Fig. 1. Temperature-gradient greenhouse (TGG) layout illustrating 5- x 2-m field-soil plots of bahiagrass (BG) and rhizoma perennial peanut (PP) in four temperature zones. Each TGG consisted of an entry zone (3.66 m long, not shown), four experimental zones (each 5.49 m long), and one exit zone (1.83 m long, not shown). Arrows indicate the direction of air flow. Heated air was introduced between Zones 1 and 2, 2 and 3, and 3 and 4 to provide step-change in temperature, in conjunction with a variable speed exhaust fan. Both the ventilation fan and the heated air inputs were under computer control. A CO₂ injection system (not illustrated) was provided for two of the four TGGs.