Intercropping strategies to mitigate PLA-Pb stress and enhance legume growth: A mechanistic study

Biodegradable microplastics such as polylactic acid (PLA) are emerging contaminants that can exacerbate crop stress, particularly when combined with heavy metals like lead (Pb) in agricultural soils. While intercropping is known to enhance crop resilience, the specific mechanisms for mitigating combined PLA-Pb stress remain poorly understood. This study investigated the potential and underlying mechanisms of faba bean-wheat intercropping to mitigate combined PLA-Pb stress by assessing faba bean disease incidence, growth performance, Pb(II) accumulation, and rhizosphere microenvironment. Results demonstrated that faba bean-wheat intercropping effectively alleviated combined PLA-Pb stress. Compared to monoculture, intercropping significantly increased shoot and root biomass (by 29.16% and 27.67%), reduced Fusarium wilt incidence and disease index (by 19.00% and 18.57%), and decreased Pb(II) accumulation in leaves and roots (by 21.14% and 17.30%). Additionally, intercropping enhanced the plant antioxidant system (by increasing SOD, CAT, and APX activities), alleviated oxidative stress, and improved rhizosphere properties by reducing available Pb(II) content (by 23.87%) and increasing nutrient availability and enzyme activities. Furthermore, intercropping enriched beneficial rhizosphere bacteria (e.g., Sphingomonas), upregulated defense-related metabolites (including phenylpropanoids, alkaloids, flavonoids), and activated key resistance-related pathways such as α-linolenic acid metabolism. The partial least squares path model confirmed that intercropping promotes plant growth and disease control primarily through rhizospheric microbial and biochemical reprogramming. This research illustrates how intercropping systemically alleviates PLA-Pb co-toxicity, highlights the practical value of intercropping in managing combined pollution stress, and provides a mechanistic basis for its application in sustainable legume production.