Protective effect exerted by soil phosphorus on soybean subjected to arsenic and fluoride

Objetive: Arsenic (As) and fluoride (F) are found in groundwater and soils around the world, causing different problems to crops. Because these elements compete against phosphorus (P) in soils and plants, their relationship is complex. The aim of this work was to study the oxidative stress of soybean plants subjected to different concentrations of As and F, and the effect of P.

Methods: The following 10 treatments were carried out in each of two soils with different P content: three As levels (low 10?mg?As?kg^-1, medium 50?mg?As?kg^?1 and high 100?mg As kg^?1), three F levels (low 160?mg?F?kg^?1, medium 250?mg?F?kg^?1 and high 500?mg?F?kg^?1) and three As?+?F levels (same concentrations), and the control treatment (soil with the background As and F concentrations) Lipid peroxidation, chlorophyll, gluthatione contents and antioxidant enzymes activities were determination.

Results: Increased lipid peroxidation and alterations in glutathione content, catalase, superoxide dismutase and peroxidase activities as well as in chlorophyll content revealed that As causes higher oxidative stress in plants grown in soils with low P content.

Conclusion: Stress parameters in F treatments were less affected. Plants grown in soils enriched with P revealed a decrease in the toxic effects caused by As and F.     

Fractionation and bioaccumulation of copper and zinc in wetland soils of the Niger Delta determined by the oil palm

Abstract

The concentration, mobility, bioavailability, distribution and associations of two essential micronutrient elements (copper and zinc) to the oil palm in wetland soils of the Niger delta region of Nigeria was assessed by means of chemical fractionation analysis. The water soluble and plant available fractions were introduced into the sequential extraction scheme. Also assessed were the bioaccumulation (concentration and distribution) of these metals in the leaves and fruits of the oil palm of various ages found around the soil profiles. Copper was obtained more in the amorphous Fe-oxide fraction (151.05 mg kg^?1), but evenly distributed in the exchangeable component (16.16%) with a maximum value of 126.6 mg kg^?1. The water soluble and plant available fractions had 16.15 and 7.54% distribution of Cu respectively. Zinc had 2.35 and 30.42% distribution in the water soluble and plant available fractions respectively. The lowest mean amount of Cu (1.33 mg kg^?1) was determined in the leaves of palms of ages 15–32 years. Palms greater than 60 years had the highest mean concentration of copper (3.91 mg kg^?1) in the leaves while the endosperm (kernel) of palms between 2 and 10 years had concentration of 9.07 mg kg^?1. The fibrous oily mesocarp had the highest amount (16.78 mg kg^?1) of copper in the older palms (>60 years). Similarly, Zn was dominant in the older palms with a mean concentration of 187.14mg kg^?1 obtained in the endosperm (kernel). The bioaccumulation pattern of both metals by the palms irrespective of age and the fractionation analysis revealed sufficient bioavailable and reserved amounts of Zn and Cu in the wetland soils.     

Effects of phytoremediation and application of organic amendment on the mobility of heavy metals in a polluted soil profile

This research aims to assess the effect of the application of biosolids compost and phytoremediation on the mobility of total and biodisponibles (DTPA) fractions of cadmium, copper, lead, and zinc from different horizons of a superficially contaminated soil. Leaching experiment in soil columns was proposed. Treatments contemplated application of compost biosolid and phytoremediation. Two destructive samplings were performed. Total and DTPA trace metals were identified in each horizon. The overall performance of the various elements in its total and DTPA forms show greater concentration in horizon A and fewer gradients between horizons Bt and BC, thus assuming that the high content of clay in horizon Bt (62.9%) limits its movement through the horizons. In the mobile nutrients, a greater mobility was evidenced in DTPA fractions if compared to Total fractions. In the horizon A, the more mobile metals, such as Zn and Cd, evidenced a greater percentage of DTPA/Total fractions in all treatments. The application of compost with or without plant diminished the mobilization of Zn, Cu, and Cd Total, thus limiting a potential leaching to inferior horizons. However, this effect was not observed in the DTPA fraction.     

Carbohydrates in water-stable aggregates and particle size fractions of forested and cultivated soils in two contrasting tropical ecosystems

Information on changes in storage and loss of soil organic carbon (SOC) when tropical forests are converted to cropland is needed for evaluating soil structural degradation and for selecting appropriate sustainable soil management practices. We evaluated changes in SOC storage of organic carbon and acid-hydrolyzable carbohydrates content of aggregated classes and particle size fractions of adjacent forested and cultivated soils in eight agroecosystems from Ethiopian highlands and Nigerian lowlands. In all agroecosystems, SOC content was two to four times higher in the forested than the cultivated soils. Higher SOC content was found in Ethiopian (20.2–47.3 g.kg^–1) than Nigerian (12.0–24.0 g.kg^–1) forested soils. The magnitude of reduction in SOC and total carbohydrates with cultivation was soil-specific, being generally higher in the sandy than the clayey soils. The smaller aggregate classes (< 1.00 mm) and the sand-sized particles (2000–63 µm) of the forested soils were preferentially enriched in carbohydrates relative to larger aggregates (4.75–1.00 mm). Carbohydrates were more concentrated in the clay-size fraction of the forested than in that of the cultivated soils. Cultivation reduced aggregate stability, increased the proportions of the smaller size aggregates and their associated carbohydrates relative to the forested soils. The susceptibility of the cultivated soils to loss in structural stability reflected this initial aggregation which was greater in the more stable clayey than the fragile sandy soils. The aggregate stability of either the forested or the cultivated soil could not be accounted for by the levels of OC or total carbohydrates in the soil.     

Spatial patterns of P fractions and chemical properties in soils of two native shrub communities in Senegal

Two shrub species (Piliostigma reticulatum (D.C.) Hochst (Caesalpinioideae) and Guiera senegalensis J.F. Gmel (Combretaceae) are commonly found in farmers’ fields at varying densities in semi-arid Senegal and throughout the Sahel where soils have chronically low phosphorus (P) availability. It seems plausible that shrub litter and the rhizospheres could influence P fractions and other chemical soil properties that affect crop productivity. Thus, a study was done at two sites, on the distribution of inorganic and organic soil P pools, organic C levels, and pH in soil beneath and outside the canopies of P. reticulatum and G. senegalensis (0-30 cm depth). Both sites had low total P ranging from 64 mg P kg^?1 to 135 mg P kg^-1, and low extractable PO₄ (resin Pi) (1–6 mg P kg^?1) with P fractions dominated by NaOH-P. Organic P (Po) made up about 50% of total P, and most of the organic P (>60%) was found in the NaOH-P fractions. The labile P, particularly bicarb-Po was higher in soil beneath shrub canopies (8.4 mg P kg ^?1), than outside the canopy (6.2 mg P kg ^?1). Similarly, C, N and P to a lesser extent, were more concentrated beneath shrub canopies. P. reticulatum soil was dominated by the NaOH-Po fraction, whereas G. senegalensis had higher bicarb-Po at one of the study sites. An index of biologically available organic P (Bicarb-Po) / (Bicarb-Po?+?Bicar-Pi?+?Resin Pi) was ?>?60% and indicates that biological processes represent an important part of P cycling in these shrub ecosystems. The differential ability of shrubs in modifying soil chemical properties under their canopies has major implications for biogeochemical cycling of nutrients and C in sandy soils of semi arid Sahelian ecosystems.     

Sulfur in Ghanaian soils

Studies were carried out to examine factors which might influence the distribution of S in Ghanaian soils. Nine soil profiles developed over granitic rocks, three each representing the upper slope (US), middle slope (MS) and lower slope (LS) of catena in the evergreen high rain forest (ERF), semi-deciduous rain forest (SDF) and the interior savanna (ISAV) zone of Ghana were selected. The total S contents varied from 9 to 347 ppm; the average for all the surface and subsurface horizons was 141 ppm and for subsoils 105 ppm. The contents also varied according to: (1) the ecological zone as follows: ERF 0) SDF>ISAV and (2) the topographic position: US>MS>LS. The total S was closely correlated with organic C and total N in the surface and subsurface horizons (r=0.931^*** and 0.941^*** respectively). Inorganic sulfate was generally higher in the subsoils than in the surface and subsurface horizons of the ERF and SDF profiles whereas the opposite was the case in the ISAV profiles. Based on the critical value of 6 ppm in surface soils, all the savanna soils would be considered S deficient.The total organic S, which constituted from 56 to over 95% of the total S in the profiles, was significantly correlated with total N both in the surface and subsurface horizons (N:S ratio=9.1:1) and in the subsoils (N:S ratio=7.6:1). Fractionation of the organic S showed that HI-reducible S ranged from 14 to 117 ppm in the surface and subsurface horizons (average 55 ppm, equivalent to 47% of the total organic S) and from 2 to 169 ppm (average 55 ppm, equivalent to 60% of the total organic S) in the subsoils. The C-bonded S ranged from 6 to 223 ppm (average 73 ppm, equivalent to 57% of the total organic S) in the surface and subsurface horizons and from 1 to 83 ppm (average 29 ppm, equivalent to 32% of the total organic S) in the subsoils. HI-reducible S was significantly correlated with organic C (r=0.805^***) and total N (r=0.845^***) in the surface and subsurface horizons only whereas C-bonded S was significantly correlated with organic C and total N in both the surface and subsurface horizons and subsoils (r=0.870^*** and 0.624^*** respectively).The N:S ratios varied from 6.0 to 12.7 in the surface and subsurface horizons and from 0.5 to 27.3 in the subsoils. However the N:S ratio was less variable within the profile than the C:S ratio. The C:N:S ratios varied considerably within the profile and among the different soils but they fall within the range of values reported world-wide.     

Flue gas desulfurization gypsum improves orchardgrass root density and water extraction in an acid subsoil

In Appalachia, many soils are acidic, high in exchangeable aluminium, and low in calcium. Large amounts of high gypsum flue gas desulfurization (FGD) by-products are currently disposed of into landfills, although they have potential value as a soil amendment for the region. This study was conducted to determine if leaching an acid subsoil with a saturated solution of a FGD by-product can improve the subsoil as a rooting media for orchardgrass (Dactylis glomerata L.) which is widely used for pasture in the region. Orchardgrass was grown in soil from a pHc 3.8 (in 0.01 M CaCl₂) Lily loam Bt horizon (fine loamy siliceous, mesic, Typic Hapludult) leached with two different rates of a saturated FGD by-product aqueous solution, as well as in soil that was limed, and an unamended soil. Water use by a clipped and partially enclosed vegetative canopy was measured in a growth chamber during two drying cycles. Small but consistent increases in water use were correlated with decreases in aluminium saturation of the soil. The effect was greatest during the second drying cycle. Increases in root biomass were also correlated with decreases in aluminium saturation. The effect of treatment on the pattern of water use altered after the first drying cycle when water uptake became most restricted in the unamended treatment. The manganese content of leaf tissue increased from 208 mg kg^-1 to 570 mg kg^-1 between the unaltered and highest leaching rate treatment. The highest level was still below the 2000 mg kg^-1 that is considered toxic to grazing animals. These results suggest that the application of high gypsum FGD by-products to pastures in Appalachia has the potential to improve root growth and functioning in subsoil horizons, but some care may be needed to monitor forage quality.     

Soil Organic Carbon Pools and Stocks in Permafrost-Affected Soils on the Tibetan Plateau

The Tibetan Plateau reacts particularly sensitively to possible effects of climate change. Approximately two thirds of the total area is affected by permafrost. To get a better understanding of the role of permafrost on soil organic carbon pools and stocks, investigations were carried out including both discontinuous (site Huashixia, HUA) and continuous permafrost (site Wudaoliang, WUD). Three organic carbon fractions were isolated using density separation combined with ultrasonic dispersion: the light fractions (<1.6 g cm⁻³) of free particulate organic matter (FPOM) and occluded particulate organic matter (OPOM), plus a heavy fraction (>1.6 g cm⁻³) of mineral associated organic matter (MOM). The fractions were analyzed for C, N, and their portion of organic C. FPOM contained an average SOC content of 252 g kg⁻¹. Higher SOC contents (320 g kg⁻¹) were found in OPOM while MOM had the lowest SOC contents (29 g kg⁻¹). Due to their lower density the easily decomposable fractions FPOM and OPOM contribute 27% (HUA) and 22% (WUD) to the total SOC stocks. In HUA mean SOC stocks (0–30 cm depth) account for 10.4 kg m⁻², compared to 3.4 kg m⁻² in WUD. 53% of the SOC is stored in the upper 10 cm in WUD, in HUA only 39%. Highest POM values of 36% occurred in profiles with high soil moisture content. SOC stocks, soil moisture and active layer thickness correlated strongly in discontinuous permafrost while no correlation between SOC stocks and active layer thickness and only a weak relation between soil moisture and SOC stocks could be found in continuous permafrost. Consequently, permafrost-affected soils in discontinuous permafrost environments are susceptible to soil moisture changes due to alterations in quantity and seasonal distribution of precipitation, increasing temperature and therefore evaporation.     

Vertical distribution of biological and geochemical phosphorus subcycles in two southern Appalachian forest soils

We measured Al, Fe, and P fractions by horizon in two southern Appalachian forest soil profiles, and compared solution PO₄ ^–1 removal in chloroform-sterilized and non-sterilized soils, to determine whether biological and geochemical P subcycles were vertically stratified in these soils. Because organic matter can inhibit Al and Fe oxide crystallization, we hypothesized that concentrations of non-crystalline (oxalate-extractable) Al (Al₀) and Fe (Fe₀), and concomitantly P sorption, would be greatest in near-surface mineral (A) horizons of these soils.Al₀ and Fe₀ reached maximum concentrations in forest floor and near-surface mineral horizons, declined significantly with depth in the mineral soil, and were highly correlated with P sorption capacity. Small pools of readily acid-soluble (AF-extractable) and readily-desorbable P suggested that PO₄ ^3– was tightly bound to Al and Fe hydroxide surfaces. P sorption in CHCl₃-sterilized mineral soils did not differ significantly from P sorption in non-sterilized soils, but CHCl₃ sterilization reduced P sorption 40–80% in the forest floor. CHCl₃ labile (microbial) P also reached maximum concentrations in forest floor and near-surface mineral horizons, comprising 31–35% of forest floor organic P. Combined with previous estimates of plant root distributions, data suggest that biological and geochemical P subcycles are not distinctly vertically stratified in these soils. Plant roots, soil microorganisms, and P sorbing minerals all reach maximum relative concentrations in near-surface mineral horizons, where they are likely to compete strongly for PO₄ ^3– available in solution.     

Arsenic and Mercury in the Soils of an Industrial City in the Donets Basin,Ukraine

Soil and house dust collected in and around Hg mines and a processing facility in Horlivka, a mid-sized city in the Donets Basin of southeastern Ukraine, have elevated As and Hg levels. Surface soils collected at a former Hg-processing facility had up to 1300 mg kg^?1 As and 8800 mg kg^?1 Hg; 1M HCl extractions showed 74–93% of the total As, and 1–13% of the total Hg to be solubilized, suggesting differential environmental mobility between these elements. In general, lower extractability of As and Hg was seen in soil samples up to 12 km from the Hg-processing facility, and the extractable (1M HCl, synthetic precipitation, deionized water) fractions of As are greater than those for Hg, indicating that Hg is present in a more resistant form than As. The means (standard deviation) of total As and Hg in grab samples collected from playgrounds and public spaces within 12 km of the industrial facility were 64 (±38) mg kg^?1 As and 12 (±9.4) mg kg^?1 Hg; all concentrations are elevated compared to regional soils. The mean concentrations of As and Hg in dust from homes in Horlivka were 5–15 times higher than dust from homes in a control city. Estimates of possible exposure to As and Hg through inadvertent soil ingestion are provided.     

Leaf silicon content in banana (Musa spp.) reveals the weathering stage of volcanic ash soils in Guadeloupe

Several plant species accumulate silicon, which is taken up by roots in soil solution. The Si concentration in soil solution can be governed by silicate dissolution and formation, and thus soil constitution. Here, we study the Si leaf content of mature banana plants (Musa acuminata cv Grande Naine) cropped on soils derived from andesitic ash in Guadeloupe through standard foliar analysis. The soils strongly differ in weathering stage and total Si content. The most desilicated soils (Andosol–Nitisol–Ferralsol) occur in the wettest areas, on the Eastern slopes (Es) of the volcano exposed to rain bearing winds. Least weathered soils (Andosol–Cambisol) occur on Western slopes (Ws). The average leaf Si concentration ranges from 2.7 to 3.9 g kg^?1 for bananas cropped in Es soils, and from 7.7 to 9.6 g kg^?1 in Ws soils. The leaf Si concentrations are lowest for the Es gibbsite-rich Andosols and Ferralsols. The leaf Si concentration is positively correlated with soil CaCl₂-extractable Si content, soil Si content and total reserve in weatherable minerals. The silicon content of banana leaves thus reveals the weathering stage of volcanic ash soils in Guadeloupe.     

Persistence and impact on microorganisms of Bacillus thuringiensis proteins in some Zimbabwean soils

The persistence of the Bacillus thuringiensis subsp. kurstaki (Btk) toxin (Cry1Ab protein) from Bt maize (MON810, Yieldgard®) residues incorporated in a vertisol (739 g clay kg^?1) was investigated. The maize residues were incubated in the soil for 4 weeks, and activity of the toxin in the residues was bioassayed using larvae of the diamondback moth, Plutella xylostella (Lepidoptera: Yponomeutidae). Corrected mortality of P. xylostella in the bioassays decreased from 76% to 30% in less than a week of incubation in the soil. In addition to the above observations, the effects of Btk, Bt subsp. israelensis (Bti), and Bt subsp. tenebrionis (Btt) proteins on the soil microbiota were examined using a vertisol, an alfisol, and an oxisol. The pre-incubated soils (7 days after moisture adjustment) were treated with crystal proteins of Btk, Bti, and Btt and incubated for further a 7-day period. Microbial biomass carbon (MBC) and counts of culturable bacteria and fungi were determined. The proteins did not show effects on MBC or bacterial and fungal counts, possibly as a result of adsorption of the proteins on soil particles, which could have rendered the proteins inaccessible for microbial utilization. Microbial biomass carbon and counts arranged in decreasing order were vertisol>oxisol>alfisol, similar to the amounts of organic C and clay in the soils. However, bacteria and fungi counts were higher in the vertisol than in the alfisol and the oxisol soils. Our observations suggest that larvicidal proteins produced by different subspecies of Bt and Bt maize could persist in tropical soils as a result of adsorption on soil clays but that there were no observable effect on the soil microbiota.     

Enhanced mineralization and denitrification as a result of heterogeneous distribution of clover residues in soil

Batch studies were conducted with Mn oxides (birnessite-hausmannite mixture, BHM) and samples of four soil series from the Mid-Atlantic region of the USA to determine effects of reducing organic acids, similar to those found in the rhizosphere, on the SeO₃/SeO₄ distribution. Jackland (Typic Hapludalf), Myersville (Ultic Hapludalf), Christiana (Aeric Paleaquult), and Evesboro (Typic Quartizipsamment) A and B horizon soil samples with and without prior Mn oxide reduction were incubated aerobically for 10 d with 0.1 mmol kg^-1 SeO₃ and 0 or 25 mmol kg^-1 of ascorbic acid, gallic acid, oxalic acid, or citric acid. Selenite was also added to BHM (10 mmol kg^-1) with 0 or 0.1 mmol kg^-1 ascorbic acid. The availability of Se for plant uptake as a result of root-soil interactions was examined using growth chamber studies with barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) seedlings grown in 150-mL cone-shaped containers to maximize root-soil surface interactions and to create rhizosphere soil throughout the root zone. In the BHM system ascorbic acid increased oxidation of SeO₃ to SeO₄ to 33% of added SeO₃. In the presence of ascorbic and gallic acids and Mn oxides, oxidation of SeO₃ to SeO₄ occurred in the B horizons of all the soils and in the A horizons of Jackland and Myersville soils. Removal of Mn oxides decreased the oxidation in some samples. Wheat and barley plants were able to accumulate up to 20 mol Se kg^-1 from the Jackland soil when soluble Se was not measurable. The root-soil interactions in the Jackland soil with barley and wheat provided the plant with Se from insoluble sources. The results also indicate that Mn oxides coming in contact with reducing root exudates have a greater ability to oxidize SeO₃ to SeO₄. Thus, rhizosphere processes play an important role in the availability of Se for plant uptake.Maryland Agricultural Experiment Station Scientific Article A 6381.Maryland Agricultural Experiment Station Scientific Article A 6381.     

Potential use of endophytic root bacteria and host plants to degrade hydrocarbons

Abstract

Microbe-assisted phytoremediation depends on competent root-associated microorganisms that enhance remediation efficiency of organic compounds. Endophytic bacteria are a key element of the root microbiome and may assist plant degradation of contaminants. The aim of this study was to investigate the application of four hydrocarbon-degrading endophytic strains previously isolated from an oil sands reclamation area. Strains EA1-17 (Stenotrophomonas sp.), EA2-30 (Flavobacterium sp.), EA4-40 (Pantoea sp.), and EA6-5 (Pseudomonas sp.) were inoculated in white sweet clover growing on soils amended with diesel at 5,000, 10,000, and 20,000?mg·kg^?1. Our results indicate that plant growth inhibition caused by diesel fuel toxicity was overcome in inoculated plants, which showed significantly higher plant biomass. Analysis of soil F2 and F3 hydrocarbon fractions also revealed that these soils were remediated by inoculated plants when diesel was applied at 10,000?mg·kg^?1 and 20,000?mg·kg^?1. In addition, quantification of hydrocarbon-degrading genes suggests that all bacterial strains successfully colonized sweet clover plants. Overall, the endophytic strain EA6-5 (Pseudomonas sp.), which harbored hydrocarbon-degrading genes, was the most effective candidate in phytoremediation experiments and could be a strategy to increase plant tolerance and hydrocarbon degradation in contaminated (e.g., diesel fuel) soils.     

Thiobacilli and sulphate production from inorganic sulphur compounds in upper horizons of spruce forest soils

The species representation of Thiobacilli was investigated in horizons F, H and A of spruce forest at ten localities. Concentrations of Thiobacilli in the selected localities and ability of the soils to oxidize sulphur compounds to sulphate were determined. Horizons F exhibited a high oxidative activity, a lower activity was found in horizon H and the lowest one was detected in horizon A. The activities showed spring and autumn maxima. Horizons F, H and A contained 10⁴-10⁵, 10²-10³ and 10^l-10³, respectively, Thiobacilli in 1 g dry soil.Thiobacillus thioparus was detected in all three horizons from all localities,T.thiooxidans was found in all horizons F, only in some horizons H and was not detected in horizons A.T.novellus was found only in some samples without any relation to the horizons,T. denitrificans was not detected at all.     

Soil Organic Carbon Content Decreases in Both Surface and Subsoil Mineral Horizons by Simulated Future Increases in Labile Carbon Inputs in a Temperate Coniferous Forest

Soils represent important pools of soil organic carbon (SOC) that can be greatly influenced by labile C inputs, which are expected to increase in future due to CO₂ enrichment of atmosphere and a concomitant rise in plant primary productivity. Studying effects of variable labile C inputs on SOC pool helps to understand how soils respond to global change. However, this knowledge is missing for coniferous forest soils despite being widespread throughout the northern temperate zone. We conducted a 7-month field manipulation experiment to study the effects of variable labile C inputs (simulated by additions of C₄ sucrose) on the C content in soil fractions and on microbial abundance in the organic (O), surface mineral (A), and subsoil mineral (B) horizons of a temperate coniferous forest soil. SOC in less-protected soil fractions and total organic C were substantially decreased by labile C additions that simulated future increases in C inputs. The SOC losses were comparable between the A and B horizon (40% vs. 30%). However, because sucrose availability estimated from its incorporation into soil fractions and microbial biomass sharply decreased with soil depth, the loss of C was higher in the B than in the A horizon when related to the amount of sucrose added. Utilization of sucrose was highest by fungi in the O horizon and by bacteria in the mineral soil horizons. The results indicate that future increases in labile C inputs to coniferous forest soils will cause rapid and substantial losses of SOC in both the surface and subsoil mineral horizons.

     

Sorption of dissolved organic matter by mineral soils of the Siberian forest tundra

Because of low net production in arctic and subarctic surface water, dissolved organic matter (DOM) discharged from terrestrial settings plays an important role for carbon and nitrogen dynamics in arctic aquatic systems. Sorption, typically controlling the export of DOM from soil, may be influenced by the permafrost regime. To confirm the potential sorptive control on the release of DOM from permafrost soils in central northern Siberia, we examined the sorption of DOM by mineral soils of Gelisols and Inceptisols with varying depth of the active layer. Water‐soluble organic matter in the O horizons of the Gelisols was less (338 and 407 mg C kg^?1) and comprised more dissolved organic carbon (DOC) in the hydrophobic fraction (HoDOC) (63% and 70%) than in the O horizons of the Inceptisols (686 and 706 mg C kg^?1, 45% and 48% HoDOC). All A and B horizons from Gelisols sorbed DOC strongly, with a preference for HoDOC. Almost all horizons of the Inceptisols showed a weaker sorption of DOC than those of the Gelisols. The C horizons of the Inceptisols, having a weak overall DOC sorption, sorbed C in the hydrophilic fraction (HiDOC) stronger than HoDOC. The reason for the poor overall sorption and also the preferential sorption of HiDOC is likely the high pH (pH>7.0) of the C horizons and the smaller concentrations of iron oxides. For all soils, the sorption of HoDOC related positively to oxalate‐ and dithionite–citrate‐extractable iron. The A horizons released large amounts of DOC with 46–80% of HiDOC. The released DOC was significantly (r=0.78, P<0.05) correlated with the contents of soil organic carbon. From these results, we assume that large concentrations of DOM comprising large shares of HiDOC can pass mineral soils where the active layer is thin (i.e. in Gelisols), and enter streams. Soils with deep active layer (i.e. Inceptisols), may release little DOM because of more frequent infiltration of DOM into their thick mineral horizons despite their smaller contents of reactive, poorly crystalline minerals. The results obtained for the Inceptisols are in agreement with the situation observed for streams connecting to Yenisei at lower latitudes than 65°50′ with continuous to discontinuous permafrost. The smaller sorption of DOM by the Gelisols is in agreement with the larger DOM concentrations in more northern catchments. However, the Gelisols preferentially retained the HoDOC which dominates the DOC in streams towards north. This discrepancy can be explained by additional seepage water from the organic horizons that is discharged into streams without intensive contact with the mineral soil.     

Biosorption of scandium and yttrium from solutions

Summary The usage of biosorbents allows separation of scandium and yttrium from each other and from Fe, Al, Ti, Si, and Ca in hydrometallurgical processing of ores and wastes. It was shown that sorption of scandium and yttrium increased with the increase in pH of solution. Initial rate of scandium sorption depended on the biomass type; however 85–98% of scandium was sorbed within 10–30 min with most biomass types tested. The presence of aluminum, iron (III), and titanium in the solution inhibited sorption of scandium and particularly yttrium. After four cycles of sorption, 98.8% of scandium and 87% of yttrium was extracted from red mud leach solution by the biomass of Saccharomyces cerevisiae and Aspergillus terreus, respectively. Selectivity of the process of scandium and yttrium recovery could be achieved during sorption and also desorption, when solubilization of sorbed associated elements was inhibited by high pH values.     

Characterizing cultivable soil microbial communities from copper fungicide-amended olive orchard and vineyard soils

Use of copper-based fungicides has led to an increase in the total Cu content in agriculture soils. The focus of this study was to determine fractionation of Cu and to investigate the structure and the diversity of cultivable bacterial communities in two vineyards (one 25 years old and one 2 years old), one olive orchard and two forest soils. All soils developed on an Oligocene sandstone. The concentration of total Cu in the old vineyard (176.6 mg kg⁻¹) and olive orchard (145.5–296.7 mg kg⁻¹) was from 5 to 10 times higher than in forest soils. The major amount of Cu was found bound to the humic substances in cultivated soils, whereas in forest soils Cu was found in the residual mineral fraction. A relationship was found between the number of cultivable Cu-tolerant bacteria and total Cu content in soil. In the cultivated soils, Cu had a toxicological effect on bacterial community, and thereby Cu-levels > to 145 mg kg⁻¹ could be a risk to soil biota. Microbial communities were analysed by community level physiological profiling (CLPP), using the Biolog system, and by the amplified ribosomal DNA restriction analysis (ARDRA) approach. Only when cell suspensions containing 10⁴ colony-forming units (c.f.u.) were inoculated in each well of Biolog EcoPlates it was possible to discriminate microbial communities from different soil samples. As expected, 16S ARDRA showed that cultivated soils had a lower microbial diversity in respect to forest soils.     

Distribution and bioavailability of heavy metals in different particle-size fractions of sediments in Taihu Lake,China

Abstract

Taihu Lake is one of the most important water sources in the economically developed central-eastern part of China, and metal pollution is a major concern for the lake. The distribution and bioavailability of Cd, Cr, Cu, Pb, Sb and Zn were analysed in undifferentiated bottom sediments and in various particle-size fractions of the sediment from different parts of the lake. The average concentration of total metals in undifferentiated sediments ranged from 0.86 mg kg^-1 (Cd) to 95.45 mg kg^-1 (Zn) for the entire lake, with the highest concentrations in Zhushan Bay. The concentration of heavy metals was higher in extremely fine sands (0.064–0.125 mm) and fine sands (0.125–0.25 mm) than in other fractions. Sequential extractions showed that Cu, Zn and Cd were the most bioavailable accounting for 55.6%, 38.7% and 30.0% of their total concentration, respectively. However, the bioavailable proportion of many metals was not significantly different between grain grades except for Cu and Zn, which were higher in silts (<0.064 mm) than in other grades. Compared with the background values of local soils, the concentration of Zn, Cd, Cu, Pb and Sb was higher, indicating enrichment in the sediment. From ecological safety concerns, Zn, Cd and Cu should be examined closely because of their higher bioavailabilty in the sediment.