Growth and physiological responses to microplastics exposure in Brassica chinensis L. seedlings

Background Microplastics (MPs) represent a pervasive class of emerging environmental contaminants with demonstrated capacity for plant uptake through multiple entry pathways, particularly via soil-water-plant systems. Their phytoaccumulation has been shown to interfere with essential physiological mechanisms. In a controlled experiment, this study investigated the impact of polyvinyl chloride microplastics (PVC-MPs) on the growth and physiological-biochemical responses of Brassica chinensis L. seedlings. Different concentrations of PVC-MPs (0%, 0.5%, and 2% w/w) were introduced into the soil to assess dose-dependent effects on plant development. Results The results revealed a clear concentration-dependent response of B . chinensis to PVC-MPs exposure. At the lower concentration (0.5% w/w), PVC-MPs exerted a promoting effect, with increases in biomass accumulation, enhanced shoot elongation, and elevated foliar chlorophyll content. Conversely, higher concentration exposure (2% w/w) induced significant phytotoxic effects, where plant height was initially stimulated but inhibited subsequently, while leaf proline was accumulated for osmoregulation, accompanied by a pronounced reduction in stem starch reserves. Conclusion The results revealed distinct concentration-dependent mechanisms underlying the effects of PVC-MPs on plant growth. At lower concentrations, PVC-MPs stimulated plant growth through root morphological adjustment, where lateral root proliferation could improve efficiency of water and nutrient uptake. The root modification was also associated with enhanced assimilation, leading to greater shoot elongation and biomass accumulation. In contrast, higher-concentration PVC-MPs triggered growth suppression via inhibitory pathways: chloroplast damage compromised photosynthetic performance, while starch was conversed to soluble sugar as a osmoregulatory response. These coordinated physiological responses ultimately resulted in growth inhibition under high PVC-MPs exposure. Clinical trial number Not applicable.