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Purpose <p>Cadmium (Cd) contamination in soil and its accumulation in rice grains pose serious risks to human health. Biochar can alter soil properties, Cd availability, and rhizosphere enzyme activities, but spatially resolved evidence of these processes remains limited.</p> Methods <p>A 30-day rhizotron experiment was conducted using loofah sponge biochar (LSB) at 0.1%, 0.5%, and 1%, together with a 1% corn straw biochar (CSB) reference treatment, in a Cd-contaminated soil–rice system. Planar optodes, soil zymography, and diffusive gradients in thin films (DGT) were used to characterize rhizosphere pH, phosphatase activities, and Cd lability.</p> Results <p>Two-dimensional pH imaging showed that biochar alleviated rhizosphere acidification, increasing soil pH by 0.01–0.49 units, with a clear dose-dependent increase under LSB application. Biochar also increased soil organic carbon by 1.3–77.8% and Olsen-P by 2.3–39.7%, indicating altered soil C and P status. Soil zymography revealed contrasting phosphatase responses: rhizosphere acid phosphatase(ACP) activity increased by 5.3–125.5%, whereas alkaline phosphatase(ALP) activity decreased by 24.6–40.6% in the rhizosphere and showed a similar decline in bulk soil. Rhizosphere <i>C</i><sub>DGT</sub>-Cd decreased by 25.7–68.6%, while Cd concentrations in roots and shoots decreased by 24.2–51.3% and 16.9–63.7%, respectively. Partial least squares path modeling indicated associations among soil pH, DGT-measured Cd, plant Cd accumulation, and plant growth.</p> Conclusion <p>The integration of spatial pH and enzyme imaging with DGT-based Cd assessment revealed root-associated heterogeneity that would not be captured by conventional bulk-soil measurements.</p>

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In situ mapping of rhizosphere processes: biochar-mediated cadmium immobilization and rhizosphere microenvironment regulation

  • 期刊论文

  • 发表日期：

    2026年7月24日

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  • Baoying Wang,
  • Zhao Wei,
  • Haitao Sun,
  • Xing Liu,
  • Li Zhang,
  • Jianyu Lin,
  • Jun Luo

摘要

Purpose

Cadmium (Cd) contamination in soil and its accumulation in rice grains pose serious risks to human health. Biochar can alter soil properties, Cd availability, and rhizosphere enzyme activities, but spatially resolved evidence of these processes remains limited.

Methods

A 30-day rhizotron experiment was conducted using loofah sponge biochar (LSB) at 0.1%, 0.5%, and 1%, together with a 1% corn straw biochar (CSB) reference treatment, in a Cd-contaminated soil–rice system. Planar optodes, soil zymography, and diffusive gradients in thin films (DGT) were used to characterize rhizosphere pH, phosphatase activities, and Cd lability.

Results

Two-dimensional pH imaging showed that biochar alleviated rhizosphere acidification, increasing soil pH by 0.01–0.49 units, with a clear dose-dependent increase under LSB application. Biochar also increased soil organic carbon by 1.3–77.8% and Olsen-P by 2.3–39.7%, indicating altered soil C and P status. Soil zymography revealed contrasting phosphatase responses: rhizosphere acid phosphatase(ACP) activity increased by 5.3–125.5%, whereas alkaline phosphatase(ALP) activity decreased by 24.6–40.6% in the rhizosphere and showed a similar decline in bulk soil. Rhizosphere CDGT-Cd decreased by 25.7–68.6%, while Cd concentrations in roots and shoots decreased by 24.2–51.3% and 16.9–63.7%, respectively. Partial least squares path modeling indicated associations among soil pH, DGT-measured Cd, plant Cd accumulation, and plant growth.

Conclusion

The integration of spatial pH and enzyme imaging with DGT-based Cd assessment revealed root-associated heterogeneity that would not be captured by conventional bulk-soil measurements.