Responses of cotton growth, physiology, and soil properties to polyethylene microplastics in arid areas

Microplastics (MPs), as a global environmental issue, have unclear impacts on agricultural ecosystems. Cotton, as a major agricultural crop in Xinjiang, requires plastic film covering to ensure its yield. The widespread use of plastic film (commonly made of polyethylene) in cotton cultivation has led to significant concerns about microplastic pollution in cotton fields. However, there is limited research on the effects of MPs on cotton growth and cotton field ecosystems. This study investigates the effects of different concentrations and particle sizes of polyethylene microplastics (PE-MPs) on the physiological changes in cotton plants and the physicochemical properties of the soil. The results show that cotton seedling growth was inhibited in all treatment groups, with a clear dose-dependent effect. In the 200 μm^-1wt% treatment group, the cotton seedlings' antioxidant system experienced severe stress, reflected by significant increases in malondialdehyde and total soluble proteins by 58.95% and 94.29%, respectively, which suppressed plant growth and caused a significant reduction in cotton plant height by 41.95%. Additionally, the inhibition of leaf photosynthesis by PE-MPs was more pronounced as the particle size decreased. Under higher concentrations (1wt%, 3wt%), the transpiration rate (Tr) and stomatal conductance (Gs) were significantly suppressed. In the 2 μm^-1wt% treatment group, Gs and Tr decreased significantly by 44.35% and 36.21%, respectively, compared to the control group. Furthermore, the addition of PE-MPs significantly increased the organic matter and available nitrogen content in the soil, with a dose-dependent effect. At the highest concentration (3wt%), the available nitrogen content increased by 1.78, 1.86, and 1.68 times, respectively, compared to the control group. These findings demonstrate the impact of PE-MPs on cotton seedlings and soil properties, providing strong evidence for the ecological risks of MPs in plastic film-covered agricultural fields.