Abstract: This paper studied the effects of foliar spraying spermidine and sperm ine on the leaf antioxidant system of Celastrus orbiculatus under soil NaHCO 3 stress. The results showed that under the stress, spraying spermidine and sp ermine could significantly decrease the leaf O2〖SX(B-*3〗-〖〗·〖SX)〗 production rate, H2O2 and MDA contents, and electrolyte leakage of C. orbiculatus (P<005). Spra ying spermidine increased the leaf SOD, CAT, POD and APX activities and GSH, CAR and Pro contents obviously, but had no effect on leaf AsA content. Spraying sp ermine also increased leaf POD and APX activities and GSH, CAR and Pro contents obviously, but had lesser effect on leaf SOD activity and AsA content, and even , caused a significant decrease in leaf CAT activity. In the meantime, spermidin e and spermine effectively improved the growth of C. orbiculatus seedlings. It was suggested that under soil NaHCO3 stress, exogenous spermidine and sperm ine could improve the functions of membrane protective system and decrease the O 2〖SX(B-*3〗-〖〗·〖SX)〗 accumulation in C. orbiculatus leaves, an d consequently, increase the C. orbiculatus tolerance to NaHCO3 exposure.

Key words: inhalable particulate matter, fine particulate matter, composition, source, forest.