Abstract: Pittosporum pentandrum and Koelreuteria elegans, native to Taiwan Island, exhibit strong abilities of wind and salt tolerance. Although the field trials have proved their adaptation to the stressful environments of coastal zone, little information is available to understand their measures of salt tolerance. In the current study, the effects of salt stress on the growth and antioxidant metabolism of oneyear old seedlings of P. pentandrum and K. elegans were studied under NaCl concentrations of 6, 9, 12 and 15 g·kg^-1. The results showed that, (1) The height and biomass of P. pentandrum and K. elegans seedlings decreased with the increase of NaCl concentration. Meanwhile, the root/shoot ratio increased for P. pentandrum, while decreased firstly and then increased for K. elegans. (2) The tolerance threshold values of P. pentandrum and K. elegans to NaCl concentration were 8.8 and 6.6 g·kg^-1, respectively. (3) The MDA content in each of the two species increased under high salt stress, but was higher in K. elegans than in P. pentandrum. (4) SOD, APX and GR activities of P. pentandrum leaves under NaCl stress were higher than those of K. elegans leaves. (5) Proline and soluble protein contents of P. pentandrum leaves were higher than those of K. elegans leaves and they both increased significantly under NaCl stress. The above results indicated that the saltadaptation mechanisms of P. pentandrum and K. elegans were different, and P. pentandrum and K. elegans were saltresistance and saltavoidance species, respectively. The salttolerance ability of former was stronger than that of latter. The stronger salttolerance ability of P. pentandrum may be related to its stronger antioxidant enzyme system and higher capability to accumulate proline and soluble protein under salt stress.

Key words: open-path infrared gas analyzer, fine-wire thermocouple, Burba correction, surface heating effect, optical path temperature