Abstract: The potted control experiment method was used to analyze Populus euphratica Oliv. strategies to tolerate low nitrogen. The results showed that: Populus euphratica Oliv. plants have high carbon-nitrogen ratio to maintain a high nitrogen utilization rate; under low nitrogen stress, Populus euphratica Oliv. nitrates preferentially meet the shoots; roots and shoots have opposite nitrate assimilation rate-limiting enzymes (nitrate reductase). The activity change promoted the NO-3 transportation of the shoots and the transcription level of the NRT1.5C/NRT1.8B protein, which was responsible for the long-distance nitrate transportation of the xylem, further accelerated the NO-3 transportation of the shoots. At the same time, it was responsible for the transportation of nitrate from old leaves to young leaves. The increasing transcription level of the protein PeNRT1.7 accelerated the plant nitrogen nutrient turnover. Result showed that the root monovalent anions NO-3 and Cl- content greatly decreased under low nitrogen, and the K+ content of NO-3 long-distance transportation was reduced, resulting in a compensatory increase in the divalent ions SO2-4, Ca2+, and Mg2+, thereby ensured the plant ion balance. Therefore, Populus euphratica Oliv. could effectively adapt to moderate nitrogen stress through reasonable ion allocation and carbon and nitrogen balance strategies.

Key words: low nitrogen stress, ionic homeostasis, long-distance transportation of nitrate, carbon and nitrogen balance