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Soil fungal diversity and plant resilience under the dual stress of microplastics and heavy metals: A comparative study of lettuce and green onion
Summary
Tiny plastic particles (microplastics) combined with heavy metals in soil can harm the beneficial fungi that help plants grow, while also boosting harmful plant pathogens — and the smaller the plastic pieces, the worse the damage. This mattered most for lettuce grown directly from seed, which absorbed more contamination and showed more stress than green onions grown from seedlings, suggesting the vegetables you buy could carry these pollutants depending on how they were farmed. While this study looked at soil and plant health rather than direct human effects, it raises concerns since these contaminants could potentially make their way into the produce we e
Microplastics are major environmental contaminants due to their persistence and durability. However, research on the combined effects of heavy metals (HMs) and MPs on soil fungi and plant health remains limited. This study investigates the HMs contaminated soils in Tongling, along with polystyrene microplastics (PS-MP) of different sizes (T1 = 106 μm, T2 = 50 μm, and T3 = 13 μm), on soil properties, fungal diversity (including AMF and pathogens), and the growth/ antioxidant activity of Allium fistulosum and Lactuca sativa under two planting methods. Results showed that MP size significantly influenced fungal composition and plant growth, with planting procedure and exposure time playing key roles. PS-MPs increased soil pH, TC, EC, SOM, Cd, and TP while reducing nitrogen, ammonia, and nitrate levels. Alpha diversity declined in rhizosphere soil and Lactuca sativa with the Chao1 index, for example, decreasing by approximately 22% under the smallest MPs treatment in lettuce rhizosphere (T3R) compared to its bulk soil control (LCB). The phylum Blastocladiomycota was absent in T3-treated lettuce. Rhizosphere soils with smaller PS-MPs had a higher concentration of plant pathogens, particularly in lettuce. AMF were more abundant in bulk soil; smaller MPs reduced their abundance, especially in lettuce. Claroideoglomeraceae family was absent in lettuce but present in onion, while the Glomeraceae was highly sensitive to smaller MPs in rhizosphere soil. Growth parameters, membrane leakage, relative water content, and antioxidant activity were significantly affected, especially under T3 conditions. The combination of PS-MPs and HMs had a more severe impact on Lactuca sativa (seeds) than on Allium fistulosum (seedlings). Planting method critically influenced plant resilience and fungal community. Our results highlight the heightened ecological risks associated with small PS-MPs containing HMs, particularly for direct-seeded plants.