Analysis of nickel concentration profiles around the roots of the hyperaccumulator plant Berkheya coddii using MRI and numerical simulations

Abstract

Abstract Investigations of soil-root interactions are
hampered by the difficult experimental accessibility of
the rhizosphere. Here we show the potential of Magnetic
Resonance Imaging (MRI) as a non-destructive measurement
technique in combination with numerical
modelling to study the dynamics of the spatial distribution
of dissolved nickel (Ni2+) around the roots of the
nickel hyperaccumulator plant Berkheya coddii. Special
rhizoboxes were used in which a root monolayer
had been grown, separated from an adjacent inert glass
bead packing by a nylon membrane. After applying a
Ni2+ solution of 10 mg l−1, the rhizobox was imaged
repeatedly using MRI. The obtained temporal sequence
of 2-dimensional Ni2+ maps in the vicinity of
the roots showed that Ni2+ concentrations increased
towards the root plane, revealing an accumulation
pattern. Numerical modelling supported the Ni2+
distributions to result from advective water flow
towards the root plane, driven by transpiration, and
diffusion of Ni2+ tending to eliminate the concentration
gradient. With the model, we could study how the
accumulation pattern of Ni2+ in the root zone transforms
into a depletion pattern depending on transpiration
rate, solute uptake rate, and Ni2+ concentration in
solution.