Rhizosphere processes by the nickel hyperaccumulator Odontarrhena chalcidica suggest Ni mobilization

Background and aimsPlant Ni uptake in aboveground biomass exceeding concentrations of 1000 & mu;g g(-1) in dry weight is defined as Ni hyperaccumulation. Whether hyperaccumulators are capable of mobilizing larger Ni pools than non-accumulators is still debated and rhizosphere processes are still largely unknown. The aim of this study was to investigate rhizosphere processes and possible Ni mobilization by the Ni hyperaccumulator Odontarrhena chalcidica and to test Ni uptake in relation to a soil Ni gradient.MethodsThe Ni hyperaccumulator O. chalcidica was grown in a pot experiment on six soils showing a pseudo-total Ni and labile (DTPA-extractable) Ni gradient and on an additional soil showing high pseudo-total but low labile Ni. Soil pore water was sampled to monitor changes in soil solution ionome, pH, and dissolved organic carbon (DOC) along the experiment.ResultsResults showed that Ni and Fe concentrations, pH as well as DOC concentrations in pore water were significantly increased by O. chalcidica compared to unplanted soils. A positive correlation between Ni in shoots and pseudo-total concentrations and pH in soil was observed, although plant Ni concentrations did not clearly show the same linear pattern with soil available Ni.ConclusionsThis study shows a clear root-induced Ni and Fe mobilization in the rhizosphere of O. chalcidica and suggests a rhizosphere mechanism based on soil alkalinization and exudation of organic ligands. Furthermore, it was demonstrated that soil pH and pseudo-total Ni are better predictors of Ni plant uptake in O. chalcidica than labile soil Ni.

Automated summary

This study investigates rhizosphere processes and Ni mobilization by the Ni hyperaccumulator Odontarrhena chalcidica, and tests Ni uptake in relation to a soil Ni gradient. The results show that O. chalcidica increases Ni and Fe concentrations, pH, and DOC concentrations in soil pore water. It is also shown that soil pH and pseudo-total Ni are better predictors of Ni plant uptake in O. chalcidica than labile soil Ni.