Objective It aims to explore the response of different nitrogen fertilizer levels to the growth and physiological changes of Haloxylon ammodendron seedlings under drought stress, and to provide theoretical basis and technical parameters for ecological restoration and vegetation conservation management in desert areas.

Method The H.ammodendron seedlings in the desert area of Xinjiang were taken as research objects, and the changes of natural drought (water) conditions of the soil were simulated in the critical periods of seedling growth through pot test in high temperature season, and treatments of CK, mild drought, moderate drought and severe drought were set up according to the saturated water holding capacity of the soil, and the nitrogen levels of N0, N1, N2, N3, N4 and N5 (0、0.05、2.50、5.00、7.50、10.00g/m²) were set up respectively under the treatment of each drought gradient. Field collection of each treatment was carried out. The whole plant was labelled, the assimilated branches of labelled seedlings were collected randomly, the biomass of seedlings was determined by indoor drying, and the contents of soluble protein, soluble sugar, proline and malondialdehyde in assimilated branches were analyzed and determined to study the physiological response characteristics of seedlings to drought changes under different nitrogen application levels.

Result Under different drought gradients, taking mild drought as an example, the plant biomass of seedlings showed a trend of increasing and then decreasing with the increase of nitrogen application, and the plant biomass increased from 23.28 g at N0 to 30.19 g at N3 and then decreased to 27.57 g at N5, indicating that excessive application of nitrogen was not conducive to the accumulation of seedling biomass. The contents of soluble protein, soluble sugar, proline and malondialdehyde in the assimilated branches of seedlings increased with the increase of drought gradient at different N application levels. When the assimilated branches were under severe drought, the contents of soluble protein, soluble sugar, proline and malondialdehyde accumulated rapidly, they adapted to the drought through osmoregulation, and the contents of each of them in the assimilated branches at the N3 application level showed the smallest increase compared with that in CK, with the increase of 58.96%, 73.01%, 73.1% and 73.9%, respectively, indicating that reasonable nitrogen application could effectively alleviate drought.

Conclusion Reasonable fertilization is beneficial to the accumulation of seedling plant biomass and effectively alleviate drought stress. It is found that, under the N3 nitrogen application level, the biomass of seedling plant under each drought treatment reached the maximum value, and the contents of soluble protein, soluble sugar, proline and malondialdehyde in the assimilated branches show the least increase with the increase of drought gradient. Considering the comprehensive effect of fertilizer application, it is recommended that 5.00 g/m² of N fertilizer can be added to the conventional planting when artificially planting H. ammodendron transplants in the desert areas of Xinjiang.