Objectives The seasonal changes of carbon (C), nitrogen (N), phosphorus (P) contents and their ecological stoichiometric characteristics in different organs of Pinus armandi young forest were studied, and the allometric growth relationship was analyzed to predict the possibility of nutrient limitation of young pine trees and improve the management.
Methods In order to analyze the C, N and P contents of P. armandii organs and their ecological stoichiometric changes in different seasons, samples of P. armandii needles, branches, stems, and roots were collected from the plantation of P. armandii in the Yiliang County State-Owned Garden Forest Farm, Kunming City, Yunnan Province, China, in January, May, August, and November of 2021, respectively.
Results 1) Sampling site, growing season and their interactions had significant (P<0.05) effects on C, N and P contents and their stoichiometric ratios.C and P contents and C∶P ratios were mainly affected by the growing season, while N, C∶N ratios and N∶P ratios were mainly affected by the sampling site. 2) The C content of each part in winter was significantly higher than that in other seasons. The N content of leaves and branches in winter was significantly higher than that in spring and summer, and the P content of leaves and stems in summer was significantly higher than that in autumn and winter. The C content of young pine trees was stem > branch > leaf > root, the N content was leaf > branch > root > stem, and the P content was root > leaf > branch > stem. When N : P < 14, it is considered that the growth and development of plants are more limited by N element. In this study, the N : P of each part is less than 14, indicating that the main limiting nutrient element for the growth of young P. armandii forest in the test area is N. 3) Needle N content had the largest plasticity index (0.79), followed by leaf P content (0.64), indicating that the nitrogen and phosphorus nutrients in the needles of young P. armandii forests were susceptible to external environmental influences. 4) The C-N of leaves, branches and stems showed a significant allometric relationship, reflecting the different distribution and regulation modes of C and N content in different parts of trees.
Conclusions The absorption of N and P elements in the needles of young P. armandii plantation is easily affected by the growth season. It is suggested that appropriate N and P fertilizers should be added in the management of the P. armandii plantation, especially the restrictive element N, so as to promote the growth.
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