2.3. Greenhouse environment
The experiment was conducted in a glass-glazed greenhouse at Michigan State University (East Lansing, MI) maintained at a constant air temperature set point of 20 °C as controlled by a greenhouse environmental control system (Integro 725; Priva North America, Vineland, ON, Canada). Roof and side vents, cellulose evaporative-cooling pads, and exhaust fans in the greenhouse were used for ventilation and cooling when needed. In addition, whitewash was applied externally on the greenhouse glass during the second replication to reduce solar heating in the greenhouse. An aspirated thermocouple [36-gauge (0.127-mm diameter) type E] located in the middle of each bench measured air temperature at plant height every 10 s, and a data logger (CR10; Campbell Scientific, Logan, UT) recorded hourly means. The data logger controlled a 1500-W electric heater underneath each bench to automatically switch on to provide supplemental heat when the nighttime air temperature at plant height was