The absorption, immobilization, and response mechanism of Leymus chinensis to microplastics and nanoplastics

Microplastics and nanoplastics (M/NPs), as a newly emerging group of pollutants of global concern, have drawn widespread attention owing to their potential hazards. Previous studies have primarily focused on the responses of aquatic plants, model plants, and crops to microplastics and nanoplastics, while there is only limited understanding of their ecological effects on terrestrial plants. This study utilized Sheepgrass (Leymus chinensis), a plant of significant ecological value, as the subject to investigate the physiological, biochemical, and molecular-level effects of 50 nm and 20 μm polymethyl methylacrylate. The results indicated that both particle sizes of M/NPs negatively affected L. chinensis by inhibiting its growth, reducing the content of chlorophyll, weakening photosynthesis by inhibiting the capture of light energy and transport of electrons, and increasing the amount of oxidative stress by accumulating hydrogen peroxide and superoxide anions. Smaller particles and higher concentrations of M/NPs were more toxic. Fluorescence visualization and quantitative analyses revealed that smaller particles primarily entered the plant via the apoplast pathway, while larger particles caused mechanical damage to the root system owing to their size effects. A transcriptomic analysis showed that treatments of different particle sizes significantly enriched the expression of multiple pathway genes associated with the stress responses. Notably, L. chinensis enhances its tolerance and the ability to detoxify the stress caused by M/NPs by regulating the antioxidant system, accumulating proline, and activating the phenylpropanoid biosynthetic pathway. This study provides new insights into the mechanisms of toxicity of M/NPs and offers an important theoretical basis to utilize key ecological species, such as L. chinensis, in soil remediation.