In-situ remediation of heavy-metal-contaminated soil in farmland using phytostabilization combined with soil amendments is a low-cost and effective technology for soil pollution remediation. In this study, coconut shell biochar (CB, 0.1% and 0.5%), organic fertilizer (OF, 3.0%), and Fe-Si-Ca material (IS, 3.0%) were used to enhance the phytostabilization effect of ramie (Boehmeria nivea L.) on Cd and Pb in highly polluted soils collected at Dabaoshan (DB) and Yangshuo (YS) mine sites. Results showed that simultaneous application of CB, OF, and IS amendments (0.1% CB + 3.0% OF + 3.0% IS and 0.5% CB + 3.0% OF + 3.0% IS, DB-T5 and DB-T6) could significantly increase soil pH, reduce the concentrations of CaCl2-extractable Cd and Pb, and increase the contents of Ca, P, S, and Si in DB soil. Under these two treatments, the growth of ramie was significantly improved, its photosynthesis was enhanced, and its levels of Cd and Pb were reduced, in comparison with the control (DB-CK). After applying DB-T5 and DB-T6, the concentrations of Cd and Pb in roots were decreased by 97.7–100% and 64.6–77.9%, while in shoots they were decreased by up to 100% and 92.9–100%, respectively. In YS-T4 (0.5% CB + 3.0% OF), the concentrations of Cd and Pb in roots were decreased by 39.5% and 46.0%, and in shoots they were decreased by 44.7% and 88.3%. We posit that phytostabilization using ramie and amendments could reduce the Cd and Pb bioavailability in the soil mainly through rhizosphere immobilization and plant absorption. In summary, this study suggests that the use of tolerant plant ramie and simultaneous application of coconut shell biochar, organic fertilizer, and Fe-Si-Ca materials is an effective stabilization strategy that can reduce Cd and Pb availabilities in soil. Ultimately, this strategy may reduce the exposure risk of crops to heavy metal pollution in farmland.

To cope with heavy metal stress, plant root systems undergo root structure modification and release of multifarious metabolites. Elucidation of the resistance strategies to heavy metals mediated by the root system is crucial to comprehend the resistance mechanisms of plants. Here two rice cultivars with contrasting grain cadmium (Cd) accumulation traits were selected and the responses of their root systems to Cd stress were evaluated by morphological and metabolomics analysis. The phenomic and metabolomic responses of the root system varied between the two cultivars under Cd stress. The low-Cd accumulation rice cultivar (TY816) had a more highly developed root system that coped with Cd stress (10 μM) by maintaining high root activity, while the root cells of the high-Cd accumulation cultivar (JY841) lost viability due to excessive Cd accumulation. TY816 upregulated lipids and fatty acids to reduce Cd uptake, whereas JY841 upregulated phenylethanoid glycosides to cope with Cd-induced oxidative stress. The combination of metabolomics and phenomics revealed that rice roots employ multiple strategies to increase their tolerance of Cd-induced oxidative stress. Differing capacities to shape the root system architecture and reprogram root exudate metabolites may contribute to the contrasting Cd accumulation abilities between JY841 and TY816.