Microplastics change soil properties, plant performance, and bacterial communities in salt-affected soils

Microplastics (MPs) are emerging contaminants found globally. However, their effects on soil-plant systems in salt-affected habitats remain unknown. Here, we examined the effects of polyethylene (PE) and polylactic acid (PLA) on soil properties, maize performance, and bacterial communities in soils with different salinity levels. Overall, MPs decreased soil electrical conductivity and increased NH4+-N and NO3−-N contents. Adding NaCl alone had promoting and inhibitive effects on plant growth in a concentration-dependent manner. Overall, the addition of 0.2% PLA increased shoot biomass, while 2% PLA decreased it. Salinity increased Na content and decreased K/Na ratio in plant tissues (particularly roots), which were further modified by MPs. NaCl and MPs singly and jointly regulated the expression of functional genes related to salt tolerance in leaves, including ZMSOS1, ZMHKT1, and ZMHAK1. Exposure to NaCl alone had a slight effect on soil bacterial α-diversity, but in most cases, MPs increased ACE, Chao1, and Shannon indexes. Both MPs and NaCl altered bacterial community composition, although the specific effects varied depending on the type and concentration of MPs and the salinity level. Overall, PLA had more pronounced effects on soil-plant systems compared to PE. These findings bridge knowledge gaps in the risks of MPs in salt-affected habitats. Soil salinization represents one of the most challenging environmental issues. Microplastics (MPs) occur widely in various ecosystems, including salt-affected habitats. However, little is known about the ecological impacts of MPs on soil-plant systems under salinity stress. For the first time, we compared the effects of conventional and biodegradable MPs on soil and plant traits in salt-affected soils. We found that MPs and salt altered soil properties, plant performance and Na uptake. MPs and NaCl co-drove the bacterial community structuring, with more profound consequences from biodegradable MPs. Our results shed light on the ecological risks of MPs in salt-affected ecosystems.