Reactive Oxygen Species in Rice Fields: A Review of Generation Mechanisms, Influencing Factors and their Environmental Impacts

Reactive oxygen species (ROS) are ubiquitous in the Earth's surface environments, especially in paddy ecosystems. Despite that ROS are highly reactive and transient, they are continuously produced in rice fields through biotic and abiotic pathways. This may enhance the mobility and toxicity of certain pollutants, elevate greenhouse gas emissions and inhibit rice growth. Understanding ROS dynamics in rice paddies is crucial for mitigating these impacts. However, knowledge gaps persist regarding the species, mechanisms, and factors driving ROS generation, and how these affect biogeochemical cycling of nutrients and contaminants and rice growth in rice fields. This review establishes that ROS hotspots concentrate spatiotemporally at detritusphere-rhizosphere-redox interfaces, exhibiting distinct diurnal cycling with daytime maxima and distance-dependent attenuation due to constrained oxygen diffusion. It integrates dominant ROS production pathways alongside their regulatory mechanisms governed by the speciation and concentrations of photosensitizer/transition metal, O₂ content, straw return and fertilization, and microbial activity. We further highlighted the adverse impacts of these processes driven by ROS, including enhanced pollutant mobility/toxicity, greenhouse gas emissions (CO₂/N₂O), and oxidative damage to rice cells. Additionally, it also elucidates the role of ROS in nutrient cycling (C/N/P/S), pollutant transformation (i.e., heavy metals and organic pollutants) and iron plaque formation on rice roots. Finally, this review suggests future research directions and provides a theoretical basis and new insights into ROS generation and scientific management strategies in rice fields.