Abstract: The aim of this study was to examine the allometric relationships among nutrient elements including nitrogen (N), phosphorus (P), potassium (K) contents and their stoichiometric ratios (N∶P, N∶K, P∶K) and the size of two-years-old Pinus yunnanensis seedlings. Biomass of root, stem, needle and individual plant, and the contents of N, P, K were measured. The relationships were analyzed and the fitting models were built between biomass and nutrient element contents and stoichiometric ratios. The results showed that N, P, K contents were characterized by needle>stem>root, and that the nutrient contents of all organs and individual plant were characterized by K>N>P. The stoichiometric ratios differed among organs. We found higher N∶P and N∶K in needle, lower N∶P and N∶K in root, higher P∶K in root, and middle N∶P and N∶K in stem. P∶K in stem and needle was similar. There were significant positive correlations between biomass and nutrient contents in root, stem, needle and individual plant (P<0.01). Nutrient contents increased with increasing seedling size (biomass). There were negative correlations between N∶P ratios and biomass in root, stem, needle and individual plant. There were positive correlations between P∶K ratios and biomass in root, stem, needle and individual plant. The relationships between N∶K and biomass were different in root, stem, needle and individual plant. N∶K was negatively correlated with biomass in needle and individual plant, but positively correlated with biomass in root and stem. The fitting models were constructed between nutrient contents and biomass, and between stoichiometric ratios and biomass. Our results revealed that the characteristics of N, P, K contents and seedling size, and the allometric relationships between stoichiometric ratios and seedling size of P. yunnanensis seedlings.

Key words: C∶N∶P, nutrient element, biomass, allometric growth