EFFECTS OF VARYING NO3-:NH4+ RATIOS ON LETTUCE (LACTUCA SATIVA L.) NITROGEN METABOLISM

The two main forms of nitrogen (N) in plants are Nitrate (NO3-) and ammonium (NH4+). The effects of different nutrient solution NO3-:NH4+ ratios (0:100, 25:75, 50:50, 75:25, and 100:0) on the biomass, photosynthetic parameters, activity of key N metabolism enzymes, mineral contents and quality of hydroponically grown lettuce were evaluated. The results showed that total dry biomass, the total fresh biomass and root length were the maximum at the 75:25 NO3-:NH4+ ratio and that the water content was the highest by a significant margin at 25:75. The leaf intercellular CO2 concentration (Ci) , net photosynthesis rate (Pn), and stomatal conductance (Gs) of lettuce were the highest at 75:25, and the transpiration rate (Tr) was the maximum at 50:50. The Ca and Fe contents in lettuce were the highest at 100:0, and the N and Mg contents were the highest at 75:25. The activities of key enzymes related to N metabolism, nitrite reductase (NiR), nitrate reductase (NR), glutamine synthetase (GS), asparagine synthetase (AS), glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH), were the greatest at 75:25, and the nutritional quality of lettuce in terms of the soluble sugar, vitamin C (Vc) and soluble protein contents was the highest at 75:25. The results showed that when the ratio of NO3-:NH4+ was 75:25, the most conducive to lettuce growth.

Automated summary

The NO3-:NH4+ ratio significantly affects the growth and quality of hydroponically grown lettuce. Overall, a ratio of 75:25 has been found to be the most conducive for lettuce growth and nutritional quality. Other ratios also have varying effects on different physiological parameters and mineral contents of lettuce.