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

Abstract

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. 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 ndings revealed that the solute-phase concentration of most elements, other than Sb and Cd, increased to a peak after 30 days of paddy soil ooding and then decreased. Additionally, Sb and Cd continuously decreased during ooding. 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.

Sustainable Immobilization of Arsenic by Man-Made Aerenchymatous Tissues in Paddy Soil

“…This aligns with previous reports in the rice rhizosphere. 29,54 The porewater As(III) and As(V) had a significant positive relationship with the arrA gene across the MAT−soil interface, which is likely because the arrA gene plays a crucial role in As mobilization in a reducing environment. 55 In contrast, As(III) showed a significant negative relationship with the aioA gene (Figure 6), supporting the importance of microbially mediated As(III) oxidation in micro-oxic environments in saturated soils.…”

“…The aioA gene mediating As(III) oxidation was observed in this study, which has also been observed in the rhizosphere of many wetland plants. 29,61 The adsorption of As(V) by Fe(III) (oxyhydr)oxides and other soil solids is much higher than that of As(III), 50,62 hence oxidation of As(III) to As(V) will aid in reducing the release of As in soils. This shares a similar mechanism as using active oxidants such as Mn oxides and nitrate to immobilize As in soils.…”

“…Rice ( O . sativa L.) cultivar, Yongyou-15, was sterilized and germinated following a method described in a previous report . The seedlings were grown in a Hoagland culture in a greenhouse and transplanted at the four-leaf stage.…”

“…Rice (O. sativa L.) cultivar, Yongyou-15, was sterilized and germinated following a method described in a previous report. 29 The seedlings were grown in a Hoagland culture in a greenhouse and transplanted at the four-leaf stage. Well-mixed soils (∼5.0 kg) were added into a black plastic pot (length × width × height = 15.5 cm × 15.5 cm × 20.0 cm) with a soil depth of 15 cm.…”

Special issue: Rhizosphere spatiotemporal organisation: an integrated approach linking above and belowground

“…For enzyme activity, reflecting root and/ or microbial activity, a new micro-zymography approach was developed by Ghaderi et al (2022). Yuan et al (2022) presented a new method for in-situ measurements of small-scale, spatially and temporally resolved sampling of soil pore water. For the quantification of exudation, Oburger et al (2022b, this issue) present a rapid and cheap method for determination of C in exudate samples, which can be used for samples obtained from hydroponics or from a soil-hydroponic hybrid approach.…”