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1.
Abstract

Zinc (Zn) speciation was determined in a Zn pre‐treated Andosol, Inceptisol, and a Vertisol before and after adding phosphate. The fractions obtained, i.e., soluble, exchangeable, iron‐manganese (Fe‐Mn) bound, chelated and insoluble organic forms had a different distribution in the three soils. The exchangeable form predominated in the Andosol, followed by Fe‐Mn oxide bound Zn and minor amounts of the chelated forms, whereas Fe‐Mn oxide bound Zn was very abundant in the Inceptisol and Vertisol. Sizable amounts of the exchangeable form were also present. Phosphate pre‐treatment of the Inceptisol and Vertisol did not alter the distribution of the different forms of Zn, whereas in the Andosol the exchangeable as well as the Fe‐Mn oxide bound Zn increased markedly, chelated Zn also increased somewhat.  相似文献   

2.
Greenhouse experiment was conducted to assess the iron (Fe) and zinc (Zn) fractionation patterns in soils of arbuscular mycorrhizal (AM) fungus-inoculated and uninoculated maize plants fertilized with varying levels of Fe and Zn. Soil samples were collected for Fe and Zn fractions and available Fe, Zn and phosphorus (P) contents besides organic and biomass carbon (BMC), soil enzymes and glomalin. Major portion of Fe and Zn fractionations was found to occur in the residual form. Mycorrhizal symbiosis increased the organically bound forms of Fe and Zn while reducing the crystalline oxide, residual Fe and Zn fractions, indicating the transformation of unavailable forms into available forms. Soil enzymes, viz. dehydrogenase and acid phosphatase activities in M+ soils, were significantly higher than M? soil consistently. Overall, the data suggest that mycorrhizal symbiosis enhanced the availability of Fe and Zn as a result of preferential fractionation and biochemical changes that may alleviate micronutrient deficiencies in calcareous soil.

Abbreviations: AM: arbuscular mycorrhiza; Fe: Iron; Zn: Zinc; P: Phosphorous; Amox-Zn: amorphous oxide bound zinc; Cryox-Zn: crystalline oxide bound zinc; DAS: days after sowing; DTPA: diethylene Triamine Penta Acetic Acid; MnO2-Zn: manganese oxide bound zinc; OC-Zn: organically bound zinc; WSEX: water soluble plus exchangeable zinc; MnO2 Fe: manganese oxide bound iron; OC-Fe: Organically bound iron; WSEX Fe: water soluble plus exchangeable iron.  相似文献   

3.
Information on soil zinc (Zn) distribution is essential for understanding its chemical reactions and bioavailability. An experiment was conducted to evaluate the effect of wheat straw, cow manure, and vermicompost applied with Zn rates on Zn distribution in a calcareous soil. A sequential extraction scheme was used to fractionate Zn into soluble and exchangeable, bound to carbonate, organically bound, bound to manganese (Mn) oxide, bound to amorphous iron (Fe) oxide, bound to crystalline Fe oxide, and residual forms. In untreated soil, Zn was mainly in the residual fraction. Increasing rates of applied Zn increased all forms of Zn. Carbonate and residual forms showed the greatest increase. Organic materials application increased all fractions, except Mn-oxide form, and this increase was more pronounced for the organically bound form. Concentration of soluble, exchangeable, and organically bound forms was greatest in cow manure–amended samples as compared to other organic materials, suggesting that cow manure contained more bioavailable Zn than other organic materials.  相似文献   

4.
An experiment was conducted to evaluate the effect of zinc (Zn) rates and vermicompost levels on distribution of Zn forms of a calcareous soil. After incubation periods, soil samples were air dried, and a sequential extraction scheme was used to fractionate Zn into soluble and exchangeable, bound to carbonate, organically bound, bound to manganese (Mn) oxide, bound to amorphous iron (Fe) oxide, bound to crystalline Fe oxide, and residual forms. In untreated soil, Zn was mainly in the residual fraction. Increasing rates of applied Zn significantly increased all forms of Zn. Carbonate and residual forms showed the greatest increase. Application of vermicompost significantly increased all fractions except Mn-oxide form. This increase was more pronounced for organically bound, soluble, and exchangeable forms, indicating an increase in bioavailability of soil Zn. Incubation time significantly decreased soluble, exchangeable, and organically bound forms but increased other forms of Zn, meaning a significant reduction in Zn phytoavailability in soil with time.  相似文献   

5.
The association of Al, Mn, Fe, Ba, Zn, Cr, Ni, Co and Pb withsoil organic matter (SOM) was investigated in three Japanesesoils. Organically bound metals were assayed by elementalanalysis of a fraction extracted with acidified hydrogenperoxide (H2O2) and the humic acid extracted withalkaline reagent, from soil sampled at various depths of solums.A Dystric Cambisol showed higher extractability with acidifiedH2O2 for most of the metals than a Humic Andosol and an Orthic Acrisol. A Humic Andosol had more metals associated with humicacid than the other two soils.Cu showed high extractability with acidified H2O2 andalso significant association with humic acid, while Pb showedhigh extractability with acidified H2O2 but itsassociation with humic acid was relatively low among the metalsinvestigated. As humic acid is highly resistant to weathering,retention of Cu with SOM may last longer than that of Pb.The binding of metals with SOM probably has contributed to theaccumulation of some metals in organic-rich shallow horizons of soil. Such metals were Zn, Cu, Ni and Pb in a Dystric Cambisol,Cu in a Humic Andosol, and Pb and Cu in an Orthic Arisol.  相似文献   

6.
本文对甘肃省主要农业土壤中Ｃｕ、Ｚｎ、Ｍｎ、Ｆｅ的形态及其有效性进行了研究。结果表明，供试土壤的全Ｃｕ含量范围为２２－２４ｍｇ／ｋｇ，全Ｍｎ为５４２－７７２ｍｇ／ｋｇ，全Ｆｅ为３５６８５－３８３５５ｍｇ／ｋｇ。四种元素均以灌漠土的含量最低，褐土最高。土壤中Ｃｕ、Ｚｎ、Ｍｎ、Ｆｅ的大部分以残留矿物态和氧化铁结合态存在。生物试验和统计分析表明，Ｃｕ、Ｚｎ、Ｍｎ、Ｆｅ的交换态和松结有机态对植物最为有效，  相似文献   

7.
Electron microprobe studies on soil samples with varying heavy metal contamination. 2. Contents of heavy metals and other elements in aggregations of humic substances, litter residues and charcoal particles EMA point analysis show that the organic matter constituents of heavy metal contaminated soils are highly enriched with heavy metals. The maximal trace element accumulation were for Cu up to 13,000 mg/kg, for Zn up to 48,000 mg/kg, for Cd up to 2,100 mg/kg and for Pb up to 193,000 mg/kg. The affinity for the accumulation of the different heavy metals in aggregations of humic substances can be described by the sequence Cu > Pb ? Cd > Zn ? Ni > Co. In very strongly acidified humic top soil horizons the Pb and Cd accumulation in the organic matter constituents is in competition with the accumulation in Fe and Mn oxides. The heavy metal contents (especially of Cu) of the organic matter are often correlated with the content of organically bound calcium. The EMA results also show that high heavy metal amounts occur in combination with Ca-accumulations in the epidermis and the outer bark parenchym of decayed roots. EMA point analysis of the interior of fungus sclerotias show that sclerotias can contain high amounts of heavy metals, in particular lead (up to 49,700 mg Pb/kg). From statistical results of EMA point analysis follows that lead and other heavy metals attached to humic substances are not only bound as metal organic complexes but also as organic metal phosphate complexes. Also charcoal particles of polluted soils contain high amounts of heay metals. The accumulation affinity is quite similar to that of humic substances.  相似文献   

8.
田秀平  李玉梅 《土壤》2009,41(2):196-200
在三江平原上,测定 42 个小区中玉米、大豆、小麦籽实 Fe、Mn、Cu 和 Zn 含量和土壤中各形态 Fe、Mn、Cu 和Zn含量.通过相关分析和通径分析,探讨了土壤中各形态Fe、Mn、Cu 和 Zn 的生物有效性,旨在为该地区合理施用微量元素提供科学依据.试验结果表明,玉米、大豆和小麦籽实含 Fe、Mn、Cu 和 Zn 量与土壤中有效态和交换态 Fe、Mn、Cu和Zn含量呈显著或极显著正相关.有机态 Fe、Mn、Cu 和 Zn含量与玉米、大豆和小麦籽实Fe、Mn、Cu 和 Zn含量也有很好的相关关系.交换态对有效态 Fe、Mn、Cu 和 Zn 影响最大,其次是有机质结合态.铁锰氧化物结合态 Fe、Cu 对有效态 Fe、Cu 及碳酸盐结合态 Mn、Zn 对有效态 Mn、Zn 具有一定正效应.而残留态 Fe、Cu 对有效态 Fe、Cu 和铁锰氧化物结合态 Mn 对有效态 Mn 产生负效应.  相似文献   

9.
Abstract

Forms of metals in soils control their availability to plants and animals and affect the environment differently. To evaluate shifts of metal forms as affected by organic amendments, a sequential extraction procedure was used to fractionate calcium (Ca), iron (Fe), magnesium (Mg), manganese (Mn), and zinc (Zn) in two Hawaii soils amended with three organic wastes. The designated forms are water‐soluble, exchangeable, sorbed, organically bound, carbonate, and residual fractions. The soils, a Mollisol (Waimanalo series) and an Ultisol (Paaloa series), were incubated at 25°C±2°C at field capacity with either chicken manure, sewage sludge, or green manure (cowpea leaves) at 0, 5, and 20 Mg#lbha‐1 for one or five months. Organically bound metals decreased with time because of organic matter decomposition. Iron was mostly residual, but water‐soluble Fe also increased in the acid Paaloa soil. Unlike Fe, most forms of Ca and Mg were transformed to the exchangeable form in 5 months. There was no significant change of Mn forms during the 5‐month incubation. Virtually all organically bound Zn shifted to carbonate and residual forms in the neutral Mollisol (pH 6.2), but shifted to carbonate and exchangeable forms in the acid Ultisol (pH 4.5). The solubilities and exchangeabilities of the five metals in the two soils treated with sewage sludge were not significantly different from those treated with cowpea green manure or chicken manure during the 5‐month incubation. The results suggest that the additions of sewage sludge, chicken manure, or cowpea green manure to Hawaii soils at 20 Mg#lbha‐1 do not have environmentally significant impacts in terms of Ca, Mg, Fe, Mn, and Zn. On the other hand, the amendments may decrease Ca and Mg deficiencies in highly weathered, nutrient‐poor soils such as Ultisols and Oxisols of the tropics.  相似文献   

10.
A sequential extraction procedure was used to investigate the influence of long-term phosphate fertilization on the distribution of cadmium throughout the major components of krasnozemic soils in the potato growing district located to the East of Ballarat, Victoria, Australia. The soil fractions investigated consisted of the water soluble, exchangeable, weakly bound to metal oxides, strongly bound to metal oxides, bound to organic material and residual. Other soil parameters, such as pHH2O, pHCaCl2, electrolytical conductivity and total organic material were investigated. The concentrations of Ca, Mg, Fe, Mn and Zn in each soil fraction were also measured. The total concentration of cadmium in the farmed soils had increased from the background level of 100.5 μg/kg to an average of 210 μg/kg. The proportion of cadmium available or potentially available for plant uptake was very low. On average, 89% of the cadmium in the farmed soils had been adsorbed by amorphous metal oxides and organic material, or was associated with silicates, and is therefore unavailable for plant uptake. The metal oxides adsorbed the highest proportion of cadmium.  相似文献   

11.
Co,Ni,Cr and V in 25 typical soils of China were fractionated into exchangeable,carbonate bound (calcareous soils),Mn oxide bound,organically bound,amorphous Fe oxide bound,crystalline Fe oxide bound and residual forms using a seven-step sequential extraction procedure,so as to study the distribution of chemical forms of these metals as well as the effects of soil proiperties on the distribution.The results showed that most of soil Co,Ni,Cr and V were present in residual forms,and the distribution ratio averaged 48.2% for Co,53.0% for Ni,81.5% for Cr and 68.7% for V.The speciation of heavy metals was greatly influenced by soil physico-chemical properties and the chemistry of elements.The results also indicated that the recovery of metal elements by the sequential extraction procedure was satisfactory,with the relative difference between the sum of seven forms and the total content in soils averaging 9.5% for Co,12.8% for Ni,6.6% for Cr and 7.2% for V.  相似文献   

12.
The extractability and slow reactions of copper (Cu) and zinc (Zn) in a weathered savanna soil under Brachiaria decumbens, Digitaria smutsii, and Stylosanthes guianensis pastures were determined in a laboratory incubation study using a sequential extraction to remove operationally defined fractions of the metals, consisting of exchangeable, organically bound, precipitate [occluded in aluminum (Al) and iron (Fe) oxides], and residual metal fractions. The soils from the pasture fields were spiked with 100 mg Cu kg–1 soil and 200 mg Zn kg–1 soil for 24 weeks. Copper and Zn extractable with 1 N potassium nitrate (KNO3) solution decreased exponentially with time but reached a steady state after 2–3 weeks. The concentrations of Cu and Zn exchangeable with potassium (K) were greater in the Digitaria smutsii field soil than Brachiaria decumbens and Stylosanthes guianensis field soils. The exchangeability of added Cu and Zn (indexed Mn+ (exch)) with time was described by a simple exponential decay equation: Mn+ (exch) = αeβt, where α is a constant, β is a coefficient that defines the rate of transformation of added Cu and Zn from the exchangeable to nonexchangeable pools, and t is time. The β values for Cu (0.040–0.076 mg kg–1 d–1) were almost 10 times greater than those of Zn (0.005–0.007 mg kg–1 d–1). Sequential extraction of added Cu and Zn indicated that between 26 and 30% of the total Cu and between 19 and 30% of the total Zn were associated with organic matter. Similarly, between 35 and 38% of total Cu and between 47 and 60% of total Zn were associated with Fe, Al, and manganese (Mn) oxides. The differential capacity of the pasture fields to transform added Cu and Zn from exchangeable and labile form to nonlabile and nonexchangeable form appears to be governed by organic matter (OM), pH, and active Fe ratio in the pasture field soils.  相似文献   

13.
Adamo  Paola  Dudka  S.  Wilson  M. J.  McHardy  W. J. 《Water, air, and soil pollution》2002,137(1-4):95-116
The sequential extraction procedure proposed by the European Commission Measurement and Testing Programme, combined with Scanning Electron Microscopy and Energy Dispersive X-ray Analysis(SEM/EDS), was applied to identify and quantify the chemical andmineralogical forms of Cu, Ni, Fe, Mn, Zn, Pb, Cr and Cd presentin the topsoil from a mining and smelting area near Sudbury (Ontario, Canada). The possible mobility of the chemical forms was also assessed. The metal fractions: (1) soluble and exchangeable, (2) occluded in manganese oxides and in easily reducible iron oxides, (3) organically bound and in form of sulphides, (4) residual mainly present in the mineral lattice structures were separated. Cu and Ni were the major metallic contaminants, occurring in soils in broad ranges of concentrations: Cu 11–1890 and Ni 23–2150 mg kg-1. Cu was uniformly distributed among allthe extracted fractions. Ni was found associated mainly withthe residual forms, accounting for 17–92%, with an averageof 64%, of the total Ni present in the soils. Fe, Mn, Zn,Pb, Cr and Cd, while occurring in most analysed samples innormal soil concentrations, were primarily held in theresidual mineral fraction (on average >50%). The solubleand exchangeable forms made a small contribution (≤8.1%)to the total content of metals extracted. At least 14% ofthe total Cd, Mn and Pb was mobilised from the reducibleforms. The oxidizable fraction assumed mean values higher than10% only for Pb and Zn. Statistical treatment of the experimental data showed significant correlations between totalmetal content of the soils, some soil properties such as pH value, clay and organic matter content, and metal concentrationsin the various fractions. SEM/EDS analysis showed Fe in form ofoxides and sulphides in soils and Cu, Ni, Mn, Zn and Cr in association with iron oxides. Numerous black carbonaceous particles and precipitates of aluminium fluoride salts, observedin the solid residue left after `total’ digestion, were found tocontain Fe, Ni and Cr.  相似文献   

14.
Twenty surface (0–15 cm) samples of acidic soils were analyzed for water soluble (WS), exchangeable (EX), lead displaceable (Pb-disp.), acid soluble (AS), manganese (Mn) oxide occluded (MnOX), organically bound (OB), amorphous Fe oxide occluded (AFeOX), crystalline iron (Fe) oxide occluded (CFeOX) and residual (RES) fractions of Mn, and also for extractable Mn in some common soil extractants: (diethylenetriaminepentaacetic acid (DTPA) (pH 7.3), DTPA (pH 5.3), AB-DTPA (pH 7.6), Mehlich-3 (pH 2.0), Modified Olsen, 0.005 M calcium chloride (CaCl2), 1 M magnesium chloride (MgCl2) and ion exchange resins. The WS-Mn fraction showed a significant and positive correlation with Mn extractable in DTPA (pH 5.3) and AB-DTPA (pH 7.6), while both WS-Mn and EX-Mn fractions correlated significantly and positively with Mn concentration and uptake by maize plants grown in these soils. The AB-DTPA (pH 7.6) and DTPA (pH 5.3) appeared suitable to assess the availability of Mn in acidic soils.  相似文献   

15.
Different forms of manganese (Mn) were investigated, including total, diethylenetriamine penta-acetic acid (DTPA) extractable, soil solution plus exchangeable (Mn), Mn adsorbed onto inorganic sites, Mn bound by organic sites, and Mn adsorbed onto oxide surfaces, from four soil taxonomic orders in northwestern India. The total Mn content was 200–950 mg kg?1, DTPA-extractable Mn content was 0.60–5.80 mg kg?1, soil solution plus exchangeable Mn content was 0.02–0.80 mg kg?1, Mn adsorbed onto inorganic sites was 2.46–90 mg kg?1, and Mc adsorbed onto oxide surfaces was 6.0–225.0 mg kg?1. Irrespective of the different fractions of Mn their content was generally greater in the fine-textured Alfisols and Inceptisols than in coarse-textured Entisols and Aridisols. The proportion of the Mn fractions extracted from the soil was in the order as follows: Adsorbed onto oxide surfaces > adsorbed onto inorganic site > organically bound > DTPA > soil solution + exchangeable. Based on coefficient of correlation, the soil solution plus exchangeable Mn, held onto organic site and oxide surface (amorphous) and DTPA-extractable Mn, increased with increase in organic carbon of the soil. The two forms, adsorbed onto inorganic site (crystalline) and DTPA extractable, along with organic carbon, increased with increase in clay content of the soil. DTPA-Mn and Mn adsorbed onto oxide surfaces and held on organic site decreased with increased with an increase in calcium carbonate and pH. Total Mn was strongly correlated with organic carbon and clay content of soil. Among the forms, Mn held on the organic site, water soluble + exchangeable and adsorbed onto oxide surface were positively correlated with DTPA-extractable Mn. DTPA-extractable Mn seems to be a good index of Mn availability in soils and this form is helpful for correction of Mn deficiency in the soils of the region. The uptake of Mn was greater in fine-textured Inceptisols and Alfisols than in coarse-textured Entisols and Aridisols. Among the different forms only DTPA-extractable Mn was positively correlated with total uptake of Mn. Among soil properties Mn uptake was only significantly affected by pH of the soil.  相似文献   

16.
Abstract

The Zn content in 8 soil chemical fractions was determined for 21 greenhouse soils and for 8 reference (open field) soils from Kochi Prefecture, Japan to investigate the forms of spontaneously accumulated Zn in the greenhouse soils associated with heavy application of fertilizers and manures. Sequential extraction method was applied to every soil and each Zn fraction was designated as exchangeable (Ex-Zn), Pb-displaceable (Pb-Zn), acid soluble (Aci-Zn), Mn oxide-occluded (MnO-Zn), organically bound (OM-Zn), amorphous Fe oxide-occluded (AFeO-Zn), crystalline Fe oxide-occluded (CFeO-Zn), and residual (Res-Zn) fractions. The Zn content of the greenhouse soils was significantly higher than that of the reference soils in every fraction, except for the CFeO-Zn, and Res-Zn fractions. The Pb-Zn, Aci-Zn, and MnO-Zn fractions showed a difference of more than 60% in the total Zn content between the two soil groups. The amounts of Zn extracted in the Pb-Zn, Aci-Zn, MnO-Zn, AFeO-Zn, and CFeO-Zn fractions of the greenhouse soils increased con-comitantly with the accumulation of applied macro-nutrients. These results indicated that the accumulation of Zn in greenhouse soils caused by intensive fertilization had proceeded through specific adsorption onto or occlusion by the oxides and hydroxides of Fe and Mn in soils.  相似文献   

17.
Abstract

The effect of bacterial inoculation of Rhizobium fredii HN01 on the immobilization and speciation of Cu, Zn, and Cd was studied in Red and Cinnamon soil which are typical Chinese soils. The soil was mixed with bacterial suspension for one week followed by an immobilization of each heavy metal for another week. The total binding and fractionation of heavy metals in soils were analyzed. As compared with the control, the retention of total Cu, Zn, and Cd in Red soil increased by 28, 16, and 28%, respectively, in the presence of rhizobia. The amount of exchangeable, NH4OAc-extractable, Mn oxides-bound and organic matter-bound Cu increased by 23–123%. There were significant decrease of exchangeable Cu and marked increases of NH4OAc-extractable and Mn oxide-bound Cu in Cinnamon soil with the presence of rhizobial cells, although no changes for the total retention of Cu were observed. The amount of exchangeable Zn in Red soil-rhizobia composite was 20% greater than that of the no-rhizobia soil. Addition of rhizobia also increased exchangeable Cd and specifically-adsorbed Cd by 25 and 93%, respectively, in Red soil. No considerable differences were found for the total immobilization of Zn and Cd as well as their distribution in various solid fractions of Cinnamon soil in the absence and presence of rhizobial cells. In terms of soil components, it is assumed that bacterial biomass had a relatively less impact on the species of heavy metals bound with Fe oxides. Results suggested that the retention and speciation of heavy metals in soil are governed largely by the interactions of bacteria with various inorganic and organic soil constituents. The data are useful in understanding the impact of microorganisms on the behavior, mobility and transformation of heavy metals in soil environments.  相似文献   

18.
水稻子实对不同形态重金属的累积差异及其影响因素分析   总被引：3，自引：0，他引：3  
在分析成都平原核心区土壤重金属(Cd、Cr、Pb、Cu、Zn)全量、各形态含量及相应点位种植的水稻子实重金属含量的基础上,通过统计分析、空间插值及线性回归方程的模拟,研究了土壤Cd、Cr、Pb、Cu、Zn全量的空间分布状况、各形态重金属含量统计特征,以及水稻子实对重金属各形态的累积差异及其影响因素。结果表明,成都平原水稻土重金属污染较轻,除Cd外,均低于国家土壤环境质量二级标准。土壤中重金属的可交换态含量均较低,Cd主要以铁锰氧化态存在,Cr、Cu、Zn、Pb主要以残渣态存在。水稻子实对5种重金属的累积效应顺序为:Cd>Zn>Cu>Pb>Cr。与水稻重金属累积关系密切的重金属活性形态(可交换态、碳酸盐结合态、铁锰氧化物结合态和有机物结合态)主要有:Cd的碳酸盐结合态、Cr的可交换态、Pb的有机物结合态和Cu的碳酸盐结合态含量;Zn各活性形态对水稻子实含量的影响不明显。土壤理化性质对不同活性形态重金属元素的影响效应各不相同。活性态Cd主要受有机质、pH和容重的影响;活性态Cr与pH、有机质、CEC和容重密切相关;活性态Pb与有机质、容重、中细粉粒、砂粒等均有密切的关系;Cu的活性主要受粘粒、有机质含量的影响;Zn的有效性主要受pH、有机质、砂粒、容重的影响。总的看来,对土壤Cd、Cr、Pb、Cu、Zn各活性形态含量影响效应较强的是有机质、pH、容重,而与土壤吸附性能密切相关的颗粒组成、CEC的影响不甚明显。  相似文献   

19.
The modified Tessier’s sequential extraction procedure and rhizobox cultivation were employed to investigate the distribution of aluminum (Al) fractions in the acidic rhizosphere soil of Masson pine (Pinus massoniana lamb) seedlings. The results showed that the Al in soils was fractionated into five operationally defined fractions. Three sets of soil samples used in the rhizoboxes were collected from the three forest sites in the southeast of China: Sichuan, Zhejian, and Jiangsu. At the end of 100-day cultivation, the rhizosphere Al fractions for the original or bulk soils were in the order of residual > iron-manganese (Fe-Mn) oxides > organic > carbonate > exchangeable. However, in rhizosphere soil, the Al fraction follows the order of residual > organic > Fe-Mn oxides > carbonate > exchangeable. On average, the rhizosphere experienced significant increase in organically bound Al and slight decrease in exchangeable Al contents, but had decreases in contents for the other three Al fractions compared to the nonrhizosphere. The correlation analysis indicated that the Al contents accumulated in roots were significantly and positively correlated with exchangeable Al contents in the rhizosphere, and also characterized by the major portion of organically bound Al, which exhibited a bioavailable transformation of Al fractions. Results indicated that decreases in both redox potential and soil pH, as well as increase in dissolved organic carbon (DOC), were observed in the rhizosphere. Exchangeable Al and organic Al fractions were dependent mainly on soil pH (hydrogen ion concentration) and DOC, accordingly. Decreasing rhizosphere pH from 5.93 to 3.42 accelerated the secretion of organic carbon. These data are helpful for understanding the mobility and bioavailability of Al fractions in the acidic rhizosphere soils of Masson pine.  相似文献   

20.
Abstract

Ryegrass was grown under greenhouse conditions in pots containing two types of calcareous soil. After 8 harvests, the soil was left in the pots for a simulated fallow period, then reseeded with ryegrass, from which 4 further harvests were obtained. The manganese (Mn) content in the soil samples, taken before seeding and after intensive cropping, was fractionated chemically and physically. Although different trends were apparent in the different fractions, ryegrass cropping enhanced the overall mobilization of soil Mn, which easily surpassed the cumulative Mn uptake. The organically bound Mn and clay‐associated Mn fractions released significant amounts of the element, whereas the behavior of exchangeable Mn, Fe‐oxide associated Mn and sand‐associated Mn fractions varied in the two different soils studied. The silt‐associated Mn fractions increased significantly in both soils.  相似文献   

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