Integrated physiological, biochemical, transcriptomic, and metabolomic analysis reveals the mechanism of silicon in alleviating cadmium stress in Juglans sigillata

Cadmium (Cd) pollution significantly reduces nut production and threatens human health. Silicon (Si) can mitigate heavy metal toxicity in plants. Juglans sigillata (J. sigillata) is highly nutritious and economically valuable for its wood; however, Cd strongly inhibits its growth. To investigate the beneficial effects of Si in alleviating Cd stress, four treatment groups were established: CK (H2O only), Si (Si only), Cd (Cd only), and CdSi (Cd and Si). The results showed that Cd accumulation in the roots, stems, and leaves decreased by 9 %, 46.1 %, and 41.6 %, respectively, in the CdSi treatment group compared to the Cd-only group, thereby reducing plant damage. Compared to Cd treatment alone, the CdSi group exhibited significant increases in the activities of superoxide dismutase, peroxidase, and catalase by 50.64 %, 118.35 %, and 9.83 %, respectively, along with an increase in proline content. These changes led to a 12.65 % reduction in malondialdehyde levels and 0.85-fold and 0.89-fold decreases in superoxide anion and hydrogen peroxide concentrations, respectively. High-throughput sequencing revealed the upregulation of Si transporters, zinc-iron transporters, heavy metal-associated isoprenylated plant proteins, and other ion homeostasis-related transporters. Genes involved in cell wall synthesis, such as caffeic acid 3-O-methyltransferase and xylose isomerase, along with metabolites including phenylpropanoids, galactose, and mannose, were also upregulated. In summary, Si promoted J. sigillata growth by enhancing cell wall function, maintaining ion homeostasis, increasing osmotic adjustment, and strengthening the antioxidant system. Therefore, this study elucidates the physiological, biochemical, and molecular mechanisms underlying Si-mediated alleviation of Cd stress in J. sigillata.