Diurnal Macronutrients Uptake Patterns by Lettuce Roots under Various Light and Temperature Levels

Abstract

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⁺.

Keywords:

• lettuce macronutrient absorption
• diurnal uptake variation
• nutrient interactions

FUNDING

The authors would like to thank the kind support of General Hydroponics, Inc. and Fulbright-CONICYT Chile in this study.