Abstract: Polyvinyl chloride (PVC) microplastics are commonly found in greenhouse soils. They are highly phytotoxic and pose a serious threat to plant growth and development. Therefore, measures to reduce the phytotoxicity of PVC microplastics are urgently needed. Biochar is known for its strong adsorption capacity. It can effectively passivate soil contaminants and has been widely used in the remediation of soil contamination. Additionally, biochar has exhibited great application potential for improving soil quality and increasing crop yields. To determine the effect of biochar on PVC microplastic phytotoxicity in greenhouse soils, the growth, physiological and with biochemical indices of lettuce (Lactuca sativa) were analyzed under single exposure to PVC microplastics and combined exposure to PVC microplastics and with biochar at different concentrations. The results show that the chlorophyll content of lettuce leaves exposed to single PVC microplastics was significantly increased compared to the control group (P<0.01). However, the biomass of root and shoot of lettuce was reduced by 23.54% and 12.04%, respectively. This may be attributed to the adhesion of PVC microplastics to the surface of lettuce roots, which induced the production and accumulation of hydrogen peroxide (H₂O₂) in the roots and caused oxidative damage, thus affecting the normal physiological function of the roots. The addition of 0.5% to 2.5% biochar to the PVC microplastics-contaminated soil resulted in a decrease in malondialdehyde (MDA) levels in lettuce roots and leaves and an increase in lettuce biomass compared to the single PVC microplastics exposure treatment group. However, the high concentration (5.0%) of biochar exacerbated the oxidative damage to lettuce roots and attenuated its growth-promoting effect on lettuce. These results suggest that the phytotoxicity of soil microplastics can be mitigated by the addition of appropriate amounts of biochar, and can provide a scientific basis for addressing soil microplastic pollution in agriculture.

Key words: microplastics, greenhouse soil, lettuce, phytotoxicity, oxidative stress