Abstract: Investigating the impact of increased nitrogen (N) deposition under drought stress on the ecological stoichiometry of soybean (Glycine max) organs is pivotal for predicting ecological processes and guiding sustainable agricultural development. We explored the effects of simulated nitrogen deposition on N and phosphorus (P) stoichiometry of different organs of soybean cultivar “Tiefeng 29” following drought stress in a pot experiment. There were eight treatments with two water levels: normal moisture (W, 75%±5%), drought (D, 35%±5%), and four N addition levels: CK, LN, MN, HN (nitrogen application was divided into three times, with nitrogen addition amount totaling 0, 50, 100, 150 kg·hm^-2·a^-1). The results showed that the interaction between drought stress and N deposition significantly affected N and P concentration and the N/P ratio in roots, stems, and leaves. Compared with the  CK-D treatment, with the increase of N addition level, root N concentration gradually decreased after one time of N addition, and significantly decreased by 19.3% in the HN-D treatment. The stem P concentration first increased and then decreased, and significantly increased by 38.2% in the LN-D treatment. The leaf P concentration gradually increased, and significantly increased by 31.2% in the HN-D treatment. After two times of N additions, root N concentration was significantly lower than that of CK-D treatment, and there was no significant difference among various N treatments (LN, MN, HN). The stem P concentration gradually decreased, and significantly decreased by 18.9% in the HN-D treatment. The leaf N concentration increased first and then decreased, and significantly increased by 18.5% in the MN-D treatment. After three times of N additions, root N concentration decreased gradually, and significantly decreased by 19.7% in the HN-D treatment. Stem N concentration increased first and then decreased, and significantly decreased by 22.6% in the HN-D treatment. Leaf P concentration was significantly lower than CK-D treatment, and there was no significant difference among treatments (LN, MN, HN). Furthermore, after N application, in the power function relation of leaf N-P (N=βP_α, both α and β are constants), α of W treatment was <1, α of D treatment was >1, with leaf N/P ratios exceeding 16. There was a significant relationship between root and stem N concentration, a highly significant relationship between stem and leaf N concentration, a highly significant positive correlation between root and leaf N concentration, and no significant relationship between stem N and P concentration. In conclusion, early N application can mitigate the negative effects of drought stress on soybean. However, as N deposition increases and the times of nitrogen application rises, soybean growth is limited by P availability.

Key words: drought, nitrogen deposition, plant organ, ecological stoichiometry, soybean