Effects of top-pruning intensity on sprout regeneration, non-structural carbohydrate utilization, and root morphology in Pinus yunnanensis Franch. seedlings

This study aimed to investigate the effects of different top-pruning intensities on root morphology, non-structural carbohydrate (NSC) allocation, and sprout regeneration capacity of Pinus yunnanensis Franch . seedlings, and to reveal the underlying ecophysiological response mechanisms. Four top-pruning intensity treatments were applied to one-year-old P. yunnanensis seedlings: H1 (75% height removal), H2 (50% height removal), H3 (25% height removal), and CK (no pruning). Root morphological indicators, soluble sugar (SS) and starch (ST) contents in various organs, NSC allocation patterns, and sprout number and growth dynamics were measured in March, May, July, September, and November, respectively. Results showed that top-pruning significantly affected root architecture. The H1 treatment inhibited root growth in the early stage but gradually recovered in the later stage, while the H2 and H3 treatments promoted increases in total root length, root surface area, and root volume. NSC distribution across organs followed the order: stem > root > sprout > needle. Top-pruning promoted SS accumulation and accelerated the conversion of ST to SS. Sprout growth conformed to the Logistic model; top-pruning delayed the first sprouting peak to 90 days post-treatment, and the H2 treatment exhibited the optimal performance in terms of sprout number and growth. Structural Equation Modeling (SEM) revealed that top-pruning indirectly enhanced sprouting capacity by promoting SS accumulation and root development. In conclusion, P. yunnanensis seedlings respond to top-pruning disturbance by dynamically adjusting root morphology and NSC allocation strategies. Moderate top-pruning (H2) achieves the best performance in promoting sprout regeneration and resource use efficiency, providing a theoretical basis for the regeneration and management of P. yunnanensis plantations. • Top-pruning affected the changes of roots and sprouts. • Elucidates the "carbon economy" strategy in P. yunnanensis seedlings in response to top-pruning. • The correlation mechanism between sprout growth and energy flow.