertilization treatments: unfertilized control, a single application of 80 kg ha⁻¹ N-urea, five split applications of 16 kg ha⁻¹ N-urea, a single application of 80 kg ha⁻¹ N–KNO₃, five split applications of 16 kg ha⁻¹ N–KNO₃. Cumulative N₂O emissions for 22 days were unaffected by fertilization treatments at 32% water-filled pore space (WFPS). At 100% and 120% WFPS, cumulative N₂O emissions were highest from soil fertilized with KNO₃. The split application of N fertilizers decreased N₂O emissions compared to a single initial application only when KNO₃ was applied to a saturated soil, at 100% WFPS. Emissions of N₂O were very low after the application of urea, similar to those found at unfertilized soil. Average N₂O/(N₂O+N₂) ratio values were significantly affected by moisture levels (p = 0.015), being the lowest at 120% WFPS. The N₂O/(N₂O+N₂) ratio averaged 0.2 in unfertilized soil and 0.5 in fertilized soil, although these differences were not statistically significant.     

Biotite weathering by <Emphasis Type="Italic">Aspergillus niger</Emphasis> and its potential utilisation

Purpose

Biotite, as a type of associated mineral, is normally applied as a filling material for buildings, or is discarded as tailings. However, as a potassium-bearing phyllosilicate mineral, biotite can be easily weathered by fungi, which leads to its internal potassium being released for agricultural production (1), and the mineral residues being weathered by the fungus may be applied for adsorption of heavy metal ions (2).

Materials and methods

This work investigates the weathering of biotite by Aspergillus niger through the analysis of the differences in ion dissolution from biotite, producing of organic acids, the change of mineral morphology and composition by inductively coupled plasma optical emission spectrometry (ICP-OES), high-performance liquid chromatography (HPLC), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Besides, the mineral residues were applied for adsorption of heavy metal ions.

Results and discussion

Results showed that the mycelia envelope the mineral and form fungal–mineral aggregates. The fungus can secrete a variety of organic acids including citric acid and oxalic acid; these attacked the surface and cleavage of biotite to release ions (Al³⁺, Fe³⁺, Mg²⁺, and K⁺). During incubation with A. niger, biotite weathered as shown by the relative decrease in biotite content and increase in interlayer spacing. Moreover, a certain concentration of phytic acid and tween-80 could promote the release of K⁺, and the fermentation liquid of rice bran has the same effect. Biotite residues showed a good adsorption for Cd²⁺, Pb²⁺, Zn²⁺, and Cu²⁺.

Conclusions

The results indicate that biotite can be biotransformed and release K⁺, of which the production can be acted as heavy metal ion adsorbent. It provides a reference for application of biotite in agriculture and control of heavy metal ion pollution in soil.

     

In situ mineral <Superscript>15</Superscript>N dynamics and fate of added <Superscript>15</Superscript>NH<Subscript>4</Subscript><Superscript>+</Superscript> in hoop pine plantation and adjacent native forest in subtropical Australia

Background, aim, and scope  Hoop pine (Araucaria cunninghamii) is a nitrogen (N) demanding indigenous Australia softwood species with plantations in Southeast Queensland, Australia. Soil fertility has declined with increasing rotations and comparison study of N cycling between hoop pine plantations, and adjacent native forest (NF) is required to develop effective forest management for enhancing sustainable forest production and promoting environmental benefits. Field in situ mineral ¹⁵N transformations in these two forest ecosystems have not been studied. Hence, the present study was to compare the differences in soil nutrients, N transformations, ¹⁵N fluxes, and fate between the hoop pine plantation and the adjacent native forest. Materials and methods  The study sites were in Yarraman State Forest (26°52′ S, 151°51′ E), Southeastern Queensland, Australia. The in situ core incubation method was used in the field experiments. Mineral N was determined using a LACHAT Quickchem Automated Ion Analyzer. ¹⁵N were performed using an isotope ratio mass spectrometer with a Eurovector elemental analyzer. All statistical tests were carried out by the SPSS 11.0 for Windows statistical software package. Results  Soil total C and N were significantly higher in the NF than in the 53-year-old hoop pine plantation. Concentrations of NO₃ ^– were significantly higher in the NF soil than in the plantation soil. The plantation soil had significantly higher ¹⁵N and ¹³C natural abundances than the NF soil. The NF soil had significantly lower C/N ratios than the plantation soil. NO₃ ^––N was dominated in mineral N pools in both NF and plantation soils, accounting for 91.6% and 70.3% of the total mineral N pools, respectively. Rates of net nitrification and net N mineralization were, respectively, four and three times higher in the NF soil than in the plantation soil. The ¹⁵NO₃ ^––N and mineral ¹⁵N were significantly higher in the NF soil than in the plantation soil. Significant difference in ¹⁵NH₄ ⁺–N was found in the NF soil before and after the incubation. Discussion  The NF soil had significantly higher NO₃ ^––N, mineral N, total N and C but lower δ¹⁵N, δ¹³C, and C/N ratios than the plantation soil. Moreover, the rates of soil net N mineralization and nitrification were significantly higher, but ammonification rate was lower in the NF than in the plantation. The NF soil had many more dynamic N transformations than the plantation soil due to the combination of multiple species and layers and, thus, stimulation of microbial activity and alteration of C and N pool sizes in favor of the N transformations by soil microbes. The net rate of N and ¹⁵N transformation demonstrated differences in N dynamic related to the variation in tree species between the two ecosystems. Conclusions  The change of land use and trees species had significant impacts on soil nutrients and N cycling processes. The plantation had larger losses of N than the NF. The NO₃ ^––N and ¹⁵NO₃ ^––N dominated in the mineral N and ¹⁵N pools in both forest ecosystems. Recommendations and perspectives  Native forest soil had strong N dynamic compared with the plantation soil. Composition of multiple tree species with different ecological niches in the plantation could promote the soil ecosystem sustainability. The ¹⁵N isotope dilution technique in the field can be quite useful for studying in situ mineral ¹⁵N transformations and fate to further understand actual N dynamics in natural forest soils.     

有机酸对几种土壤胶体吸附解吸镉离子的影响

用平衡法研究了有机酸对土壤胶体吸附 解吸Cd2 的影响。结果表明 ,黄棕壤、红壤、砖红壤胶体Cd2 最大吸附容量 (Qm)分别为 4 3 7、16 8、1 5 8mmolkg-1。在加入Cd2 浓度相同的条件下 ,土壤胶体Cd2 吸附量随有机酸浓度的升高呈峰形曲线变化。当有机酸与Cd2 共存时 (竞争吸附 ) ,低浓度的草酸 (小于0 5～ 2mmolL-1)或柠檬酸 (小于 0 0 2 5～ 0 2mmolL-1)提高Cd2 吸附量 ,高浓度的草酸或柠檬酸能降低Cd2 吸附量。吸附有机酸后的土壤胶体 (次级吸附 )对Cd2 次级吸附量的影响与竞争吸附一致 ,但两者的Cd2 吸附量变化幅度不一样。这是由于两种吸附体系液相中有机酸残留浓度不同所致。土壤胶体吸附态Cd2 的解吸结果表明 ,草酸浓度不仅影响Cd2 的总解吸量、总解吸率 ,还影响土壤胶体表面KNO3 解吸态与DTPA解吸态Cd2 的分配比例     

Short-term uptake of <Superscript>15</Superscript>NH<Subscript>4</Subscript><Superscript>+</Superscript> into soil microbes and seedlings of pine,spruce and birch in potted soils

Short-term competition between soil microbes and seedlings of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.) and silver birch (Betula pendula Roth) for N was assessed in a pot study using (¹⁵NH₄)₂SO₄ as a tracer. Seedlings were grown in organic and mineral soil, collected from a podsol soil; 3.18 mg (¹⁵NH₄)₂SO₄ per pot were injected into the soil, corresponding to 4 µg ¹⁵N g^-1 d.m. (dry matter) mineral soil and 17 µg ¹⁵N g^-1 d.m. organic soil. The amounts of N and ¹⁵N in the seedlings and in microbial biomass derived from fumigation-extraction were measured 48 h after addition of ¹⁵N. In the mineral soil, 19–30% of the added ¹⁵N was found in the plants and 14–20% in the microbial biomass. There were no statistically significant differences between the tree species. In the organic soil, 74% of the added ¹⁵N was recovered in the microbial biomass in birch soil, compared to 26% and 17% in pine and spruce soils, respectively. Correspondingly, about 70% of the ¹⁵N was recovered in pine and spruce seedlings, and only 23% in birch seedlings. In conclusion, plants generally competed more successfully for added ¹⁵NH₄ ⁺ than soil microbes did. An exception was birch growing in organic soil, where the greater amount of available C from birch root exudates perhaps enabled micro-organisms to utilise more N.     

Effects of successive soil freeze-thaw cycles on soil microbial biomass and organic matter decomposition potential of soils

Abstract

Effects of soil freeze-thaw cycles on soil microbial biomass were examined using 8 soil samples collected from various locations, including 4 arable land sites and 2 forest sites in temperate regions and 2 arable land sites in tropical regions. The amounts of soil microbial biomass C and N, determined by the chloroform fumigation and extraction method, significantly decreased by 6 to 40% following four successive soil freeze-thaw cycles (- 13 and 4°C at 12 h-intervals) compared with the unfrozen control (kept at 4°C during the same period of time as that of the freeze-thaw cycles). In other words, it was suggested that 60 to 94% of the soil microorganisms might survive following the successive freeze-thaw cycles. Canonical correlation analysis revealed a significantly positive correlation between the rate of microbial survival and organic matter content of soil (r = 0.948*). Correlation analysis showed that the microbial survival rate was also positively correlated with the pore-space whose size ranged from 9.5 to 6.0 μm (capillary-equivalent-diameter; r = 0.995**), pH(KCI) values (r = 0.925**), EC values (r = 0.855*), and pH (H₂O) values (r = 0.778*), respectively. These results suggested that the soil physicochemical properties regulating the amount of unfrozen water in soil may affect the rate of microbial survival following the soil freeze-thaw cycles. The potential of organic matter decomposition of the soils was examined to estimate the effects of the soil freeze-thaw cycles on the soil processes associated with the soil microbial communities. The soil freeze-thaw cycles led to significant 6% increase in chitin decomposition and 7% decrease in rice straw decomposition (p < 0.05), suggesting that the partial sterilization associated with the soil freeze-thaw cycles might disturb the soil microbial functions.     

Heavy Metal Uptake by Rape

Abstract

In pot experiments, the effect of single and combined pollution of soil by lead (Pb), cadmium (Cd), and zinc (Zn) and uptake of heavy metals in Brassica napus L. were investigated. There were two main factors that affected the assimilation of Pb, Cd, and Zn by rape: (i) level of soil pollution by the particular element and (ii) the combined influence of Pb, Cd, and Zn. In general, with the increase of the concentrations of Pb, Cd, and Zn in the soil, there were increases in the concentrations of those elements in the roots, stems, and seeds. The main part of the Pb and Zn amounts taken up by the roots from the soil are fixed and accumulated in the roots, and small amounts of them move through the conductive system to the seeds. Cadmium moves relatively easily from root to stem and is accumulated in higher concentrations in the top of the plant.

There is a well‐expressed synergistic interaction between Pb²⁺ and Cd²⁺, as well as of Cd²⁺ and Zn²⁺. Zinc has a highly depressing effect on the assimilation of Cd²⁺, as does Pb²⁺ on the assimilation of Zn²⁺. The combined pollution by Pb, Cd, and Zn stimulated the assimilation of these elements by the roots and foliage and eliminated the effect of Zn²⁺ on Cd²⁺ and of Pb²⁺ on Zn²⁺.