Distinct and dynamic distributions of multiple elements and their species in the rice rhizosphere

Aims: The 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. Methods: This study employed an updated In-situ Porewater Iterative (IPI) sampler to collect porewater across the rice rhizosphere at a spatial resolution of 1.7 mm and a time interval of 3–10 days. An IPI sampler array (0–22 mm measurement distance every 1.7 mm) was adopted 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, with an emphasis on As and Cd. Results: The 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. Almost all arsenite-oxidizing genes were significantly promoted in the rhizosphere. Conclusions: Our 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.