Planar Optode Imaging Reveals Spatio-Temporal Heterogeneity of Rhizosphere Microecology in Celosia argentea Under Cadmium Stress

Understanding rhizosphere microscale processes is essential for evaluating plant-soil interactions under heavy metal stress. In this study, planar optode imaging was used to investigate the spatio-temporal distribution of O₂, pH, and CO₂ in the rhizosphere of <i>Celosia argentea</i>, a Cd hyperaccumulator, grown in Cd-contaminated and uncontaminated soils. The results demonstrated pronounced spatial heterogeneity, with O₂ hotspots concentrated near root surfaces, localized rhizospheric alkalinization at root tips, and elevated CO₂ levels reflecting active root metabolism. Under Cd stress, O₂ levels were initially suppressed, while pH and CO₂ increased, indicating adaptive physiological responses. As plant growth progressed, O₂-enriched zones expanded, pH elevation persisted, and CO₂ efflux continued, suggesting coordinated regulation of the rhizospheric microenvironment. These changes may influence microbial activity and nutrient dynamics in the rhizosphere, potentially supporting root function and plant adaptation under metal stress. This study provides mechanistic insights into root-induced microenvironmental regulation under Cd stress and demonstrates the potential of planar optode imaging for assessing plant-driven remediation processes in contaminated soils.