Abstract: Populus euphratica is an important stressresistant germplasm resource for desert riparian forests in Tarim River Basin. The survival and growth of P. euphratica seedlings are always limited by water and nitrogen. In this experiment, we studied the effect of nitrogen supply on the early morphogenesis of P. euphratica seedlings under drought stress. Four water treatments (D₁, D₂, D₃and D₄ with soil relative water contents of 20%-25%, 40%-45%, 60%-65% and 80%-85%, respectively) and three nitrogen application levels (N₀, N₁, N₂: 0, 3, 6 g·pot^-1) were used to determine the growth index, chlorophyll fluorescence and photosynthetic parameters of P. euphratica seedlings. The results showed that under slight drought stress (D₃), P. euphratica seedlings had a higher capacity of growth and photosynthesis when N₁ was applied. Under severe drought stress (D₁), the root/shoot ratio of seedlings was the lowest, and significantly increased when the nitrogen level increased. Under the conditions of drought (D₁, D₂, D₃), the effect of N₁ on seedling growth was higher than that of N₂. Under severe drought stress (D₁), nitrogen application significantly increased the fluorescence parameters and photosynthetic rate. Therefore, P. euphratica seedlings had the best growth performance when soil relative water content was 60%-65% (D₃) and nitrogen application level was 3 g·pot^-1 (N₁). The root growth and photosynthetic capacity of seedlings was significantly increased by nitrogen fertilization under different drought stresses, indicating that nitrogen had a compensatory effect on drought stress. So, nitrogen fertilization can promote the early morphogenesis of P. euphratica seedlings and help the seedlings survive during the vulnerable period of growth.

Key words: environmental safety assessment., rhizobia, Illumina Miseq pyrosequencing, glyphosate-resistant transgenic soybean, bacteria