Abstract: Malus sieversii is a relic and rare wild fruit tree species from tertiary, and is the ancestor of cultivated apple trees in the world. In order to understand the nutrient stoichiometric characteristics of differentiation of M.sieversii, a total of 20 plots were investigated in 2016 and 2017 in mountainous area of west Junggar Basin, Xinjiang, China. The current-year stems of M.sieversii were collected, and the stoichiometric characteristics of nitrogen(N), phosphorus(P) and potassium(K) in stems, the differences in environmental gradients and the influencing factors were systematically analyzed. The N, P, K contents and N:P(7.03, 1.24, 5.96 mg·g^-1 and 5.71, respectively) in stems in 2016 were higher than those in 2017(5.49, 1.08, 4.46 mg·g^-1 and 5.13, respectively). Stem P had the lowest variability(CV=21.0% and 23.3%) while stem N had the strongest variability(CV=37.5% and 34.9%). There were significant correlations among stem N, P and K. Stem N:P, N:K were mainly influenced by N, while stem P:K were affected by K. ANOVA showed that significant differences in stem nutrient stoichiometry were detected among different years, sampling sites, degrees of altitude, grazing gradients, degrees of disease and insect pest, deadwood rates and fruit amounts. At the sampling plot level, longitude and latitude, slope position, grazing intensity and soil N content were the main factors affecting stem stoichiometry; at the individual plant level, the degree of diseases and insect pests and fruit amount were the key factors. When the in situ rejuvenation of M.sieversii is carried out, the moderate grazing, increasing soil N content and management of diseases and insect pests should be well considered.

Key words: Malus sieversii, current-year stem, stoichiomtery, environmental impact, degradation