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

## TL;DR

This study uses imaging to show how Celosia argentea plants adapt their root zone under cadmium stress, revealing changes in oxygen, pH, and CO2.

## Contribution

The study introduces planar optode imaging to reveal spatio-temporal microecological changes in the rhizosphere under cadmium stress.

## Key findings

- Oxygen hotspots were concentrated near root surfaces, with elevated CO2 reflecting active root metabolism.
- Under cadmium stress, initial suppression of oxygen was followed by expansion of oxygen-enriched zones and persistent pH elevation.
- These changes suggest coordinated regulation of the rhizosphere, potentially supporting plant adaptation and microbial activity.

## Abstract

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 Celosia argentea, 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.