Abstract:

A hydroponic planting experiment in the southern plastic greenhouse with lettuce was conducted to investigate the effects of two nutrient solution concentrations supply on leaf number, plant height, fresh weight, dry weight and leaf nutrient element content (Ca, Mg, Fe, Mn, Cu, Zn) at different growth stages under high temperature environment. The two levels of temperature environment for lettuce growth were set as high temperature environment (H) and normal temperature environment (N). The nutrient solution concentration was expressed by EC (μS·cm⁻¹), which was set as normal concentration (CK, 1500μS·cm⁻¹) and elevated concentration (C1, 1900μS·cm⁻¹). The results showed that, (1) high temperature environment increased daily average temperature in the growth of lettuce leaves and nutrient solution by 13.9℃ and 12.0℃, daily minimum temperature by 13.9℃and 11.8℃, daily maximum temperature by 14.4℃and 12.7℃, respectively, compared with normal temperature environment. (2) Under normal temperature environment, elevated concentration increased leaf number, plant height, shoot fresh weight, root fresh weight, shoot dry weight and root dry weight at the harvesting stage by 15.2%, 16.9%, 63.2%, 24.4%, 28.5% and 6.6%, respectively, compared with normal concentration. However, under high temperature environment, normal concentration increased above growth indicators by 54.2%, 41.0%, 249.5%, 496.0%, 169.6% and 353.4% at the harvesting stage, respectively, compared with elevated concentration. (3) High temperature environment promoted the contents of Ca, Mg and Fe in lettuce leaves. Under normal temperature environment, elevated concentration significantly promoted the contents of Mn and Cu in lettuce leaves at the harvesting stage by 22.7% and 61.5%, while unsignificant difference occurred in the contents of Ca, Mg, Fe and Zn, compared with normal concentration. Furthermore, under high temperature environment, normal concentration significantly promoted the contents of Ca and Mn in lettuce leaves at the harvesting stage by 34.5% and 44.9%, while didn’t affect the contents of Mg, Cu and Zn significantly, compared with elevated concentration. It is suggested that temperature environment and nutrient solution concentration have significant effects on hydroponic lettuce growth and nutrient absorption, and increasing lettuce yield, quality and fertilizer efficiency can be achieved by adjusting nutrient solution concentration during the actual production of hydroponic lettuce in Summer and Autumn/Winter.

Key words: High temperature environment, Nutrient solution concentration, Hydroponic lettuce, Nutrient elements, Plastic greenhouse