Microdistribution of major to trace elements between roots of Halimione portulacoides and host sediments (Tagus estuary marsh, Portugal)
This study presents a micrometre-scale map of the elemental distribution within roots and surrounding sediment of Halimione portulacoides of a contaminated salt marsh in the Tagus estuary.
Microprobe particle induced X-ray emission analysis was performed in sediment slices containing roots with tubular rhizoconcretions attached to host sediments.
Strong concentration gradients were found particularly in the inner part of rhizoconcretions adjacent to the root wall. Local enrichment was observed in sediment interstices with Fe precipitates and other associated elements. A maximum of 55 % of Fe was measured near the concretion–root interface, with a decrease to <5 % in the host sediment. Maximum concentrations of P (3 %), As (1,200 μg g−1) and Zn (3,000 μg g−1) were registered in concretions, one order of magnitude above the values of the host sediment. The elemental concentration profiles across roots showed that the epidermis was an efficient selective barrier to the entrance of elements. Fe and As were retained in the epidermis. The highest Cu and Zn concentrations were also observed in the epidermis. However, the concentrations of Mn, Cu and Zn increased in the inner root.
As and Fe were mostly retained in the concretion, whereas P, Mn, Cu and Zn were mobilised by the root.
KeywordsHalimione portulacoides Rhizoconcretion Rhizosphere Salt marsh sediment Elemental distribution Micro-PIXE
A postdoc grant from “Fundação para a Ciência e a Tecnologia” and the European Social Fund support the work of the first author.
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