PHYSIOLOGICAL INDEXES OF POPULUS EUPHRATICA LEAVES FROM DIFFERENT CANOPY POSITIONS IN THE LOWER REACHES OF TARIM RIVER

Populus euphratica have serious degeneration under the long-term stress in the lower reaches of Tarim River and many trees began to wither from upper canopy to lower canopy. In this paper, differences in physiological indexes of Populus euphratica leaves between upper canopy, middle canopy and lower canopy, which response to the external stress were studied. The results showed that the contents of water (RWC), soluble sugar (SS), free proline (Pro) and the activities of peroxidase (POD) decreased from lower canopy to upper canopy, while the content of malondialdehyde (MDA), the activities of superoxide dismutase (SOD) and the ratio of chlorophyll a and chlorophyll b (Chl a/b) increased. These results indicated that the external stress on the upper canopy was higher than the middle and lower canopy. That may be the main reason resulting in the death of the upper canopy. The contents of chlorophyll a (Chla), chlorophyll b (Chlb) and total chlorophyll (Chlt) were slightly higher in the middle canopy than in other canopies, indicating the ability of absorbing light was same in canopies. These findings from this study will contribute to the best management of Populus euphratica.