Abstract: With two-year old seedlings of Hippophea rhamnoides and Shepherdia argentea as test materials, this paper studied their growth and photosynthetic characteristics under the stress of different concentration (0, 200, 400 and 600 mmol·L-1) NaCl. The results showed that the biomass and total leaf area per plant of H. rhamnoides and S. argentea seedlings decreased significantly with increasing NaCl concentration. Comparing with the control, the root/shoot ratio of H. rhamnoides and S. argentea seedlings under NaCl stress increased obviously, while the leaf mass per area (LMA) decreased slightly. When the NaCl concentration increased and the stress time prolonged, the net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) of H. rhamnoides and S. argentea seedlings declined markedly, the intercellular CO2 concentration (Ci) increased after an initial decrease, whereas the water use efficiency (WUE) and stomatal limiting value (Ls) decreased after an initial increase. The dynamic changes of Gs, Ci and Ls indicated that the decline of Pn was mainly caused by the stomatal limitation in a short-term stress, and by non-stomatal limitation in a long-term stress. The poorer the salt tolerance of tree species and the higher the NaCl concentration, the earlier the transition from stomatal limitation to non-stomatal limitation would occur. As for H. rhamnoides, its morphological symptoms of salt injury appeared on the 10th day, and all of its seedlings were died on the 22th day under 600 mmol NaCl·L-1 stress. In contrast, S. argentea could tolerate 600 mmol NaCl·L-1 stress for above 30 days, illustrating that S. argentea, as an introduced tree species, had higher salt tolerance than H. rhamnoides, and could be planted widely in saline regions of China.

Key words: stubble-standing, wheat/maize intercropping, grain yield, water use efficiency.