Potassium supply coordinated nutrient accumulation, carbohydrate allocation and lignification of Tsoongiodendron odorum during autumn acclimation

Autumn represents a critical physiological stage for evergreen broad-leaved species, marking the transition from active growth to nutrient storage and tissue lignification. Potassium (K) is essential for nutrient balance, carbohydrate metabolism, and structural reinforcement in plants, but its role in autumn acclimation of evergreen woody species is poorly characterized. In this study, we investigated how a gradient of K supply affected nutrient stoichiometry, carbohydrate allocation, and lignification in seedlings of Tsoongiodendron odorum during autumn growth. Increasing K availability enhanced root activity and nutrient acquisition, resulting in changes in the proportion of N, P and K in roots, stems and leaves. Moderate K supply optimized nutrient stoichiometry and promoted the accumulation of non-structural carbohydrates, particularly soluble sugars and starch, which serve as precursors and metabolic resources for cell-wall biosynthesis. Consistently, lignin content and stem thickening were substantially increased under adequate K supply, indicating enhanced structural reinforcement as a physiological strategy for overwintering. Partial least squares structural equation modeling (PLS-SEM) demonstrated that the effects of K on lignification were mediated by coordinated nutrient–carbon regulation rather than by nutrient concentration alone. Consequently, in this study, autumn application of 105 mg·plant⁻¹ K optimizes growth of Tsoongiodendron odorum seedling, nutrient and carbohydrate reserves, and stem lignification, thereby improved seedling quality and overwintering potential. This study provides new insights into the role of K nutrition in the autumn acclimation of evergreen tree species, highlighting K as a key regulator of nutrient–carbon interactions, and offers a theoretical basis for precision nutrient management in subtropical nurseries.