Triacontanol–biochar synergy regulates redox homeostasis and stress signaling in wheat under neodymium toxicity

Rare earth element contamination is an emerging environmental concern that disrupts plant physiological and signaling processes. This study investigated the role of triacontanol and rice stalk-derived biochar in modulating stress signaling and physiological responses in wheat (Triticum aestivum L.) exposed to neodymium (Nd) toxicity. Rice stalk biochar synthesized at 400 °C was characterized using FTIR and XRD analyses, confirming its crystalline structure and pseudospherical morphology with an average size of ~12 nm. Neodymium exposure markedly impaired plant growth, reducing root and shoot lengths by 59.68% and 55.02% and decreasing dry biomass by 40.02% and 50.20%, respectively. The combined application of triacontanol and biochar significantly mitigated these inhibitory effects, restoring root and shoot growth by 220.11% and 160.79% and improving dry biomass accumulation. This treatment also reduced Nd accumulation in roots and shoots by 37.30% and 33.19%, respectively. Importantly, the combined treatment enhanced photosynthetic pigment levels and photosynthetic efficiency, increased the relative water content (79.88%), and stimulated osmolyte accumulation, including glycine betaine (40.51%) and proline (19.87%). Furthermore, neodymium-induced oxidative stress was alleviated through reduced reactive oxygen species accumulation and the activation of antioxidant defense systems, including GR, APX, CAT, SOD, MDHAR, and DHAR enzymes. These findings suggest that triacontanol and biochar synergistically regulate physiological and antioxidant signaling networks, thereby enhancing wheat tolerance to rare earth element toxicity. The study highlights a sustainable strategy for mitigating metal-induced stress while providing insights into plant adaptive signaling mechanisms.