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Purpose <p>Humic acids (HAs) are widely recognized as soil amendments that improve soil quality, but their specific influence on carbon turnover dynamics in soils has yet to be fully elucidated. This study investigated how different types of HAs regulate the transformation pathways of soil organic carbon components and their underlying microbial control mechanisms.</p> Materials and methods <p>Neutral (Guangdong) and acidic (Jiangxi) paddy soils were spiked with three HAs—synthetic (straw-derived, SHA), peat-derived (PHA), and compost-derived (cattle manure, CHA)—at 5&#xa0;g/kg. Under 30-day anaerobic incubation, CH<sub>4</sub> and CO<sub>2</sub> emissions, soil organic carbon (SOC), environmental parameters, and microbial communities were monitored.</p> Results and discussion <p>In neutral and acidic soils, SHA significantly increased CH<sub>4</sub> production by 68.32-fold (from 0.13 to 8.8 µmol/g) and 23.3%, respectively. It also significantly elevated SOC by 21.82% and 20.39%. In contrast, PHA and CHA exerted lesser effects on carbon turnover. Microbial analysis revealed that SHA significantly altered microbial community structure and carbon metabolic functions, with promoted acetate-type and hydrogen-dependent methanogenesis. Moreover, SHA stimulated the DC/4-HB pathway but inhibited rTCA and WL pathways, whereas PHA and CHA exhibited opposite trends. Correlation indicated that structure-dependent effect of HAs on microbial carbon turnover. SHA, with its high aliphatic content, was the most effective driver of carbon transformation and methane emissions, surpassing the aromatic macromolecules PHA and CHA.</p> Conclusion <p>These findings indicate that HAs’ chemical complexity drives short-term microbial carbon turnover. However, given the substantial CH₄ emissions induced by SHA, long-term assessments are essential before recommending specific HA amendments for soil carbon sequestration.</p>

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Microbial mechanisms of carbon turnover in humic acid-amended paddy soils

  • 期刊论文

  • 发表日期：

    2026年7月11日

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  • Shuwei Sun,
  • Xiaoxue Zhang,
  • Shuigang Wen,
  • Senpei Lin,
  • Minghao He,
  • Lihua Zhou,
  • Yong Yuan

摘要

Purpose

Humic acids (HAs) are widely recognized as soil amendments that improve soil quality, but their specific influence on carbon turnover dynamics in soils has yet to be fully elucidated. This study investigated how different types of HAs regulate the transformation pathways of soil organic carbon components and their underlying microbial control mechanisms.

Materials and methods

Neutral (Guangdong) and acidic (Jiangxi) paddy soils were spiked with three HAs—synthetic (straw-derived, SHA), peat-derived (PHA), and compost-derived (cattle manure, CHA)—at 5 g/kg. Under 30-day anaerobic incubation, CH4 and CO2 emissions, soil organic carbon (SOC), environmental parameters, and microbial communities were monitored.

Results and discussion

In neutral and acidic soils, SHA significantly increased CH4 production by 68.32-fold (from 0.13 to 8.8 µmol/g) and 23.3%, respectively. It also significantly elevated SOC by 21.82% and 20.39%. In contrast, PHA and CHA exerted lesser effects on carbon turnover. Microbial analysis revealed that SHA significantly altered microbial community structure and carbon metabolic functions, with promoted acetate-type and hydrogen-dependent methanogenesis. Moreover, SHA stimulated the DC/4-HB pathway but inhibited rTCA and WL pathways, whereas PHA and CHA exhibited opposite trends. Correlation indicated that structure-dependent effect of HAs on microbial carbon turnover. SHA, with its high aliphatic content, was the most effective driver of carbon transformation and methane emissions, surpassing the aromatic macromolecules PHA and CHA.

Conclusion

These findings indicate that HAs’ chemical complexity drives short-term microbial carbon turnover. However, given the substantial CH₄ emissions induced by SHA, long-term assessments are essential before recommending specific HA amendments for soil carbon sequestration.