Key Takeaways & Executive Findings
- •• • Biochar amendment increased maximum cumulative CH4 emission to (66.23±16.20) μmol, a 4.4-fold increase over control (15.14±0.18) μmol, demonstrating its potential to enhance methanogenesis in paddy soils, which is critical for assessing biochar's net greenhouse gas impact. • • AQDS addition suppressed CH4 accumulation to (1.04±0.09) μmol, a 93% reduction relative to control, due to sulfate acting as a competitive electron acceptor; this highlights the risk of using sulfate-containing amendments to mitigate CH4. • • Combined biochar and AQDS resulted in intermediate CH4 accumulation of (12.71±0.32) μmol, which is 19% of biochar alone and 12-fold higher than AQDS alone, indicating an additive effect where biochar's stimulation is partially offset by AQDS-induced electron competition. • • The combined treatment favored the acetoclastic methanogenesis pathway, which produces less CH4 per unit acetate, explaining the lower CH4 yield compared to biochar alone; this mechanistic insight is essential for predicting CH4 emissions under co-amendment scenarios.
Abstract
Paddy soils are a major source of agricultural methane (CH4) emissions. Biochar is widely applied to paddy soils, while dissolved organic matter (DOM) is ubiquitous; both can regulate CH4 emissions by mediating electron transfer processes, yet their synergistic mechanisms remain unclear. This study investigated the individual and combined effects of biochar and the DOM model compound anthraquinone-2,6-disulfonic acid (AQDS) on CH4 emissions from paddy soil during incubation. Biochar amendment increased DOM concentration and accelerated extracellular electron transfer, resulting in a maximum cumulative CH4 emission of (66.23±16.20) μmol, four-fold higher than the control (15.14±0.18) μmol. In contrast, AQDS addition markedly suppressed CH4 accumulation to (1.04±0.09) μmol, attributed to sulfate introduction as a competitive electron acceptor, despite enhanced electron exchange. The combined biochar-AQDS treatment yielded intermediate CH4 accumulation of (12.71±0.32) μmol. Although DOM availability increased, sulfate-driven electron competition inhibited methanogens, and the combined treatment favored the acetoclastic methanogenesis pathway, which produces less CH4 per unit acetate, resulting in lower emissions than biochar alone but higher than AQDS alone, indicating an additive effect. These findings elucidate the mechanisms by which biochar and DOM jointly regulate CH4 emissions from paddy soils, providing a theoretical basis for agricultural management.
1. Introduction
Agricultural methane emissions from paddy soils constitute a significant source of greenhouse gases, with global warming potential 28 times that of CO2 over a 100-year horizon. Biochar amendment has been widely promoted for carbon sequestration and soil improvement, yet its impact on CH4 emissions is contentious, with studies reporting both stimulation and suppression. Concurrently, dissolved organic matter (DOM) is ubiquitous in paddy soils and participates in redox reactions, potentially influencing methanogenesis. However, the interactive effects of biochar and DOM on CH4 emissions have remained largely unexplored, hindering accurate prediction of net greenhouse gas balance in biochar-amended paddies.
This study addresses this knowledge gap by systematically evaluating the individual and combined effects of biochar and the DOM surrogate AQDS on CH4 emissions from paddy soil. By quantifying CH4 accumulation and analyzing electron transfer pathways, the research delineates the mechanisms underlying the observed additive effect, providing critical data for optimizing biochar application strategies to minimize CH4 emissions while maintaining soil health.
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HE Ting, CHENG Chen, WU Yufei, ZHAO Zhuoxi, WANG Zhao, ZHANG Peng (2026). Combined Effects of Biochar and Dissolved Organic Matter Surrogate AQDS on Methane Emissions from Paddy Soil. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025022801
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Frequently Asked Questions
What is the mechanism by which biochar increases CH4 emissions in paddy soil?
Biochar enhances CH4 emissions by increasing DOM concentration and accelerating extracellular electron transfer rates, as evidenced by a maximum cumulative CH4 emission of (66.23±16.20) μmol, four-fold higher than control. This suggests biochar provides additional substrates and facilitates electron shuttling, promoting methanogenic activity.
How does AQDS suppress CH4 emissions despite accelerating electron transfer?
AQDS introduces sulfate as a competitive electron acceptor, which outcompetes methanogens for electrons, leading to a drastic reduction in CH4 accumulation to (1.04±0.09) μmol, a 93% decrease relative to control. This indicates that the presence of alternative electron acceptors can override the benefits of enhanced electron transfer.
What is the combined effect of biochar and AQDS on CH4 emissions, and what is the underlying mechanism?
The combined treatment yields intermediate CH4 accumulation of (12.71±0.32) μmol, which is lower than biochar alone but higher than AQDS alone, indicating an additive effect. This is attributed to increased DOM availability (from biochar) being offset by sulfate-driven electron competition (from AQDS), and a shift toward the acetoclastic methanogenesis pathway, which produces less CH4 per unit acetate.
What are the implications of these findings for agricultural practices involving biochar application?
The results suggest that biochar application alone may increase CH4 emissions, potentially offsetting its carbon sequestration benefits. However, co-application with sulfate-containing amendments like AQDS could mitigate this increase, but the trade-off is a reduction in overall methanogenic activity. Therefore, field-specific management strategies are needed to balance CH4 mitigation and soil carbon goals.
How does the shift to acetoclastic methanogenesis in the combined treatment affect CH4 production efficiency?
The acetoclastic pathway produces less CH4 per unit acetate compared to hydrogenotrophic methanogenesis, leading to lower CH4 yields. In the combined treatment, this shift, along with electron competition, results in CH4 accumulation of only 12.71 μmol, which is 19% of the biochar-only treatment, indicating a less efficient methanogenic process.
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