Low phosphorous and polyethylene microplastics synergistically increase Cd uptake in Lolium rigidum: Insights into underlying mechanisms

Soil cadmium (Cd) contamination poses serious risks to plant productivity and human food safety. Farmlands contaminated with Cd are often simultaneously affected by microplastics (MPs) and low phosphorus (LP) availability. This study investigated the combined effects of Cd, LP, and polyethylene microplastics (PE) on Cd uptake in two ryegrass (Lolium rigidum) genotypes, WALR60 and SULR1, contrasting in their sensitivity to PE stress. Both LP and PE treatments significantly enhanced Cd accumulation in plants. A synergistic interaction between LP and PE further increased Cd uptake and impaired plant growth, with the genotype SULR1 showing particular sensitivity to PE stress. Mechanistically, LP and PE promoted Cd^{2 +} influx, likely through Ca²⁺-permeable channels, and upregulated key metal transporter genes such as NRAMP5 and IRT1. Furthermore, PE altered the subcellular distribution of Cd in the sensitive genotype by reducing its sequestration in the cell wall and increasing its accumulation in organelles, thereby enhancing cellular toxicity. Interestingly, for elements such as P and Ca, no significant three-way interaction (Cd × LP × MP) was observed; instead, the combined effect was best presented as Cd + LP × MP. The significant Cd × LP × MP effect on biomass of the sensitive genotype may result from the integrated regulation of multiple physiological networks. Overall, this study provides new insights into plant adaptive responses under combined Cd, LP, and MP stresses, contributing to a better understanding of complex pollution scenarios in agricultural soils.