Objectives We studied the growth and the responses of carbon (C), nitrogen (N) and phosphorus (P) stoichiometric characteristics of Ochroma lagopus to nitrogen application rate, to provide a theoretical basis for the nutrient management of O. lagopus plantation.

Methods A field experiment was conducted with 2-year-old O. lagopus in the O. lagopus plantation forest of Mengxin Farm, Mengla County, Yunnan Province, using a randomized block group design, with seven treatments: no nitrogen control (CK) and application of urea and slow-release fertilizers of 300 g/plant (N1, H1), 450 g/plant (N2, H2), and 600 g/plant (N3, H3), and the time of fertilization was in June 2023, and samples were collected in October 2023, and the height and diameter at breast height of O. lagopus trees were determined, C, N, and P contents in leaves, branches, and roots were analyzed, and the stoichiometric eigenvalues of each organ were calculated.

Results Compared with CK, the increase in diameter at breast height was not significant in the low N rate (N1, H1) treatments and the increase in tree height was not significant in the N1 treatment, while the diameter at breast height and tree height was significantly higher in the medium and high N rate treatments (N2, N3, H2, H3) than in CK, but the differences among the four treatments were not significant. Nitrogen application had no significant effect on the C content of O. lagopus branches and roots, but N3 and H3 reduced the C content in leaves; N application significantly increased the N content in branches, leaves and roots, and the increase was significantly higher with the increase of N application. Nitrogen application significantly decreased the P content in leaves, and the rate of decrease increased significantly with the increase of N application, but the leaf P content of H1 treatment was significantly lower than that of N1, while there was no significant difference between H2 and N2, and between H3 and N3; N3 and H3 decreased the P content in branches. Nitrogen application increased root P content, and the increase increased significantly with the increase of N application, and the root P content of N3 was significantly higher than that of N1, and the root P content of the three sulfur-coated slow-release fertilizer treatments had no significant difference. Under CK treatment, the leaf N:P is less than 14, and the growth of O. lagopus was limited by N. Under medium and high nitrogen addition treatments, leaf N:P was greater than 16, and the growth of O. lagopus was changed from being limited by N to being limited by P. Leaf N:P in H2 and H3 treatments was significantly higher than that in N2 and N3, which meant that the phosphorus limitation brought by the application of sulfur-coated slow-release fertilizer was greater than that of urea. Correlation analysis showed that the growth of O. lagopus was significantly correlated with the nutrient content and stoichiometric characteristics of each organ, and the growth of O. lagopus was significantly affected by the nitrogen content of each organ. The results of phenotypic plasticity and principal component analysis showed that the phenotypic plasticity indices of O. lagopus growth, C, N, P content of each organ and stoichiometric characteristics under nitrogen addition ranged from 0.05 to 0.52, and the cumulative ANOVA contribution of principal component 1 and principal component 2 was 63.2%; O. lagopus adapts to the external changes under nitrogen addition mainly by regulating the N and P content of each organ, and then promotes the growth of O. lagopus.

Conclusions Nitrogen addition has a significant effect on the growth of O. lagopus plantation forests and the stoichiometric characteristics of C, N and P in each organ. The application of medium- and high-rate nitrogen fertilizers is more effective than low rate nitrogen fertilizers in improving the growth of O. lagopus and easing the restriction of nitrogen on the growth of O. lagopus, but it affects the distribution of C, N and P in various organs, and it also causes phosphorus restriction, and the phosphorus restriction brought about by sulfur-coated slow-release fertilizers is even more severe. Therefore, in the production management of O. lagopus plantation forests, attention should be paid to the application of nitrogen fertilizer, and when applying sulfur-coated slow-release fertilizers, special attention should be paid to supplementing phosphorus fertilizer.