Effects of the nitrate and ammonium ratio on plant characteristics and Erythropalum scandens Bl. substrates

Erythropalum scandens Bl. is a woody vegetable with high nitrogen demand that inhabits southern China. Ammonium and nitrate are the two main forms of inorganic nitrogen that plants directly absorb. A pot experiment was performed to determine the growth, physiological responses, and preferences of 12-month-old E. scandens seedlings for ammonium and nitrate. Aboveground and underground growth indexes, biomass, physiological and biochemical indexes (chlorophyll [Chl], soluble sugar, soluble protein and free proline contents), and substrate pH and nitrogen contents were determined under different nitrate and ammonium ratios (0 NO(3)(-): 100 NH(4)(+), 25 NO(3)(-): 75 NH(4)(+), 50 NO(3)(-): 50 NH(4)(+), 75 NO(3)(-): 25 NH(4)(+), and 100 NO(3)(-): 0 NH(4)(+)), and the control (0 NO(3)(-): 0 NH(4)(+)). The results showed that ammonium and nitrate improved the growth and physiological status of E. scandens seedlings in most of the treatments compared to the control. The aboveground growth status and biomass accumulation of E. scandens seedlings were significantly better under the 0 NO(3)(-): 100 NH(4)(+) treatment during fertilization compared with all other treatments. However, the growth status of the underground parts was not significantly different among treatments. Significant differences in osmoregulator content, except for soluble sugars, and Chl content were observed. Soluble sugars and soluble proteins were highest under the 0 NO(3)(-): 100 NH(4)(+) treatment at the end of fertilization (day 175). However, free proline accumulated during fertilization and the increase in NO(3)(-) indicated that excessive use of NO(3)(-) had a negative effect on the E. scandens seedlings. The order of accumulating nitrogen content was leaves > roots > stems. The highest N accumulation occurred in the aboveground parts under the 0 NO(3)(-): 100 NH(4)(+) treatment, whereas the highest N accumulation occurred in the underground parts under the 50 NO(3)(-): 50 NH(4)(+) treatment. Substrate pH increased at the end of fertilization (day 175) compared with the middle stage (day 75), while total nitrogen, ammonium, and nitrate were highly significantly different among the treatments. Total nitrogen and NH(4)(+) content were the highest under the 0 NO(3)(-): 100 NH(4)(+) treatment, while NO(3)(-) content was the highest under the 100 NO(3)(-): 0 NH(4)(+) treatment. In conclusion, 12-month-old E. scandens seedlings grew best, and had better physiological conditions in NH(4)(+) than NO(3)(-). The 0 NO(3)(-):100 NH(4)(+) treatment (ammonium chloride 3.82 g/plant) resulted in the best growth and physiological conditions. Most of the growth and physiological indexes were inhibited with the increase in nitrate.