Abstract: Taking the Populus euphratica distributed in the lower reaches of Tarim River as an study sample, the relationship between proline content of Populus euphratica and different groundwater levels is particularly analysed at Yinsu and Aragan sectiones in this paper.The result shows that the relationship between proline content of Populus euphratica and different groundwater level at Yinsu section is consistent with that at Aragan section,namely while groundwater level drops,the proline content of Populus euphratica will increase;maybe two factors bring about the result.One is that there is positive relativity between proline content and degree of water stress.The other is that groundwater is most pivotal water source for growth of Populus euphratica at lower reaches of Tarim River.The result also shows that there is difference in increased extent of proline content of Populus euphratica under different ground water levels condition.Proline content in Populus euphratica body will accumulate along with aggravation of drought stress,which is feedback for Populus euphratica to adapt to drought adversity and is manner for Populus euphratica to resist drought and maintain itself normal life activity. Accumulation of praline is in favor of resist-drought ability of Populus euphratica when it suffers drought stress. The conclusion shows that growth of Populus euphratica already has suffered water stress at lower reaches of Tarim Rive.

Key words: drought stress, proline, Populus euphratica, the lower reaches of Tarim River