Nitrogen and Phosphorus Co-Fertilization Affects <i>Pinus yunnanensis</i> Seedling Distribution of Non-Structural Carbohydrates in Different Organs After Coppicing

The effects of nutritional additions on the non-structural carbohydrates (NSCs) of <i>Pinus yunnanensis</i> Franch. following coppicing were examined in this work. Three levels of phosphorous (P) addition, namely P₀ (0 g/plant), P (2 g/plant), and P+ (4 g/plant), and two levels of nitrogen (N) additions, namely N0 (0 g/plant) and N+ (0.6 g/plant) The treatments consisted of D1 (N₀P), D2 (N+P₀), D3 (N₀P), D4 (N+P), D5 (N₀P), and D6 (N+P+), utilizing an orthogonal design to assess how these nutrients influence NSC levels and their components throughout many plant organs in <i>P. yunnanensis</i>. The findings showed that fertilization enhanced NSCs and their components’ contents in <i>P. yunnanensis</i>. P treatment greatly raised NSC levels in sprouts as well as starch (ST) content in stems and sprouts. N treatment greatly raised soluble sugar (SS) and NSC content in stems and greatly accelerated the contents of NSCs and their components in sprouts. The combined application of N and P further improved SS content in stems. Fertilization effects varied over time, with significant increases in NSC content observed at different stages: at 0 d, fertilization significantly raised NSCs and their components in needles; at 90 d, roots and stems showed increases in both NSCs and their components’ contents; at 180 d, stem ST content significantly increased; and at 270 d, NSCs and their components’ contents across all organs were significantly increased. Especially in roots, stems, and sprouts, the combined N (0.6 g/plant) and P (2.0 g/plant) treatment (D4) produced the highest NSC concentration among the treatments. This suggested that NSC formation in plants might be greatly promoted by a balanced N and P fertilization ratio acting in concert. Moreover, fertilizer, as part of a general management plan, has long-term and significant benefits on plant development, especially after coppicing, accelerating recovery, expanding growth potential, and thereby strengthening the plant’s capacity to adapt to environmental changes.