Biomass allocation and allometric growth analysis of Pinus yunnanensis under different mixed nitrogen and phosphorus fertilization conditions

Abstract

Based on the hypothesis of nutrient balance and the theory of allometric growth, this study investigated the biomass allocation pattern and its allometric growth relationship of one-year Pinus yunnanensis Franch seedlings through the experiments of nitrogen (N) and phosphorus (P) dosing and application. The experimental design adopted a 3 × 3 full factorial design with two factors and three levels. The three levels of the two factors (N and P) were each combined in pairs, resulting in a total of 9 treatments. Results showed that, in comparison to the control (T1), the biomass accumulation and allocation patterns of Pinus yunnanensis seedlings were significantly different (P < 0.05) in different treatments. In general, regarding the biomass accumulation in the root, stem, and leaf of Pinus yunnanensis, the effects of different treatments presented as follows: combined nitrogen and phosphorus treatment > single phosphorus treatment > single nitrogen treatment. In addition, it can be concluded from allometric growth analysis that the linear fitting effect of aboveground biomass is the best, followed by leaf. The linear fitting effect of root biomass was not obvious. The 3D surface plot analysis demonstrates that with increasing time, the model fit improved significantly, indicating a time-dependent cumulative effect of fertilization. Correlation analysis revealed differential organ-nutrient relationships across treatments: nitrogen showed stronger associations with root and stem biomass, whereas phosphorus and nitrogen-phosphorus interaction were more closely related to leaf biomass. The findings revealed that amendment with nitrogen and phosphorus remarkably enhanced the biomass of Pinus yunnanensis. When compared, the combined application of nitrogen and phosphorus proved to be more advantageous than the single application of either nutrient, particularly in T5 (0.4 g N/plant + 3 g P/plant). Optimizing the nitrogen and phosphorus ratio in fertilizer has the potential to promote the growth of Pinus yunnanensis seedlings.