Effect of polyethylene microplastics on physiological responses and vanadium accumulation in pakchoi (Brassica rapa subsp. chinensis) under vanadium stress

Vanadium (V) contamination poses potential risks to plant growth, while microplastics (MPs) may alter the behavior and bioavailability of heavy metals in soil. This study investigated the effects of polyethylene microplastics (PE) on the physiological responses and V accumulation of pakchoi ( Brassica rapa subsp. chinensis ) under V stress. A pot experiment was conducted with four PE concentrations (0, 0.1, 1, and 5%) under 150 mg·kg⁻¹ V. Growth traits, photosynthetic characteristics, antioxidant enzyme activities, malondialdehyde (MDA), soluble protein, V accumulation, and soil physicochemical properties were determined. V stress alone significantly inhibited pakchoi growth, reducing plant height, root length, and biomass by 60.26%, 70.11%, and 72.09%, respectively. It also decreased chlorophyll content and photosynthetic parameters, while increasing MDA content by 45.03%, indicating enhanced oxidative damage. Addition of 0.1% PE partially alleviated V toxicity by improving photosynthetic performance, reducing MDA content, and increasing superoxide dismutase (SOD) and peroxidase (POD) activities. However, the alleviating effect weakened at higher PE concentrations. PE addition also significantly decreased available V in soil and reduced V accumulation in pakchoi roots. These results indicate that low PE addition can mitigate V toxicity in pakchoi, likely by reducing V bioavailability in soil, whereas higher PE concentrations provide limited benefit.