Abstract: We investigated the effects of exogenous signal hydrogen sulfide (H₂S) on nitrogen metabolism and yield components of naked oats (Avena nuda) under saline-alkali stress. The naked oat cultivar ‘Dingyou 9’ was used as materials with potted soil culture. Plants at the heading stage were sprayed with 50 μmol·L^-1 H₂S donor sodium hydrosulfide (NaHS) solution for three days to explore its effects on the substance contents and activities of key nitrogen metabolism-related enzymes in leaves under 3.00 g·kg^-1 saline-alkali (the molar ratio of NaCl∶Na₂SO₄∶Na₂CO₃∶NaHCO₃=12∶8∶1∶9) stress. The water spraying was used as the control (CK). The yield and its components were counted after maturity. The results showed that, on the 7th day after spraying for three days, compared with the CK, the saline-alkali stress significantly reduced the contents of ammonia nitrogen, nitrate nitrogen and soluble protein, as well as the activities of protease, glutamine synthetase (GS), glutamate synthase (GOGAT), glutamate dehydrogenase (GDH), glutamic-oxaloacetic transaminase (GOT), and glutamic-pyruvic transaminase (GPT) in naked oat leaves, but did not affect free amino acid content and nitrate reductase (NR) activity. Spraying NaHS solution significantly decreased the contents of ammonia nitrogen and free amino acids and the activities of protease and GPT in leaves under saline-alkali stress by 27.3%, 51.4%, 51.4% and 8.3%, respectively, and the activities of GDH and GOT were significantly increased by 12.1% and 36.1%, respectively. The contents of nitrate and soluble protein and the activities of NR, GS and GOGAT were not altered. On the 14th day after spraying for three days, saline-alkali stress led to a significant decrease in the contents of ammonia nitrogen and soluble protein and the activities of protease, GS and GOGAT in leaves, and a significant increase in the content of nitrate and the activities of NR, GDH and GOT, while the content of free amino acids and the activities of GPT did not change. Spraying NaHS solution significantly decreased the activities of GDH and GOT in leaves under saline-alkali stress by 62.3% and 53.2%, respectively, and the contents of soluble protein and free amino acids and the activities of protease, GS, GOGAT and GPT in leaves increased significantly by 19.5%, 39.0%, 71.5%, 294.6%, 149.7% and 23.7%, respectively. The content of ammonia nitrogen and the activity of NR did not change significantly. Saline-alkali stress did not affect aboveground dry weight, harvested ears, spike boll number, and thousand-grain weight of naked oats, but significantly decreased the spike grain numbers and grain yield by 44.5% and 43.6%, respectively. Spraying NaHS solution did not affect aboveground dry weight, harvested ears, spike boll number, and thousand-grain weight of naked oats under saline-alkali stress, but significantly increased the spike grain numbers and grain yield by 61.6% and 52.8%, respectively. Those results indicated that saline-alkali stress disturbed nitrogen metabolism of naked oats, resulting in a decrease in yield. Exogenous hydrogen sulfide could alleviate the decline in yield components and yield of naked oats under saline-alkali stress by regulating nitrogen metabolism.

Key words: saline-alkali stress, hydrogen sulfide, naked oat, nitrogen metabolism, yield component.