N, P, K and S uptake response to various levels of CO2 assimilation and growth rate in lettuce

Abstract

ABSTRACTUnder conditions of limited nutrient supply, plant nutrient uptake is controlled by the external concentration of the ions. Limited information exists about the whole-plant regulation of nutrient uptake when the supply is adequate. To study the relationship between growth rate and carbon dioxide (CO2) assimilation with nutrient uptake, growth chamber experiments were conducted with temperatures ranging from 10 to 35°C at medium (600 µmol m−2 s−1) and high (1200 µmol m−2 s−1) light intensities. Nutrient solution samples were collected every 24 hours and the concentration of ions was analyzed by Inductively coupled plasma -atomic emission spectroscopy (ICP-AES) and nitrate and ammonium (NO3−/NH4+) conductivity. Leaf photo-synthesis was measured using a closed gas exchange system and the total amount of CO2 assimilated was calculated from dry weight increases. The daily absorption of NO3−, Total nitrogen (N), dihydrogen phosphate (H2PO4−) and potassium (K+) responded linearly to plant growth, while ammonium (NH4+) and sulfate (SO42−) uptake showed a curvilinear response. All the ions studied showed a curvilinear relation with CO2 assimilation.