Photochemically generated reactive oxygen species (ROS) are widespread on the earth’s surface under sunlight irradiation. However, the nonphotochemical ROS generation in surface water (e.g., paddy overlying water) has been largely neglected. This work elucidated the drivers of nonphotochemical ROS generation and its spatial distribution in undisturbed paddy overlying water, by combining ROS imaging technology with in situ ROS monitoring. It was found that H₂O₂ concentrations formed in three paddy overlying waters could reach 0.03–16.9 μM, and the ROS profiles exhibited spatial heterogeneity. The O₂ planar-optode indicated that redox interfaces were not always generated at the soil–water interface but also possibly in the water layer, depending on the soil properties. The formed redox interface facilitated a rapid turnover of reducing and oxidizing substances, creating an ideal environment for the generation of ROS. Additionally, the electron-donating capacities of water at soil–water interfaces increased by 4.5–8.4 times compared to that of the top water layers. Importantly, field investigation results confirmed that sustainable •OH generation through nonphotochemical pathways constituted of a significant proportion of total daily production (>50%), suggesting a comparable or even greater role than photochemical ROS generation. In summary, the nonphotochemical ROS generation process reported in this study greatly enhances the understanding of natural ROS production processes in paddy soils.

中文翻译：

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稻田土壤-水界面的强烈物质交换促进上覆水中活性氧的非光化学形成

在阳光照射下，光化学产生的活性氧（ROS）广泛存在于地球表面。然而，地表水（例如稻田覆盖的水）中非光化学活性氧的产生在很大程度上被忽视了。这项工作通过将 ROS 成像技术与原位ROS 监测相结合，阐明了非光化学 ROS 生成的驱动因素及其在未受干扰的稻田覆盖水中的空间分布。结果发现，三种稻田覆盖水域中形成的H ₂ O ₂浓度可达0.03-16.9 μM，并且ROS分布表现出空间异质性。 O ₂平面光极表明，氧化还原界面并不总是在土壤-水界面处产生，也可能在水层中产生，具体取决于土壤特性。形成的氧化还原界面促进还原物质和氧化物质的快速周转，为ROS的产生创造了理想的环境。此外，土-水界面水的供电子能力比顶层水层增加了4.5-8.4倍。重要的是，现场调查结果证实，通过非光化学途径可持续产生•OH 占每日总产量的很大一部分（>50%），这表明其作用与光化学ROS 产生相当甚至更大。总之，本研究报道的非光化学活性氧生成过程极大地增强了对水稻土中天然活性氧产生过程的理解。