Objectives Parashorea chinensis (a Grade Ⅰ nationally protected wild plant in China) faces challenges in population regeneration due to slow seedling growth, low lignification, and poor survival rates during autumn and winter. Potassium (K), a key nutrient for plant growth and lignification, was applied in autumn to investigate its dose-response effects on seedling growth, nutrient absorption, storage, lignification, and substrate nutrient status, aiming to optimize nutrient management for improving seedling quality.

Methods A pot experiment was conducted using 4-month-old seedlings of two Parashorea chinensis provenances, Napo and Tianyang. The substrate consisted of yellow soil and rice husks mixed at a 2∶1 (v/v) ratio. Treatments included three controls: no fertilizer (CK-1), K-only (K 160 mg/plant, CK-2), and N-P fertilization (N 200 mg/plant + P 80 mg/plant, CK-3). Five K levels (K 40, K 80, K 160, K 320, K 640 mg/plant) were applied alongside CK-3. After one year, growth parameters (height, ground diameter), biomass, lignification indicators (lignin and cellulose content, PAL activity), plant nutrient content, and substrate available nutrients were measured.

Results 1) Seedling growth and biomass: height, ground diameter, and total biomass of both provenances increased initially and then decreased with increasing K application, peaking at K 160 mg/plant. 2) Lignification: Cellulose content and phenylalanine ammonia-lyase (PAL) activity peaked at K 160 mg/plant for both provenances. Lignin content peaked at K 80 mg/plant for Napo and K 160 mg/plant for Tianyang. 3) Nutrient dynamics: Total plant N and P content, and N-P-K accumulation peaked at 160 mg K/plant, while K content reached its maximum at K 640 mg/plant. Root N-P-K allocation under K treatments was significantly lower than CK-1. Stem allocation initially increased then decreased, whereas leaf allocation showed an initial decline followed by an increase with rising K application. N and P use efficiency first decreased then increased, whereas K use efficiency gradually declined. 4) Nutrient stoichiometry: N/P in roots, stems, and leaves first rose then fell; N/K decreased and K/P increased with higher K application. Root and stem N/K ratios >2.1 indicated no K limitation, but leaf N/K >2.1 coupled with K/P <3.4 under treatments with K ≤ 320 mg/plant suggested K limitation in leaves. All treatments exhibited N/P <14, indicating N limitation. 5) Substrate nutrients: ammonium-N, available P, and available K first decreased then increased, while nitrate-N fluctuated minimally.

Conclusions Autumn K application at 160 mg/plant combined with N-P fertilization significantly enhanced seedling growth, lignification, nutrient accumulation, and substrate nutrient status in both provenances. Although no significant differences in height, ground diameter, or total biomass were observed between Napo and Tianyang provenances, Napo exhibited superior lignification, nutrient utilization, and allocation efficiency. The optimal K application rate was identified as 160 mg/plant under the given N-P fertilization regime.