Polyethylene microplastics reduce microbe-driven multifunctionality in maize-soybean intercropping ecosystem

Microplastics (MPs) pollution poses a growing threat to agroecosystem functioning, yet its influence on soil microbial communities and ecosystem multifunctionality (ability to maintain multiple functions and services simultaneously) in intercropping system remains poorly understood. Here, we investigated the effects of polyethylene (PE), polypropylene (PP), and polystyrene (PS) MPs (0.1 %, 1 % and 5 %; w/w) on maize-soybean intercropping system, focusing on plant physiology, edaphic property, microbial diversity, and ecosystem multifunctionality. We found that 5 % PP MPs reduced (-29.5 %) while PS MPs improved maize biomass (+18.1 %). Maize experienced increased soluble sugar (+15.4 % to +26.0 %) and protein (+19.3 % to +25.4 %), while soybean exhibited decreased soluble protein (-40.3 % to -18.4 %) under 5 % PE and PP MPs. The 5 % MPs improved soil total carbon (C) and nitrate nitrogen (N), but reduced available (-9.2 % to -6.1 %) and total phosphorus (P) (-21.5 % to -17.8 %). Activity of most soil enzymes involved in C, N and P cycling was promoted by 5 % MPs. Moreover, 5 % MPs decreased bacterial and fungal α diversity, while elevated microbial network complexity. Notably, 5 % PE MPs significantly reduced ecosystem multifunctionality, mainly driven by declines in microbial diversity and soil nutrient availability. Our findings reveal that MPs pollution disrupts plant-microbe-soil interactions, ultimately impairing the multifunctionality of intercropping systems. These results underscore the urgent and prior need to mitigate PE MPs pollution in agricultural soils, especially by reducing the use of PE-source agricultural mulch films, to safeguard ecosystem health and productivity.