Modulation of soil microenvironment and plant gene expression by earthworms reduces polypropylene microplastic-induced growth stress in Chinese milk vetch (Astragalus sinicus L.)

Earthworms can mitigate the detrimental effects of polypropylene microplastics (PP-MPs) on plant growth. This study employed pot-grown experiments to investigate how earthworms mitigate growth stress in Astragalus sinicus L. (CMV) exposed to PP-MPs, by evaluating growth and physiological indicators, characterizing soil physicochemical properties, and analyzing gene expression CMV. The results showed that 1 % of PP-MPs dramatically reduced the height and shoot dry weight of CMV by 27.83 % and 19.96 %, respectively. The addition of earthworms resulted in a 49.8 % rise in height and a 32.26 % increase in shoot dry weight. The amounts of chlorophyll, nitrogen, phosphorus, and soluble sugars also rose significantly, while oxidative stress decreased. Additionally, the contents of soil organic carbon, total nitrogen, ammonium nitrogen, alkaline nitrogen, and accessible phosphorus increased by 10.66 % to 21.89 %, and the activities of urease, acid phosphatase, and sucrase increased by 11.52 % to 75.64 %. The transcriptomic analysis revealed that earthworm activity led to the upregulation of genes related to protein synthesis and energy metabolism in CMV's roots. Thus, earthworms alleviate the adverse effects of PP-MPs on CMV by reducing oxidative stress, enhancing physiological metabolic activity, increasing soil enzyme activity and nutrient availability, and up-regulating the expression of growth-related genes in the roots. This study reveals how earthworms mitigate the stress caused by PP-MPs on the growth of CMV, providing a theoretical reference for alleviating the adverse effects of microplastic pollution on plant growth. These findings highlight the ecological significance of earthworms in enhancing plant resilience under conditions of microplastic contamination, offering sustainable solutions for soil remediation. • Exposure to 1 % PP-MPs induced oxidative stress in CMV, disrupted nutrient uptake, and inhibited growth. • The addition of earthworms in PP-MPs-polluted soils can lead to an increase in CMV biomass. • Earthworm activity has upregulated the expression of genes related to energy metabolism and protein synthesis. • Earthworms raised the nutritious content in PP-MPs contaminated soil.