Abstract: Introducing and breeding salt-tolerant plants are a main way to exploit saline land with an important research value. We used one-year seedlings of Betula kirghisorum, B.pendula, B.pubescens brought from Kazakhstan and local B.platyphylla Suk. as the test materials. Neutral salt(NaCl) and alkaline salts(NaHCO₃) stress tests were conducted in July 2014 in Northeast Forestry University. We measured growth, photosynthesis and chlorophyll content. We used factor analysis method to compare and evaluated the salt tolerance of four kinds of birch seedlings. At last, we screened the birch species with an excellent comprehensive performance. As the salt concentration increases, the high growth and photosynthetic efficiency of birch seedlings were significantly inhibited and while the concentration≥0.5%, most seedlings withered. Correlation of height and diameter-increment, net photosynthetic rate(P_n), photosynthetic-light-use efficiency(SUE), carboxylation efficiency(CUE), apparent quantum yield(AQY) and chlorophyll content reached a significant level. We obtained the following comprehensive evaluation formula for salt stress treatment of 0.1% NaCl, 0.3% NaCl, 0.1% NaHCO₃ and 0.3% NaHCO₃ and screened out the best individual plants with exceptional comprehensive characters. The optimum individual plants for NaCl stress were 32, 33, 34 and 35, and for NaHCO₃ stress were 262, 263, 264 and 35, respectively. B.kirghisorum had the strongest resistance to neutral salt and B.platyphylla Suk. had the strongest resistance to alkaline salt with low concentration, and B.kirghisorum and B.pubescens had more resistance to alkaline salt with high concentration.

Key words: birch, salt stress, salt tolerance, net photosynthetic rate, photosynthetic-light-use efficiency, arboxylation efficiency, factor analysis