An orthogonal test of the effect of NO3-, PO43-, K+, and Ca2+ on the growth and ion absorption of Elaeagnus angustifolia L. seedlings under salt stress

Excess salts in soil severely inhibit plant growth and yield. Various nutrients can relieve the inhibitory effect of salt on plants. Elaeagnus angustifolia is a tree species that is utilized in landscaping and ecological restoration in China and shows tolerance to saline soils. In this experiment, we first determined the optimal concentration of single-nutrient inputs for promoting growth of E. angustifolia seedlings and alleviating salt stress. The optimal nitrogen (NO3-), phosphorus (PO43-), potassium (K+), and calcium (Ca2+) concentrations under salt stress were 2, 0.6, 2, and 2 mM, respectively. Based on this result, we carried out an optimum nutrient ratio experiment by a four-factor and three-level orthogonal experiment. The results showed that under normal growth conditions, the optimal nutrient combinations for NO3-, PO43-, K+, and Ca2+ were 2, 0.6, 5, and 1 mM; 5, 0.2, 5, and 2 mM; and 5, 0.6, 1, and 5 mM, respectively, which increased plant height, biomass, and the chlorophyll content of E. angustifolia seedlings. Under salt stress, the optimal nutrient combinations were 5, 0.2, 5, and 2 mM; and 5, 0.6, 1, and 5 mM, respectively. This study provides a theoretical basis for optimal fertilization of E. angustifolia seedlings in saline-alkali soils.