Objective This study aimed to evaluate the effectiveness and physiological safety of aquaculture pond sediments as a soil amendment for cultivating rare plant species, in order to provide a scientific basis for their resource utilization and cultivation management.

Method A pot experiment was conducted using aquaculture pond sediments collected from a rare and endemic fish conservation station jointly operated by the Xiluodu and Xiangjiaba hydropower projects along the Jinsha River, and native soil obtained from the Xiangxi Rare Plant Garden. Five sediment–soil mixtures were prepared: CK (0∶1), T1 (1∶2), T2 (1∶1), T3 (2∶1), and T4 (1∶0). Three nationally protected Class II species—Cinnamomum japonicum, Paradombeya sinensis, and Plantago fengdouensis—were selected as experimental species. The physicochemical properties of the substrates, plant growth traits, and key physiological indicators were measured.

Result Increasing proportions of aquaculture pond sediments significantly increased alkaline hydrolyzable nitrogen, available potassium, organic matter content, and electrical conductivity (EC) in the substrates. Compared with CK, T1 - T4 treatments increased alkaline hydrolyzable nitrogen by 213.24% - 643.93%, available potassium by 46.76% - 185.05%, organic matter content by 41.72% - 257.85%, and EC by 428.14% - 840.90%, resulting in a clear fertility gradient. Growth promotion was mainly observed during the mid-to-late stages of the experiment. In June, canopy width of C. japonicum increased by 16.31% - 27.39% under T2 - T4 treatments, and branch number increased by 58.01% - 279.23% under T1 - T4 treatments. In P. sinensis, canopy width and leaf area increased by 26.62% - 31.87% and 34.48% - 84.07% under T2 - T4 treatments, while basal stem diameter increased by 25.00% - 37.50% under T1 - T4 treatments. In P. fengdouensis, seed production increased by 23.89% - 35.63% under T2 - T4 treatments, while canopy width and leaf number increased by 41.24% and 48.01% under T4 treatment. Under most treatments, the concentrations of hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and secondary metabolites in leaves and roots did not show consistent changes, and no systematic oxidative stress responses were detected.

Conclusion Aquaculture pond sediments enhanced substrate fertility and promoted the mid- to late-stage growth of rare plant species while maintaining overall physiological safety. Considering both plant growth responses and changes in substrate physicochemical properties, a sediment-to-native soil ratio of 1∶1 to 2∶1 can be considered a relatively robust application range. Under pot conditions, the sediment-only treatment also exhibited significant growth-promoting potential.