Effects of Polyamide Microplastics with Different Concentrations on Cotton Seed Germination and Seedling Growth

Background Pollution of microplastics (MPs) in agricultural ecosystems has attracted increasing attention. However, compared to staple food crops such as corn, as well as vegetable crops like lettuce, fewer studies have evaluated the ecotoxicity of MPs to cotton due to the concentrated cultivation and production of cotton in specific regions of China, particularly Xinjiang. In this study, the effects of polyamide microplastics (PA-MPs, 75 µm) on the germination and emergence stages of three types of cotton seeds (CCRI 96A, Z 201 and Z 113) were investigated. Batch hydroponic germination tests and sand culture seedling emergence tests were set up to study the effects of PA-MPs on cotton biological characteristics such as seed germination rate, seedling emergence rate, growth characteristics, root traits, leaf area and biomass. Results Results showed that the adverse effect of PA-MPs on germination rate increased in a concentration-dependent manner under hydroponic conditions. At the highest concentration (1000 mg·L ^− 1 ), the germination potential, germination index and vigor index of 96A decreased significantly compared to the control check (CK), and the biomass of 96A and 113 also reduced obviously. The germination index of 201 had a significant drop at high concentrations (500, 1000 mg·L ^− 1 ). Then 113 was selected for sand culture seedling emergence test, the results showed that PA-MPs had a certain inhibitory effect on leaf area, stem length, biomass, root traits, etc. of seedlings, and the inhibitory effect of 100 mg·kg ^− 1 PA-MPs was stronger. Conclusions In the hydroponic germination test, plants of cotton showed a dose-dependent response to four concentrations of PA-MPs, with higher concentration being more toxic. In the sand culture test, PA-MPs had no effect on the emergence rate of seedling, but it inhibited the leaf area, stem length, biomass and root traits of cottons, and the low concentration treatment had exerted a stronger ecotoxicity effect. These findings can provide a theoretical basis for the toxicity of MPs in soil to plants.