Distinct and Dynamic Distributions of Multiple Elements and Their Species in the Rice Rhizosphere

Abstract

AimsThe biogeochemical cycles of elements from soils to plants are mainly governed by their rhizosphere processes. Understanding these processes is challenging and remains largely unresolved due to the complex interrelationships among different elements and due to a lack of appropriate techniques for simultaneous spatiotemporal monitoring.MethodsThis study employed an In-situ Porewater Iterative (IPI) sampler array (0-22 mm measurement distance every 1.7 mm, with a time interval of 3 to 10 days) to capture the in situ spatiotemporal dynamics of ten elements (Fe, Mn, As, P, S, Cr, Co, Zn, Sb and Cd) in the paddy rhizosphere to examine their covarying changes in time and space dimensions.ResultsThe findings revealed that the solute-phase concentration of most elements, other than Sb and Cd, increased to a peak after 30 days of paddy soil flooding and then decreased. Additionally, Sb and Cd continuously decreased during flooding. Fe (-52%), Mn (-17%), P (-43%), Co (-11%), and As species (-74%) were substantially immobilized within a 10 mm zone around the roots, while Zn (28%) and Cd (41%) increased. The greater immobilization of As and re-mobilization of Cd, in the rhizosphere, are stimulated by biotic oxidation of arsenite to arsenate with root oxygen loss and the pH decrease, respectively.ConclusionsOur study showed most sampled elements covaried with Fe both in time and space in the rhizosphere, but the elements are temporally and spatially determined by multiple biogeochemical processes in soils as well as exudates from plant roots.