Abstract:

The combined effects of sodium chloride（NaCl）and nitrogen fertilizer on the fruit quality formation of Ziziphus jujuba‘Zhanhua Dongzao 1’were studied，which will provide a theoretical basis for nitrogen management and the improvement of fruit quality under saline alkali environment. In the greenhouse，the solutions of different NaCl concentrations（0，1，3 and 5 g · L^-1）and nitrogen concentrations（0，2，4 and 8 g · L^-1）were used as irrigation water for potted seedlings of‘Dongzao’jujube. The results showed the leaf nitrogen content，chlorophyll content and net photosynthetic rate（P_n）that treated with 3 g · L^-1 NaCl and 4 g · L^-1 nitrogen fertilizer kept a higher level among all treatments. While 5 g · L^-1 NaCl treatment significantly inhibited nitrogen absorption，resulting in the lowest photosynthetic capacity when it interacted with 8 g · L^-1 nitrogen treatment. Under the same NaCl concentration，4 g · L^-1 nitrogen fertilizer had the best effect on reducing the accumulation of Na⁺ and increasing the content of K⁺ in fruits. When 5 g · L^-1NaCl was added but no nitrogen fertilizer was applied，the K⁺/Na⁺ value of fruit decreased to the lowest among all treatments. With the increase of NaCl concentration，the fruit fructose，glucose and sucrose content increased to the highest value under 3 g · L^-1 NaCl treatment，and then decreased to the lowest value under 5 g · L^-1 NaCl treatment. Under the same NaCl concentration，the addition of 4 g · L^-1 nitrogen fertilizer could significantly increase the content of three sugar components. 5 g · L^-1 NaCl treatment could promote the accumulation of malic acid，while 8 g · L^-1 nitrogen treatment could promote the accumulation of citric acid. Under the treatment of 5 g · L^-1 NaCl，no nitrogen or 8 g · L^-1 nitrogen fertilizer would make the total acid content of fruit very high. To sum up，the combination of 3 g · L^-1 NaCl and 4 g · L^-1 nitrogen fertilizer could improve the photosynthetic capacity of leaves，maintain the balance of mineral elements in cells，promote the accumulation of main sugar components in fruits，and increase the sugar acid ratio，which is most beneficial to the improvement of fruit quality. While，under 5 g · L^-1 NaCl stress，too little（no nitrogen）or too much（8 g · L^-1 nitrogen）nitrogen fertilizer resulted in ion toxicity，damaged the function of leaves，thus caused nutrient deficiency and excessive accumulation of organic acids in the fruits，which is not conducive to quality formation.

Key words: Ziziphus jujuba, salt stress, nitrogen level, interaction, quality formation