es501127k_si_001.pdf (368.89 kB)
Localized Flux Maxima of Arsenic, Lead, and Iron around Root Apices in Flooded Lowland Rice
journal contribution
posted on 2015-12-17, 04:16 authored by Paul N. Williams, Jakob Santner, Morten Larsen, Niklas
J. Lehto, Eva Oburger, Walter Wenzel, Ronnie N. Glud, William Davison, Hao ZhangIn
wetland-adapted plants, such as rice, it is typically root apexes,
sites of rapid entry for water/nutrients, where radial oxygen losses
(ROLs) are highest. Nutrient/toxic metal uptake therefore largely
occurs through oxidized zones and pH microgradients. However, the
processes controlling the acquisition of trace elements in rice have
been difficult to explore experimentally because of a lack of techniques
for simultaneously measuring labile trace elements and O2/pH. Here, we use new diffusive gradients in thin films (DGT)/planar
optode sandwich sensors deployed in situ on rice
roots to demonstrate a new geochemical niche of greatly enhanced As,
Pb, and Fe(II) mobilization into solution immediately adjacent to
the root tips characterized by O2 enrichment and low pH.
Fe(II) mobilization was congruent to that of the peripheral edge of
the aerobic root zone, demonstrating that the Fe(II) mobilization
maximum only developed in a narrow O2 range as the oxidation
front penetrates the reducing soil. The Fe flux to the DGT resin at
the root apexes was 3-fold higher than the anaerobic bulk soil and
27 times greater than the aerobic rooting zone. These results provide
new evidence for the importance of coupled diffusion and oxidation
of Fe in modulating trace metal solubilization, dispersion, and plant
uptake.