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Polylactic acid microplastics inhibit Cd accumulation and growth of Solanum nigrum L.: Insights from microbial communities and metabolomic profiles
Summary
Researchers found that polylactic acid microplastics in soil reduced cadmium uptake and inhibited biomass growth in the cadmium hyperaccumulator Solanum nigrum, altering soil microbial communities and metabolomic profiles in ways that could impair phytoremediation.
Biodegradable microplastics (MPs) are increasingly promoted as environmentally friendly alternatives. However, their interactive effects with heavy metals on phytoremediation processes remain poorly understood. The co-occurrence of MPs and heavy metals, particularly cadmium (Cd), poses potential risks to crop safety and phytoremediation strategies. This study firstly focused on the effects of polylactic acid microplastics (PLA-MPs) on Cd accumulation and biomass in Solanum nigrum L. (S. nigrum), a known Cd hyperaccumulator, and investigated the underlying mechanisms in plant-soil system. The study found that PLA-MP addition significantly reduced Cd accumulation in S. nigrum by suppressing plant growth and limiting Cd uptake. Metabolomic analysis revealed that co-exposure to PLA-MPs and Cd significantly inhibited auxin biosynthesis and accelerated chlorophyll degradation, contributing to growth inhibition. Toxic stress further reduced biomass, as indicated by elevated antioxidant enzyme activity and malondialdehyde (MDA) content. Co-exposure also activated biosynthetic pathways for key amino acids and secondary metabolites, including arginine, cysteine, methionine, and cinnamic acids and its derivatives. Moreover, PLA-MPs altered soil physicochemical properties, functional group composition, and microbial community structure, resulting in reduced Cd bioavailability. Importantly, the genera Azotobacter, Citrifermentans and Beijerinckia were significantly enriched and constituted a potential microbial mechanism underpinning the observed PLA-MP biodegradation and enhanced Cd tolerance under combined exposure. The decrement of soil available Cd content might relate to the DEV008 and Mesorhizobium abundance decreased. The present findings provide novel and comprehensive insights into the complex plant-soil-microbe interactions governing heavy metal accumulation by hyperaccumulators under combined stress from biodegradable MPs and Cd.