S08 - Session P8 - Increasing day and night temperature and carbon dioxide concentration influence growth and development of red and green lettuce (Lactuca sativa)

Authors: Devin Brewer *, Sean Tarr, Roberto Lopez

Local, year-round, and consistent leafy green production is possible in indoor controlled environments due to the precise control of radiation intensity, quality, and duration; carbon dioxide (CO 2 ) concentration; vapor pressure deficit; and temperature. Through the manipulation of these parameters, the potential exists to increase crop yield and alter color, flavor, and quality to align with consumer preference. Therefore, our objective was to quantify the influence of day/night temperature and CO 2 concentrations on growth, yield, and quality of lettuce ( Lactuca sativa ). Red oakleaf ' Rouxai ' and green butterhead 'Rex' lettuce seeds were sown in rockwool trays at an average daily temperature (ADT) set point of 22 °C, CO 2 concentration of 500 µmol·mol ‒1 , and radiation intensity of 180 µmol·m ‒2 ·s ‒1 . After 11 days, seedlings were transplanted into deep flow hydroponic tanks among three growth chambers with day/night temperatures and ADTs of 22/15 °C (ADT 20 °C), 25/18 °C (23 °C), or 28/21 °C (26 °C) and CO 2 concentrations of 500, 800, or 1200 µmol·mol ‒1 under l ight -emitting diodes providing 150 µmol·m ‒2 ·s ‒1 for 17-h·d n1 . Temperature and CO 2 independently influenced leaf size and number (LN), growth index (GI), and fresh (FM) and dry mass (DM) for both cultivars. As ADT increased from 20 to 26 °C, FM increased by 35.3 and 32.6 g, GI increased by 22.3 and 12.6%, and LN increased by 6.0 and 8.2 for ' Rouxai ' and 'Rex', respectively. As CO 2 increased from 500 to 800 µmol·mol ‒1 , FM increased by 34.8 and 23.5 g, GI increased by 10.8 and 5.2%, and leaf number increased by 2.2 and 1.7 for ' Rouxai ' and 'Rex', respectively. Our research suggests that increasing both the ADT and CO 2 concentration above 20 °C and 500 µmol·mol ‒1 , respectively, will result in an increased yield; however, increasing the ADT and CO 2 beyond 23 °C and 800 µmol·mol ‒1 , respectively, may be less effective.