Abstract: In order to establish the low temperature injury grades on Syzygiums amarangense, one year old Syzygiums amarangense graft seedlings (var. Black Pearl) were treated in the climate chamber for 1day, 2 days and 3 days respectively, where the daily minimum temperature (Tmin) were set at 2℃, 1℃, 0℃, ?1℃ and ?2℃, the diurnal temperature differences were set 15℃ (radiation temperature decrease) and 6℃ (temperature decrease with highly humidity). There were 10 treatments, and each treatment included 3 replicates. 3 plants was as CK in nature light in fields (photo flux density was 300～500μmol·m?2·s?1） under normal atmospheric temperature（daily average temperature was 15～20℃). Morphological changes of S. amarangense graft seedling were observed and recorded both immediately and 10 days after treatment. Those physiological and chemical index related stress were detected, such as soluble sugars, proline, soluble proteins, and MDA concentrations, SOD activity, relative electrical conduction in its leaves. The critical temperatures that injured the leaves and branches of S. amarangense graft seedling were preliminary analyzed. The cold injury indexes of S. amarangense seedling were established depending on the morphological changing, the physiological index variation with the Tmin changing and its durations. In order to verify and test the injury index that established with controlling conditions. Morphological changes of S. amarangense graft seedling were observed in different elevations and latitudes. The results showed that the injury critical temperature index obtained from controlled conditions were consistent to geographical displacement test. The low temperature injury index were divided into 5 grades, that were, (1)death, Tmin≤?2℃; (2)serious injury, ?2℃＜Tmin≤?1℃; (3)moderate injury, ?1℃＜Tmin≤2℃; (4)light injury, 2℃＜Tmin≤5℃, lasting for more 3 days the leaves of S. amarangense seedlings maybe fall off, and the following growth should be affected. The grades of death; (5)normal, Tmin＞5℃.

Key words: S. amarangense seedling, Low temperature injury grades, Morphological and physiological index;, Geographical displacement test, Artificial control test