Response of Photosynthetic Characteristics and Nutrients of Abies georgei var. smithii Needles to Altitudes

Abies georgei var. smithii from the Yulong Snow Mountain in Northwest Yunnan was selected to study the response of needle photosynthesis and nutrient accumulation to different altitudes. The results showed that the instantaneous maximum net photosynthetic rate (P_n), photosynthetic nitrogen utilization efficiency（PNUE）and long-term nitrogen use efficiency (NUE) reached the top value at the altitude of 3500 m. The δ¹³C value of needles decreased firstly and then increased with the increasing altitude, it reached the highest level at the altitude of 3700 m. On the other hand, the contents of C, N, P per unit needle area also increased to the maximum, while the stomatal conductance (G_s), transpiration rate (E), and intercellular CO₂ concentration (C_i) reduced to the lowest level at the altitude of 3700 m. The altitude of 3550 m is the most suitable growth area for A. georgei var. smithii. Although the altitude below 3550 m has no obvious negative effect on this tree species, the photosynthetic intensity, needle nutrient contents and nitrogen use efficiency just reached the middle levels. However, the altitude above 3550 m may restrict the growth and development of A. georgei var. smithii, but at the same time, it can adapt to the harsh environment of high altitude by adjusting the nutrient metabolism and improving the water use efficiency.