A novel layered culture device reveals spatial dynamics of root element uptake and optimal silicon application site for mitigating chromium uptake by rice.

Understanding root uptake mechanisms for various elements is crucial for optimizing heavy metal remediation strategies and enhancing plant-nutrient interactions. However, simple and effective methods to differentiate the contributions of specific root segments in element uptake are lacking. Here, we developed a layered culture device consisting of a culture box and a plant suspension mechanism, which isolates different root segments through solid media and waterproof coating. Then, we used the device to investigate the roles of distinct root segments (0-1 cm and 1-2 cm from the tip) in heavy metal chromium (Cr) and beneficial element silicon (Si) uptake in rice. The results indicated that the 0-1 cm root segment contributed approximately 58% of leaf Cr(VI), with higher efflux compared to the 1-2 cm segment. Conversely, the 1-2 cm root segment served as the primary source of leaf Si and Cr(III), accounting for 62% and 54%, respectively. The translocation factors for Cr(VI) were similar for both segments (0.039 and 0.032), while the Cr(III) translocation factor for the 0-1 cm root segment (0.061) was 2.8 times that of the 1-2 cm segment. Notably, Si application to the 0-1 cm segment most effectively alleviated Cr (III) and Cr (VI) stress, boosting shoot length, fresh weight, and chlorophyll concentration and reducing Cr concentrations in roots and leaves by 24.7%-65.7%. In contrast, Si application to the 1-2 cm segment had minimal impact on rice growth or Cr uptake. These results suggest a deep Si application strategy for remediating Cr-contaminated soil. The innovative device provides a scientific foundation for distinguishing element uptake contributions of different root segments and enhancing the utilization efficiency of remediation materials and nutrient management in agriculture.