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Background and aims <p>Root exudates have been proposed to influence arsenic (As) mobility and speciation in paddy soils. However, how sulfur-rich conditions interact with root exudates to regulate Fe-sulfur-driven As mobilization and speciation remain unclear.</p> Methods <p>As speciation and Fe mineralogy were examined in an anoxic paddy soil microcosm experiment, where citric acid, oxalic acid and glucose were added as root exudates at sulfate concentrations of 0, 5 and 25&#xa0;mM.</p> Results <p>Root exudates enhanced the reduction of Fe (oxy)hydroxides, increasing pore water As concentrations of 11.6–46.3%, with oxalic acid showing the strongest promoting effect, followed by citric acid and glucose. Sulfate reduction promoted the formation of Fe sulfide minerals, which sequestered As and reduced pore water concentrations by 4.6–22.5% relative to sulfate-free treatments. Elevated sulfide fluxes enhanced Fe-sulfide precipitation, thereby strengthening As immobilization. Moreover, relative to sulfate-free treatments, sulfate reduction stimulated microbial As methylation and thiolation, increasing dimethylarsenate (DMA) and dimethylmonothioarsenate (DMMTA) production by 52.6–127.5% and 14.3–99.9%, respectively.</p> Conclusions <p>Root exudates enhance As mobilization by promoting its releases from solid phases into pore water, whereas sulfate reduction partially counteracts this process through incorporation into sulfide minerals. The extent of As immobilization depends on sulfate fluxes. These findings underscore the critical role of sulfate reduction in regulating As mobilization and speciation in paddy soils under simulated rhizosphere conditions.</p>

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Dynamics of sulfate reduction regulate arsenic mobilization and speciation in paddy soils in response to root exudates

  • 期刊论文

  • 发表日期：

    2026年1月2日

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  • Guo-Hao Zhang,
  • Hong-Yan Wang,
  • Jun-Jie Lin,
  • Guo-Xin Sun,
  • Zheng Chen,
  • Zhi-Guo Yu

摘要

Background and aims

Root exudates have been proposed to influence arsenic (As) mobility and speciation in paddy soils. However, how sulfur-rich conditions interact with root exudates to regulate Fe-sulfur-driven As mobilization and speciation remain unclear.

Methods

As speciation and Fe mineralogy were examined in an anoxic paddy soil microcosm experiment, where citric acid, oxalic acid and glucose were added as root exudates at sulfate concentrations of 0, 5 and 25 mM.

Results

Root exudates enhanced the reduction of Fe (oxy)hydroxides, increasing pore water As concentrations of 11.6–46.3%, with oxalic acid showing the strongest promoting effect, followed by citric acid and glucose. Sulfate reduction promoted the formation of Fe sulfide minerals, which sequestered As and reduced pore water concentrations by 4.6–22.5% relative to sulfate-free treatments. Elevated sulfide fluxes enhanced Fe-sulfide precipitation, thereby strengthening As immobilization. Moreover, relative to sulfate-free treatments, sulfate reduction stimulated microbial As methylation and thiolation, increasing dimethylarsenate (DMA) and dimethylmonothioarsenate (DMMTA) production by 52.6–127.5% and 14.3–99.9%, respectively.

Conclusions

Root exudates enhance As mobilization by promoting its releases from solid phases into pore water, whereas sulfate reduction partially counteracts this process through incorporation into sulfide minerals. The extent of As immobilization depends on sulfate fluxes. These findings underscore the critical role of sulfate reduction in regulating As mobilization and speciation in paddy soils under simulated rhizosphere conditions.