Geochemical weathering and microbial carbon turnover: coupled drivers of greenhouse gas mitigation in basalt-amended paddy soil

Abstract

Increasing agricultural cultivation is a major contributor to greenhouse gas emissions worldwide. Recently, the application of silicate minerals, such as basalt, has gained attention as a strategy to mitigate greenhouse gas emissions from paddy soils. These minerals can enhance carbon sequestration through weathering reactions that consume atmospheric CO₂ as they dissolve. This study investigates not only the weathering effects but also how basalt treatment influences microbial processes in paddy soils, ultimately affecting emissions of carbon dioxide (CO₂) and methane (CH₄). With different concentrations of basalt powder, biotic and abiotic batch systems were constructed and gas emissions, cation dissolution, carbon turnover, and microbial communities were investigated. Microbial respiration led to an increase in CO₂ and CH₄ emissions, however, the gas emissions decreased with higher basalt concentrations. The release of cations such as Si, Ca, and Mg also had a potential role in reducing gas emissions through inorganic carbon trapping. Moreover, the lower dissolved organic carbon (DOC) concentrations were measured under all of the batches, demonstrating the effects of microorganisms. By calculating the turnover of solid organic carbon (SOC) across gas, aqueous, and solid phases, the role of microorganisms in carbon flow was confirmed. Microbial community analysis showed that Methanobacterium decreased in proportion with increasing basalt content. It might be attributed to the thermodynamic suppression imposed by basalt-derived electron acceptors. These results indicate that basalt application can effectively reduce microbial greenhouse gas emissions and could potentially be applied to a variety of soil types beyond just paddy fields.