Controlling factors of iron plaque formation and its adsorption of cadmium and arsenic throughout the entire life cycle of rice plants

Abstract

Iron (Fe) plaque, which forms on the surface of rice roots, plays a crucial role in immobilizing heavy metal(loids), thus reducing their accumulation in rice plants. However, the principal factors influencing Fe plaque formation and its adsorption capacity for heavy metal(loid)s throughout the rice plant's lifecycle remain poorly understood. Thus, this study investigated the dynamics of Fe plaque formation and its ability to adsorb cadmium (Cd) and arsenic (As) across different growth stages, aiming to identify the key drivers behind these processes. The findings reveal that the rate of radial oxygen loss (ROL) and the abundance of plaque-associated microbes are the primary drivers of Fe plaque formation, with their relative importance ranging from 1.4 % to 81 %. Similarly, the adsorption of As by Fe plaque is principally determined by the rate of ROL and the quantity of Fe plaque, with subsequent effects from the total Fe in rhizospheric soil, arsenate-reducing bacteria, and organic matter-degrading bacteria. The relative importance of these factors ranges from 6.0 % to 11.7 %. By contrast, the adsorption of Cd onto Fe plaque is primarily affected by competition for adsorption sites with ammonium in soils and the presence of organic matter-degrading bacteria, contributing 25.5 % and 23.5 % to the adsorption process, respectively. These findings provide significant insights into the development of Fe plaque and its absorption of heavy metal(loid)s throughout the lifecycle of rice plants.