Biodegradable microplastics disrupt root exudate driven plant-microbe interactions, compromising plant growth and rhizosphere microenvironment health.

Abstract

Microplastics (MPs) pollution already posed a serious threat to human health. Biodegradable (bio) plastics serve as alternatives to traditional plastics. However, the ecological impact of bio-MPs has not been adequately assessed. This study evaluates the effects of two types of bio-MPs (poly (butylene adipate-co-terephthalate) (PBAT) and polylactic acid (PLA)) on plant growth and the rhizosphere soil microenvironment. Exposure to bio-MPs significantly decreased tomato growth, soil enzyme activities, and rhizosphere microbial diversity. In addition, bio-MPs significantly reduced the abundance of beneficial microorganisms (growth-promoting, nutrient cycling, stress resistance) in the rhizosphere soil. The secretion levels of several root exudates decreased significantly, including citric acid, quinic acid, indole, p‑coumaric acid, and flavone. This decrease led to alterations in multiple metabolic pathways: the TCA cycle, the biosynthesis of phenylalanine, tyrosine, and tryptophan, and the phenylpropanoid biosynthesis pathway. Meanwhile, these specific metabolites showed a significant positive correlation with beneficial rhizosphere microorganisms. Compared with traditional MPs, these findings suggests that the presence of bio‑MPs may interfere with normal plant-microbe interactions, which is further associated with an imbalance in the rhizosphere ecological microenvironment and may ultimately contribute to impaired plant growth. In the meantime, the beneficial effects of root exudates on plant resistance against bio‑MP toxicity have also received preliminary confirmation. This finding provides valuable evidence for evaluating the impact of bio-plastics on plant rhizosphere soil health.