Interactive effects of warming and biochar addition on photosynthesis and greenhouse gas emissions in a paddy system

Global warming and rice cultivation are both significant drivers of greenhouse gas emissions, with methane (CH₄) representing a potent short lived climate forcer. Understand the interactive effects of rising temperatures and soil management practices in regulating carbon fixation and emissions is essential for developing climate-smart rice agroecosystems. Biochar amendment has been proposed to improve soil fertility and mitigate greenhouse gas emissions, yet its interactive effects with warming remain insufficiently understood. A synergistic assessment of warming and biochar application is therefore necessary to evaluate their integrated potential for climate mitigation and sustainable rice production.

A controlled pot experiment using a water bath warming system was established to investigate the interactive effects of warming and biochar amendment. Four treatments were implemented: (1) conventional fertilization (NPK, control), (2) warming (NPK + H), (3) biochar addition (NPK + BC), and (4) combined warming and biochar (NPK + BC + H). Throughout the growing season, key environmental variables, including soil temperature, moisture, and electrical conductivity were continuously monitored. In parallel, rice growth traits and photosynthetic parameters were measured periodically. Greenhouse gas fluxes (CO₂, CH₄, and N₂O) were regularly quantified to assess treatment effects on emissions dynamics.

The experiment revealed critical interactions between warming and biochar. Their effects were often divergent when applied singly but convergent in combination. Specifically, while biochar alone stimulated CO₂ and CH₄ fluxes, and warming independently raised soil temperature, their combined application did not yield additive outcomes. Instead, it suppressed the biochar-induced increase in CO₂ and CH₄, demonstrating a clear interactive mitigation effect. Furthermore, this combination synergistically promoted rice photosynthesis and growth, and all amendment treatments reduced N₂O emissions relative to the NPK control.

Our findings demonstrate that warming and biochar amendment interactively regulate soil-plant processes and greenhouse gas fluxes in rice paddies, primarily through an antagonistic interaction that reverses the sole effect of biochar on CH₄ and CO₂ emissions. This shift indicates a fundamental change in microbial activity and carbon metabolism under combined treatment. Moreover, the synergy between warming and biochar enhanced photosynthetic carbon fixation, illustrating a dual mechanism that simultaneously optimizes carbon gain and attenuates carbon loss. These results provide mechanistic insight into how integrated management can reconcile productivity with climate mitigation, supporting the development of climate-smart strategies for rice agroecosystems under future warming scenarios.