EFFECTS OF CARBON DIOXIDE AND NITROGEN COUPLING ON GROWTH, ANTHOCYANIN AND NUTRIENTS ABSORPTION OF HYDROPONIC PURPLE LETTUCE

Nutrient substances and supplementary carbon dioxide (CO2) are essential for water planting, increasing hydroponic vegetables growth. In this paper, a treatment of 200g CO2 growth agent once a week (C1) was supplied when purple lettuce was planted in hydroponic solutions with different nitrogen concentration, at 100% (N100), 80% (N80) and 60% (N60) of 381.24 g/L nitrogen in solution, respectively. Each nitrogen solution was also done with no applying CO2 (CO). Therefore, six treatments as C1N100, C1N80, C1N60, C0N100, C0N80 and C0N60 were set. Plant height (H), number of leaf (NL), maximum leaf area (LA), yield (Y), SPAD value, contents of nitrogen (N), phosphorus (P) and potassium (K) in plant were investigated to analyze coupling effects of carbon dioxide and nitrogen. Results showed that the applying CO2 interacted with nitrogen in solution could obviously improve hydroponic lettuce growth, SPAD and plant nutrients, but took disadvantage of anthocyanin (OPC). The added air CO2 could enhance N and P absorption in lettuce. The C1N60 treatment received the significantly largest Y at 42.93 g/plant, H at 22.20 cm, LA at 354.57 cm(2), and plant N at 4.99% (P<0.05), enhancing SPAD, plant P and K to some extent. Noticeably, all treatments under added air CO2 received a significantly lower values of OPC (P<0.05), with C0N60 obtaining the greatly biggest OPC content followed with C0N80 and C0N60. To sum up, a suitable increased air CO2 and lower nitrogen in hydroponic solution would increase lettuce growth and plant nutrient element, but its effect on anthocyanin should be thought a twice.