Uptake and nitrate accumulation affected by partial replacement of nitrate-N with different source of amino acids in spinach and lettuce

As natural plant growth stimulators, amino acids are widely used to improve the yield and quality of crops. Change in enzymes activities of N assimilation (NR, NiR and GS), residual nitrate (NO3-), soluble protein content, and yield of spinach and lettuce plants were investigated under replacing 20% nitrate-N in the nutrient solution by L-glycine and blood meal amino acids. Seeds of the mentioned plants were sown in soilless medium for two weeks in the growth chamber. Seedlings in double leaf stage were transferred into the pots. After 30 days from transplanting, 20% of nitrate in the nutrient solution was replaced by L-glycine and a mixture of amino acids extracted from blood meal. Compared with the full nitrate treatment, amino acids replacement caused decrease in nitrate accumulation in the leaves of studied plants. The decrease in nitrate accumulation was accompanied by a decrease in nitrate reductase activity, an increase in glutamine synthetase and high production of amino acids and chlorophyll content. The amino acids present in the blood meal were more effective than the L-glycine treatment to reduce the nitrate concentration in spinach (1.72%) and lettuce (17.5%). Compared to the full nitrate treatment, partial replacement of blood meal amino acids increased the soluble protein content in the leaves of spinach (67.36%) and lettuce (83.82%). Supplying with amino acids significantly enhanced total nitrogen and dry matter in the studied plants, although effects of blood meal amino acids treatment were higher than L-glycine. Based on the results, partial replacement of nitrate with amino acids could cause decrease in nitrogen accumulation in spinach and lettuce plants.