Influence of day and night temperature and carbon dioxide concentration on growth, yield, and quality of green butterhead and red oakleaf lettuce

Production of lettuce (Lactuca sativa) within vertical farms is an expanding segment of controlled environment agriculture-precise manipulation of environmental parameters including mean daily temperature (MDT) and carbon dioxide (CO2) concentration enables year-round production, alongside color, yield, and crop size regulation. Our objectives included 1) quantify how MDT and CO2 interact to influence lettuce growth, development, and quality; 2) model lettuce growth under several MDTs and CO2 concentrations. Green butterhead 'Rex' and red oakleaf 'Rouxai RZ' seedlings were transplanted into hydroponic tanks under a photosynthetic photon flux density of 300 mu mol.m(-2).s(-1) for 17-h.d(-1). CO2 concentrations of 500, 800, or 1200 mu mol.mol(-1) and day/night and MDT setpoints of 22/15 degrees C (MDT 20 degrees C), 25/18 degrees C (23 degrees C), or 28/21 degrees C (26 degrees C) were maintained within growth chambers. 'Rex' fresh mass increased linearly with MDT, increasing by 18% from 20 to 26 degrees C. 'Rouxai RZ' fresh mass increased quadratically with MDT, with a 32% increase from 20 to 23 degrees C, then a 7% increase from 23 to 26 degrees C. Elevating CO2 concentrations from 500 to 800 mu mol.mol(-1) increased 'Rouxai RZ' and 'Rex' fresh mass by 33 and 16%, respectively, while fresh mass did not increase from 800 to 1200 mu mol.mol(-1). Both cultivars had the greatest dry mass at 800 mu mol.mol(-1) CO2 across temperatures. At a high MDT, 'Rouxai RZ' foliage color became more light, vibrant, and green, while a low MDT induced darker, grayer, and redder foliage. Tipburn occurred on 'Rex' across treatments, while 25% of 'Rouxai RZ' were afflicted at 500 mu mol.mol(-1) CO2 and 67% at 1200 mu mol.mol(-1). At the light intensity studied, we recommend growing 'Rex' and 'Rouxai RZ' at an 800 mu mol.mol(-1) CO2 concentration and MDT of 23 degrees C for greatest biomass and leaf number, and slightly redder foliage in 'Rouxai RZ' than at a 26 degrees C MDT.