Microplastics pollution from different plastic mulching years accentuate soil microbial nutrient limitations

Microplastics (MPs) are major global environmental pollutants that have been extensively detected in agroecosystems. However, researches on their distribution and fates in farmland as well as their potential impacts on soil ecosystems are limited, especially studies on the influences of MPs on enzymes associated with carbon (C), nitrogen (N), and phosphorus (P) cycling and microbial nutrient limitations characterized by enzymatic stoichiometry are missing. In this study, we investigated the MPs characteristics under different continuous mulching management years (3, 6, 10, 15, and 20a) of tobacco fields in Enshi Prefecture, China, and identified the mechanisms of MPs pollution on soil microbial nutrient limitations. The results showed that the abundance of MPs varied from 647 to 2840 items/kg. Films, fibers and small-sized particles (0–1.0 mm) were the predominant types and size, respectively, and increased significantly with the increase of planting years. A vector analysis of enzyme activity suggested that microbial metabolism was limited both with C and P. The correlation analysis demonstrated that MPs pollution and soil properties were significantly linked to microbial nutrient limitations. Meanwhile, partial least squares path model (PLS-PM) revealed that MPs abundance exacerbated microbial limitation mainly by directly affecting soil microbial properties, followed by soil physical properties and soil nutrients, whereas MPs size and shapes indirectly exacerbated microbial nutrient limitation by significantly influencing MPs abundance. These results demonstrated that contamination of soil with MPs may have deleterious effects on soil key functions related to microbial metabolism, nutrient cycling, etc. Changes in soil properties and functions can damage plant growth and development, which may further affect crop yield and quality. This study provided a new theoretical basis for the response of soil microbial metabolism to MPs pollution and facilitated a better understanding and estimation of the environmental behavior and ecological risk of MPs in agricultural fields.