DIURNAL MACRONUTRIENTS UPTAKE PATTERNS BY LETTUCE ROOTS UNDER VARIOUS LIGHT AND TEMPERATURE LEVELS

In order to reduce nutrient wastes to the environment the supply should be in accordance to the demand for these. Two experiments were conducted to study and quantify the effect of temperature, irradiance, and plant age on the uptake of nitrate (NO3-), ammonium (NH4+), dihydrogen phosphate ion (H2PO4-), potassium (K+), calcium (Ca2+), magnesium (Mg2+), and sulfate (SO42). In the first experiment, various levels of temperature and irradiance were applied to plants in a growth chamber, while in the second experiment the uptake was studied along the crop season under greenhouse conditions. The uptake rates were calculated at 2-hour intervals through sampling the nutrient solution and analyzing it by inductively coupled plasma atomic emission spectrometry (ICP-AES). Increasing light and temperature enhance the uptake rates, while the rates decrease with plant age. Nitrogen absorption was similar during the day as during the night. No differences were found in the absorption of H2PO4-, K+, Ca2+, Mg2+, and SO42- between day and night. Nitrate absorption was found to have a positive correlation with the absorption of all the ions except for NH4+.