Comparison between fractionation and bioavailability of trace elements in rhizosphere and bulk soils

Abstract

Rhizosphere is a microbiosphere and has quite different chemical, physical and biological properties from bulk soils. A greenhouse experiment was performed to compare the difference of fractionation and bioavailability of trace elements Cr, Ni, Zn, Cu, Pb and Cd between rhizosphere soil and bulk soil. In the meantime, the influence of air-drying on the fractionation and bioavailability was also investigated by using wet soil sample as a control. Soils in a homemade rhizobox were divided into four zones: rhizosphere, near rhizosphere, near bulk soil and bulk soil zones, which was designated as S 1 , S 2 , S 3 and S 4 . Elemental speciations were fractionated to water soluble, exchangeable and carbonate bound (B1), Fe-Mn oxide bound (B2), and organic and sulfide bound (B3) by a sequential extraction procedure. Speciation differences were observed for elements Cr, Ni, Zn, Cu, Pb and Cd between the rhizosphere and bulk soils, and between the air-dried and wet soils as well. The concentrations of all six heavy metals in fraction B1 followed the order of S 2 > S 3 > S 1 > S 4 and for B2, the order was S 2 > S 3 % S 4 > S 1 . For B3, the order was S 1 > S 3 % S 4 > S 2 , while for Cd the order was S 2 > S 3 % S 4 > S 1 . The air-drying increased elemental concentration in fractions B1 and B2 by 20-50% and decreased in fraction B3 by about 20-100%. Correlation analysis also indicated that the bioavailability correlation coefficient of fraction B1 in rhizosphere wet soil to plants was better than that between either air-dried or nonrhizosphere soils. Therefore, application of rhizosphere wet soils should be recommended in the future study on the speciation analysis of trace elements in soils and bioavailability. Ó

Rhizosphere Concentrations of Zinc and Cadmium in a Metal Contaminated Soil After Repeated Phytoextraction BySedum Plumbizincicola

“…The properties of the rhizosphere are different from those of bulk soil in terms of a range of biochemical, chemical and physical processes that occur as a consequence of root growth, water and nutrient uptake, respiration and rhizodeposition (Wang et al 2002;Hinsinger et al 2005). Field data support the hypothesis that exudation of organic ligands may contribute to enhanced solubility and replenishment of metals in the rhizosphere of hyperaccumulating species (Wenzel et al 2003).…”

Copper release kinetics: Effect of two extractants and wheat (Triticum aestivum L.) rhizosphere

“…Means in final row for amounts of Cu release in each extractant from the bulk and the rhizosphere soil followed by the different letters are significantly different (P < 0.01); DTPA-TEA -diethylenetriaminepentaacetic acid-triethanolamine Table 4. Coefficient of determination (R 2 ) and standard error of the estimate (SE, mg/kg) of various kinetic models for Cu release in diethylenetriaminepentaacetic acid-triethanolamine (DTPA-TEA) and citric acid (2003) and Wang et al (2002), the different chemical and biological conditions of the rhizosphere soil can change Cu fractions and therefore amounts of release of Cu. The best supporting evidence for any equation used to describe the kinetics of Cu release is the comparison of the amount of Cu desorption with plant indices on soils with a range of Cu supply.…”

“…In this study, a homemade rhizobox (Wang et al 2002) was used to plant wheat. The rhizobox was divided into three sections: a central zone or rhizosphere zone (30 mm in length), which was surrounded by nylon cloth (300 mesh), and left and right non-rhizosphere zones (bulk soils) (50 mm in length).…”

“…Plants have the ability to transform metal fractions for easier uptake through root exudation or pH changes in the rhizosphere (Wang et al 2002). The soil properties, metal fractions, plant species and especially soil-plant interactions determine the bioavailability of metals in soils.…”

Role of Trichoderma and Sinorhizobium Strains for Improving Growth and Nutritional Status of Alfalfa under Cd Stress

“…The rhizosphere also affects the availability of heavy metals. Early studies have indicated that there is higher concentration of exchangeable and carbonate bound Cr, Ni, Zn, Cu, Pb and Cd in the rhizosphere than in bulk soil (Wang et al, 2002). Root -induced changes in the rhizosphere are important factors controlling nutrient dynamics in this zone and thus the mineral nutrition of plants.…”