Metal Availability and Chemical Properties in the Rhizosphere of Lupinus albus L. Growing in a High-Metal Calcareous Soil

Abstract

Chemical processes in the rhizosphere play a major role in the availability of metals to plants. The objective of this study was to assess the potential of white lupin (Lupinus albus L.) for the phytoimmobilisation of heavy metals in a calcareous soil with high levels of Zn and Pb (2,058 and 2,947 μg g −1 , respectively) by evaluating the chemical changes in the rhizosphere, relative to bulk soil, which modify the solubility of heavy metals. Plants were cultivated for 74 days in specially designed pots (rhizopots) in which rhizosphere was sampled easily under controlled conditions. White lupin accumulated high concentrations of Mn in the shoots (average of 4,960 μg g −1 ), well above the normal concentration in plants (300 μg g −1 ). But the metal concentrations found in shoots were not at toxic levels. Rhizosphere soil showed a significantly greater redox potential (245 mV) and water-soluble organic carbon content (34.6 μg C g −1 ) than bulk soil (227 mV; 27.6 μg C g −1 ). Root activity decreased EDTA-extractable Pb, Zn and Fe and promoted their precipitation as insoluble compounds in the residual fraction (acid digestion), hardly available to plants. These results indicate the suitability of this annual N 2 -fixing species for the initial phytoimmobilisation of heavy metals in contaminated soils.

Phytoextraction of heavy metal polluted soils using Sedum plumbizincicola inoculated with metal mobilizing Phyllobacterium myrsinacearum RC6b

“…However, Jeong et al (2012) found that the inoculation of plants with P-solubilizing Bacillus megaterium increased the Cd concentration in B. juncea and Abutilon theophrasti by two folds compared with respective non-inoculated control. Taken together, present and previous research indicating that besides the bacterial metal solubilization activity, the other factors including soil nutrients level, pH, type of metals, plants, etc., greatly influence the metal solubilization in soils and thereby alter its uptake by plants (Martínez-Alcalá et al, 2009;Rajkumar et al, 2013).…”

Concentrations of Available Heavy Metals in Mediterranean Agricultural Soils and their Relation with Some Soil Selected Properties: A Case Study in Typical Mediterranean Soils

“…In Portugal and Spain for instance, there is hardly any information at all on available heavy metals in agricultural soils, and this lack of information is reflected in poorly informed legislation, which does not take soil characteristics into account [17,18]. The initial soil pH and the ability of plant roots to change the pH have been found to be the principal predictors of the exchange of heavy metals, and therefore of their bioavailability [19]. It is generally accepted that anthropogenic heavy metal contamination exists mainly in the form of reactive species on the soil surface, and the concepts of "bioavailability" and "bio-accessibility" were introduced to express the actual effect of the concentration of a contaminant on organisms in the ecosystem [16,[20][21][22].…”

Ancient Heavy Metal Contamination in Soils as a Driver of Tolerant Anthyllis vulneraria Rhizobial Communities

“…However, some reports found that with long-term contamination, metals such as zinc (Zn) and cadmium (Cd) did not decrease rhizobial diversity (23) or rhizobial numbers (24). The effects that metals have on microbial diversity and composition (25) depend upon the metal availability, which is influenced by other factors such as climate (26), soil type and structure (27,28), presence of organic matter (29), pH (30), and plant roots (31).…”