Biodegradable microplastics coupled with biochar enhance Cd chelation and reduce Cd accumulation in Chinese cabbage

Abstract The impact of microplastics on the remediation of cadmium-contaminated soil by biochar is still unclear. Therefore, in the present study, we investigated the effects of combining different biochars with polylactic acid (PLA) microplastics on the growth of Chinese cabbage, rhizosphere soil metabolomics, bacterial community structure, and Cd accumulation in Cd-contaminated soil. Compared with the treatment with biochar alone, the addition of PLA suppressed plant growth, but also reduced Cd accumulation in Chinese cabbage by 8–42%; the treatment with sugarcane bagasse biochar (SBC)–PLA showed the most prominent effect. Compared with the treatment with SBC alone, SBC–PLA reduced Cd accumulation in roots and aboveground parts by 47 and 22%, respectively ( p < 0.05). The addition of PLA enhanced the soil organic matter, dissolved organic carbon, and total nitrogen contents, but reduced the available phosphorus and readily available potassium contents, with no significant impact on available Cd. The rhizosphere metabolite analysis showed that PLA plus biochar promoted the formation of cyclohexene terpenoids and chelating agents, the urea cycle, and chelation with Cd ions, thereby reducing Cd uptake by Chinese cabbage roots. The microbial structure analysis demonstrated that PLA plus biochar drove chelation between organic carbon, nitrogen, and Cd. This study highlights the potential of microplastics for mitigating Cd accumulation in plants and the remediation of heavy metal-contaminated soil. Graphical Abstract