Potassium nutrition regulates growth, nutrient-carbon interactions and lignification during autumn in Tsoongiodendron...

Tsoongiodendron odorum is a precious tree species native to the subtropical region of southern China, valued for both timber production and ornamental purposes. However, the optimal potassium application rate for its seedlings during autumn and the underlying physiological response mechanisms remain unclear. In this study, one-year-old T. odorum seedlings were subjected to six potassium levels (25, 65, 105, 145, 185, and 225 mg·plant⁻¹) and a control (0 mg·plant⁻¹) to investigate the effects on seedling growth, carbohydrate content, and nutrient accumulation. The results showed that moderate potassium supply (65-105 mg·plant⁻¹) significantly promoted seedling growth and root development, with the 105 mg·plant⁻¹ treatment achieving maximum values for seedling height, basal diameter, biomass, and root traits. This treatment also optimized nutrient stoichiometric ratios (N:P, N:K, and K:P within balanced ranges), increased leaf soluble protein and non-structural carbohydrate contents, and enhanced stem lignin accumulation. Redundancy analysis (RDA) identified starch, total nitrogen, and soluble protein as the dominant factors influencing growth; partial least squares structural equation modeling (PLS-SEM) further revealed that potassium supply regulated seedling growth through both direct pathways and indirect pathways mediated by nutrient and carbohydrate status. In conclusion, autumn potassium application at 105 mg·plant⁻¹ effectively improves the quality of T. odorum seedlings, providing a theoretical basis and practical guidance for nutrient management in autumn nursery cultivation of this species.