ABSTRACT
In flooded soils, soil-water interface (SWI) and plant rhizosphere are the key zone controlling biogeochemical dynamics. Arsenic (As) species and concentrations vary greatly at micro- to cm-scales along the redox gradient. However, the As pattern in the narrow interfaces is rare described, which is mainly due to the lack of proper techniques. Here, with the newly developed Integrated Porewater Injection (IPI) sampler, which is designed for soil porewater sampling with minimum disturbance to saturated soil environment, we successfully revealed the distribution of arsenate (As(V)) and arsenite (As(III)) across SWI and rice rhizosphere in every 2 mm. The results showed the oxygen in surface water and oxygen loss from rice roots strongly impact the dynamic change of As(III) and As(V). With growing rice, iron and As were linearly decreased across 0–10 mm distance from root surface, coinciding with the formation of redox zone by radial O2 loss from root. The oxidizing zone can retain most of mobile As (40 - 80%) from bulk soils. We present a model of As transport from soil to rice, linking the temporal and spatial dynamic regulation of As in paddy soils.
