Abstract: Ecological stoichiometry is effective in studying the relationships between species and their environment. There are knowledge gaps in understanding the allocation of nitrogen (N), phosphorus (P), and potassium (K) in different organs, and how this allocation changes with age. Samples of roots, stems, and leaves of Picea schrenkiana at different growth stages were collected from the northern slope of Tianshan Mountains. N, P, and K concentrations were mea sured to analyze the stoichiometry at different growth stages, with the aim to examine allocation strategy and allometric relationship. The results showed that: (1) The allocations for N, P, and K among different organs were in the order of leaf > stem > root. With increasing age, the N, P, and K concentrations in leaves first increased and then decreased; N and K concentrations in stems increased gradually; N concentration in roots decreased, whereas P and K concentrations showed a gradual increase. (2) The stoichiometric ratios in different organs were 20.25-27.61 for N∶P,0.28-0.41 for N∶K, and 0.01-0.02 for P∶K. With increasing age, N∶P, N∶K, and P∶K in leaves and stems first increased and then decreased; N∶P and N∶K in roots decreased, and P∶K ratio showed no obvious pattern. Organ type, forest age and their interaction had significant effects on N, P, and K stoichiometry. (3) The proportions of N, P, and K contents allocated in different organs were following the order of stem > root > leaf. The N, P, and K concentrations in leaves, and N and K concentrations in stems and roots showed significant allometric relationships (leaves: N-P^0.956,P=0.001; N-K^-0.254, P<0.001; P-K^-1.568,P<0.001; stems: N-K^-0.326, P=0.011; roots: N-K^-0.529,P=0.007). Our results suggested that the N, P, and K stoichiometry of the organs changed at different growth stages as affected by environmental factors and the nutrient absorption and allocation.

Key words: carbon use efficiency (NPP/GPP), gross primary productivity (GPP), net primary productivity (NPP), northeast forest.