Dual Effects of Polyethylene Microplastics on Solanum lycopersicum L.‐Soil Systems: Plant Growth Promotion and Microbial Network Simplification

ABSTRACT

Low‐density polyethylene (LDPE) and high‐density polyethylene (HDPE) particles are primary components of agricultural mulch films. The extensive application and degradation of these films lead to the accumulation of microplastics (MPs) in soil, necessitating an integrated assessment of their impact on crop‐soil systems. Therefore, we assessed the impact of various concentrations of LDPE at 5% w / w (L0505), 10% w / w (L0510) and HDPE at 5% w / w (H2005), at 10% w / w (H2010) on Solanum lycopersicum L. in an 80‐day pot experiment, measuring plant growth, antioxidant enzyme activities and rhizosphere soil properties. The findings revealed that PE‐MPs exerted strong, concentration‐dependent effects on plant growth. Under treatment conditions of L0505, L0510 and H2005, the plant height showed an increase of 28.33%, 36.81% and 34.81% while the dry weight increased to 16.36%, 54.84% and 98.73%, respectively. Conversely, H2010 significantly inhibited growth, reducing dry weight by 50.69%. Plant antioxidant enzyme activities (SOD, POD, CAT) generally increased as a stress response, with POD activity rising by 194.40% under H2010. Soil organic matter (SOM) content increased significantly in all treatments, with the H2010 treatment increasing by 177.61%. H2010 increased available potassium by 32.73% but decreased available phosphorus by 11.70%. The ACE and Chao1 indices indicate that microbial richness showed a decreasing trend in all MPs exposure conditions. Co‐occurrence network analysis suggested altered microbial interactions due to MPs. High‐concentration HDPE reduced network complexity, whereas low concentrations enhanced positive correlations. PLS‐PM revealed that while PE‐MPs positively affected soil chemical properties, they exerted indirect negative effects on plant growth by restructuring the microbial community. Functional prediction indicated enhanced TCA cycle activity and oxidative phosphorylation but suppressed nitrogen and sulphur metabolism in the soil. These findings emphasise the critical influence of MP type and concentration on plant–soil‐microbe interactions, highlighting that while low levels may stimulate growth, high accumulation poses risks to microbial stability and crop health.