Decrement of nitrate accumulation in Chinese chives through adding NaCl and reducing SO₄^2– concentration in the nutrient solution

Objectives Chinese chives are easy to accumulate NO₃⁻-N, so we tried to reduce the NO₃⁻-N accumulation through adding sodium chloride (NaCl) and reducing the SO₄²⁻ concentration, and studied the mechanism of the nitrogen metabolic pathway.

Methods Trellis growing system was used in a hydroponic experiment of Chinese chive. A specific nutrient solution was used as control (containing SO₄²⁻ 3 mmol/L), and NaCl of 12 mmol/L was added into the solution, SO₄²⁻ concentration of 3, 2, 1 and 0 mmol/L were prepared for treatments of NaCl+S₃, NaCl+S₂, NaCl+S₁ and NaCl+S₀. The Chinese chives were treated for 30 days before sampled for measurement of N, NO₃⁻ and free amino acid contents, and some N-metabolic enzyme activities.

Results Compared with CK, NaCl+S₃ remarkably decreased nitrate content by 32.60%, increased aboveground dry weight, nutrition quality and root activity of Chinese chives (P < 0.05). Reducing SO₄²⁻ concentration to 1 mmol/L (NaCl+S₁) decreased nitrate by 53.30% and increased significantly NaCl+S₃ did in the aboveground dry weight, nutrition quality and root activity. The activities of nitrate reductase (NR) and transaminase (GOT, GPT) were significantly increased, and those of glutamine synthetase (GS) were increased by such an amazing range of 43.57% and 71.43% under NaCl+S₃ and NaCl+S₁ treatments. The NaCl+S₃ and NaCl+S₁ treatments led to the improved serine pathway for free amino acid metabolism and the aspartic pathway for protein synthesis. As a result, the total free amino acid content remained basically unchanged or slightly increased, while the total amino acid hydrolyzed by protein was significantly increased.

Conclusions Adding 12 mmol/L of NaCl and reducing the SO₄²⁻ concentration from 3 mmol/L to 1 mmol/L will stimulate greatly the root activity and the activities of key nitrogen metabolism enzymes, and lead to efficient free amino acid metabolic pathway and the protein synthetic pathway, as a result, increase the dry matter accumulation and nutrition quality of Chinese chives, and reduce nitrate accumulation in Chinese chive.