Abstract: 【Objective】Research has been carried out to study the effect of ammonium-enhancement nutrition on organic acid and starch content in spinach (Spinacia oleracea L.). 【Method】Hydroponic experiments were conducted in greenhouse，nitrogen form changed by properly increasing ammonium concentration in nutrient solution. Measurements included organic acids, starch, nitrate and soluble oxalate contents. 【Result】Content of pyravate, citrate, α-ketoglutarate, succinate, fumarate and malate in spinach shoots increased with the decrease in NH4+-N/ NO3--N ratio, and which were significantly and positively correlated with nitrate content in nutrient solution. (2) Content of pyravate, citrate, succinate and malate in spinach roots also increased with the decrease in NH4+-N/ NO3--N ratio, which didn′t significantly affected fumarate content. (3) With the decline of NH4+-N/NO3--N ratios, ratios of pyravate, α-ketoglutarate, succinate, fumarate and malate content of roots to that of shoots in spinach tended to decrease, while the ratio of citrate content gradually increased. (4) Starch content in both of shoot and root in spinach tended to decrease with the decrease in NH4+-N/NO3--N ratio, and starch content in both of shoots and roots were negatively correlated with the nitrate content in nutrient solution. 【Conclusion】With the increase of proportion of nitrate in nutrient solution, metabolism of organic acids enhanced to provide enough energy and carbon skeleton for protein synthesis. It is obviously that, proper partial replacement of NO3--N by NH4+-N was beneficial to decreasing content of nitrate, nitrite and oxalate in spinach, while soluble sugar content increased. Therefore, increasing ammonium in the nutrient solution could improve the nutritional quality of spinach.

Key words: Spinach, Ratio of Ammonium to nitrate, Organic acid, Starch