Effects of biochar on the growth, physiology and heavy metal uptake of Trifolium pratense L. in Pb-contaminated soil

Biochar is an inexpensive and effective material that can immobilize heavy metals. However, the impact of varying levels of biochar application on red clover cultivated in soil contaminated with Pb remains unclear. In this study, five different doses of biochar (0, 2.5, 5, 10, and 15%) were applied to soils containing two levels of Pb (LPb, 1000 mg/kg; HPb, 5000 mg/kg) to assess the growth, physiological characteristics, and heavy metal enrichment capacity of red clover. Pb stress dramatically slowed down plant development, decreased the amount of photosynthetic pigment, and caused oxidative damage, according to the results of pot tests. However, the addition of biochar mitigated Pb toxicity in red clover by effectively adsorbing Pb from soil and reducing Pb translocation to plant tissues. Specifically, red clover growth was significantly enhanced by the addition of 5% biochar to soil contaminated with either low- or high-level Pb. This resulted in an increase in plant biomass, stimulated the upregulation of LHCA1 and CCS genes, and facilitated the production of photosynthetic pigments. Furthermore, it increased antioxidant enzyme activity while reducing proline accumulation. This work offers a theoretical foundation for the remediation of Pb-contaminated soils using plants and biochar.