Vermicompost-derived biochar alleviates nickel toxicity and bioaccumulation in wheat (Triticum aestivum L.) by improving soil properties and physiological functions

Abstract

Heavy metals (HMs) toxicity, such as nickel (Ni), has significantly reduced crop productivity and threatens human health, while efficient and widely applicable mitigation techniques remain underexplored. Vermicompost is an effective organic amendment to improve soil fertility and increase crop growth under HMs contamination; however, its derived biochar has not been extensively used to remediate Ni phytotoxicity. Hence, this study evaluated the ability of vermicompost (VC) and its derived biochar (VCB) in restricting nickel (Ni) bioaccumulation and growth improvement of wheat.The Ni toxicity decreased plant growth, physiological functions, and antioxidant capacity, along with yield parameters. Moreover, soil DTPA extractable Ni, Ni concentration in root and shoot and bioaccumulation factors significantly increase in Ni-contaminated soil (100 and 200 mg Ni kg⁻¹) compared with control (0 mg Ni kg⁻¹) soil. In contrast, the application of VC and VCB to soils containing 100 and 200 mg Ni kg⁻¹ significantly increased dry biomass (17%–25%), chlorophyll a and b (24%–43%), carotenoids (15%–30%), root volume (17%–35%), and 100-grain yield (15%–29%) compared with their corresponding Ni-only treatments. Among VC and VCB, VCB showed more prominent results in decreasing proline (12%) and H₂O₂ (44%) contents and enhancing CAT (45%) and POD (53%) activities under both 100 and 200 mg Ni kg⁻¹ levels, along with improving soil chemical properties and significantly increasing soil fertility. Further, the VCB application to Ni contaminated soils (100 and 200 mg Kg⁻¹) has significantly decreased soil-DTPA extractable Ni (59% and 44%), root and shoot Ni contents (56%, 65%, 56% and 53%), bioaccumulation factor (8% and 16%), respectively, compared with their corresponding Ni-only treatments. The VCB demonstrated a lower reduction in Ni translocation under Ni1 levels, whereas a significant reduction was found under Ni2 stress. The heatmap correlation and biplot PCA analysis confirmed that VC and VCB, particularly VCB, decreased soil and plant Ni, oxidative stress indicators, and metal accumulation factors and promoted growth, photosynthetic pigments and antioxidant variables through improved soil fertility compared to un-amended soil. This study provides a scientific basis and a practical solution for managing Ni-contaminated soils under diverse agroclimate conditions.