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Effects of Nitrogen–Phosphorus Co-Application on Biomass Allocation and Accumulation in Two-Year-Old Pinus yunnanensis Seedlings
by
,
Jianzhen Liao
1,2, 
Yaqi Li
1,2,
Boning Yang
1,2,
Chiyu Zhou
1,2,
Zixing Pan
1,2,
Lin Chen
1,2,
Nianhui Cai
1,2 and
Yulan Xu
1,2,* 1
Key Laboratory of Forest Resources Conservation and Utilization in the Southwest Mountains of China, Ministry of Education, Southwest Forestry University, Kunming 650224, China
2
Key Laboratory of National Forestry and Grassland Administration on Biodiversity Conservation in Southwest China, Southwest Forestry University, Kunming 650224, China
*
Author to whom correspondence should be addressed.
Biology 2025, 14(9), 1115; https://doi.org/10.3390/biology14091115
Submission received: 13 July 2025
/
Revised: 19 August 2025
/
Accepted: 21 August 2025
/
Published: 22 August 2025
(This article belongs to the Section Conservation Biology and Biodiversity)
Simple Summary
The Pinus yunnanensis is an important tree species in the southwestern region of China. Its seedlings grow slowly, which limits its benefits in terms of ecology and cost-effectiveness Our research tested the effects of nitrogen and phosphorus fertilizers on the growth of seedlings. We designed nine different combinations of nitrogen and phosphorus fertilizers, and measured the biomass of each organ three times after fertilization. The results showed that the fertilizers promoted the accumulation of biomass in each organ and also increased the allocation of biomass to the root. Among the nine treatments we set up, T5 (N: 0.5 g·plant−1, P: 0.8 g·plant−1) had the best effect on promoting biomass accumulation. Based on the optimal fertilizer requirements for biomass accumulation in each organ, the ideal fertilizer dosage is nitrogen 0.5–0.6 g·plant−1 and phosphorus 0.5–0.9 g·plant−1, with a nitrogen and phosphorus ratio of 1.0:0.8–1.0:1.8. These findings can help growers optimize their fertilization methods to accelerate the growth rate of seedlings, thereby promoting the healthy growth of forests and the livelihoods of local residents.
Abstract
Pinus yunnanensis is a significant native tree species in southwestern China, contributing substantially to the area’s ecological stability and economic growth. However, its growth rate tends to be relatively slow during the seedling stage, and fertilization is crucial to promote seedling growth. This study used two-year-old P. yunnanensis seedlings as experimental materials and applied a 3 × 3 factorial design, combining three nitrogen (N) levels (0, 0.4, and 0.8 g·plant−1) supplied in the form of urea with three levels of phosphorus (P) (0, 0.8, and 1.6 g·plant−1) supplied in the form of superphosphate to form nine treatments, denoted as T1 to T9. This study was carried out in the open-air nursery of Southwest Forestry University, with fertilization beginning in July and observations continuing until December of the same year. Using allometric growth analysis and constructing the fertilizer response regression equation, we investigated the effects of fertilization on biomass accumulation in P. yunnanensis. The findings revealed that fertilization significantly increased the biomass allocation ratio to roots but decreased the allocation to needles and aboveground parts (p < 0.05). Allometric growth analysis showed that root growth was more rapid than stem and needle growth, and the growth rate of belowground parts exceeded that of aboveground parts. Allometric growth between organs differed among treatments, whereas the allometric growth relationship between aboveground and belowground biomass showed no significant difference across treatments. Moderate N and P fertilizer application promoted biomass accumulation in all organs, with T5 (N: 0.4 g·plant−1; P: 0.8 g·plant−1) exhibiting the highest biomass accumulation. Based on the comprehensive analysis of optimal N and P fertilizer requirements for biomass accumulation across different organs, the recommended fertilizer application rates are as follows: N 0.5–0.6 g·plant−1 and P 0.5–0.9 g·plant−1, with an optimal N:P ratio ranging from 1:0.8 to 1:1.8. The results establish a scientific rationale for enhancing fertilization methods in P. yunnanensis seedling cultivation, contributing to the slow growth issue during the seedling stage.
