Abstract: We investigated the effectiveness of photosynthetic characteristics as an evaluation index of salt tolerance in five trees differing in tolerance to salt stress. The salt tolerance rank of the five trees is Lycium dasystemum>Ulmus pumila>Celastrus orbiculatus>Syringa microphylla>Pinus sylvestris var. mongolica. Five woody plants responsed identically to NaHCO₃ stress, that is, net photosynthetic rate (P_n), transpiration rate (T_r), stomatal conductance (G_s), intercellular space CO₂ concentration (C_i) and stomata limitation (L_s) all decline obviously. P_n decreasing scale of five trees was P.sylvestris var. mongolica>S.microphylla>C.orbiculatus>U.pumila>L.dasystemum. T_r decreasing scale of five trees was P.sylvestris var. mongolica>S.microphylla>L.dasystemum>C.orbiculatus>U.pumila. G_s decreasing scale of five trees was P.sylvestris var. mongolica>L.dasystemum>Ulmus pumila>S.microphylla>C.orbiculatus. According to the changes of photosynthesis parameters of five seedlings, under lower stress intensity, the main factor leading to decreasing in photosynthesis rate of U.pumila and L.dasystemum was stomatal limitation, while there was non-stomatal limitation under higher stress intensity. The main factor leading to decreasing in photosynthesis rate of C.orbiculatus and P.sylvestris var. mongolica was stomatal limitation. Non-stomatal limitation was the main factor leading to decreasing in photosynthesis rate of S.microphylla. The more salt-tolerant U.pumila and L.dasystemum had a less decreasing scale of photosynthesis rate than that of S.microphylla and P.sylvestris var. mongolica.

Key words: woody plant, NaHCO₃ stress, photosynthesis, physiological response