Responses of rice (Oryza sativa L.) plant growth, grain yield and quality, and soil properties to the microplastic occurrence in paddy soil

Purpose Agricultural soil has been recognized as a major sink of microplastic, an emerging pollutant to environmental biodiversity and ecosystem. However, the impacts of microplastic on soil-plant systems (e.g., crop growth, grain yield and amino acid content, nitrogen uptake capacity, and soil properties) remain largely unknown. Methods Four typical microplastics, i.e., polythene (PE, 200 mu m), polyacrylonitrile (PAN, 200 mu m), and polyethylene terephthalate (PET) in diameter of 200 mu m and 10 mu m (PET200 and PET10), were tested to assess the consequent aforementioned responses under rice (Oryza sativa L.) paddy soil in a mesocosm experiment. Results Microplastics multiply influenced the soil pH, NH4+-N and NO3--N contents, which effects were depended on the rice growth stage and plastic type. Overall, microplastics significantly decreased the soil urease activity by 5.0-12.2% (P < 0.05). When exposed to PAN and PET (in both diameter of 200 mu m and 10 mu m), there were significantly 22.2-30.8% more grain yield produced, compared to the control (P < 0.05), which was attributing to the higher nitrogen uptake capacity of rice grain. Meanwhile, microplastics exhibited nominal influences on rice plant height, tillering number, leaf SPAD, and NDVI. The amino acids were affected by microplastic, depending on the types of plastics and amino acids. Conclusion This study provides evidence that microplastic can affect the development and final grain yield, amino acid content, nitrogen uptake capacity of rice, and some major soil properties, while these effects vary as a function of plastic type. Our findings highlight the positive impacts that could occur when the presence of microplastics in paddy soil.