Effects of Nitrogen on Root Development and Contents of Bioactive Compounds in Salvia miltiorrhiza Bunge

Production protocols for the cultivation of high-yielding and high-quality Salvia miltiorrhiza Bunge are needed because of the expanding markets for high-value Danshen. A 2-yr pot experiment was conducted to investigate the effect of nitrogen (N) levels and ratios of ammonium nitrogen (NH4+-N) to nitrate nitrogen (NO3--N) on root development and contents of bioactive components of S. miltiorrhiza Bunge in a soil culture system. The S. miltiorrhiza Bunge seedlings were provided with three N levels (0, 3, and 6 g N plant(-1)) at the same NH4+:NO3- ratio (0:100) and five NH4+:NO3- ratios (0:100, 25:75, 50:50, 75:25 and 100:0) at the same N level (3 g N plant(-1)). The plant dry matter (DM), the apparent property of roots, and the contents of cryptotanshinone, tanshinone IIA, total tanshinones, danshensu, and salvianolic B in roots were examined. Plant growth and all the contents of the bioactive components responded negatively to increasing N availability, suggesting that S. miltiorrhiza Bunge is not a nitrophile. The best apparent property of roots and the highest DM were consistently observed when the NH4+:NO3- ratio was 75:25. However, the NH4+:NO3- ratios required for the highest content and yield of bioactive compounds varied among the different compounds. Therefore, in the commercial cultivation of S. miltiorrhiza Bunge, the NH4+:NO3- ratio should be chosen according to the target compound, considering the DM and apparent property of roots and the contents of the desired compounds. Further studies are needed to elucidate the mechanisms in terms of photosynthesis, the activities of key enzymes, and the biosynthetic pathway of the bioactive compounds.