Relationship between positions of CO₂ supply in a canopy of tomato grown by high-wire system and distribution of CO₂ concentration in a greenhouse

Abstract

　This study aimed to propose an effective positions of CO₂ supply in tomato plants grown by high-wire system to reduce CO₂ leakage from a naturally ventilated greenhouse. CO₂ was supplied at two different positions within the tomato canopy, and CO₂ concentration was measured at different heights above the ground within or outside the canopy under ventilated or unventilated conditions in the greenhouse. CO₂ supply started below 400 µmol mol^-1 of the CO₂ concentration measured at 2.4 m above the ground and stopped at 450 µmol mol^-1. When CO₂ was supplied at the base of the canopy (0.6 m above the ground), the CO₂ concentration near the top of the canopy (2.4 m above the ground) was below 400 µmol mol^-1 in some cases. On the other hand, when CO₂ was supplied at the middle layer of the canopy (1.2 m above the ground), the CO₂ concentration within the canopy (1.2 to 2.4 m above the ground) was maintained around 450 µmol mol^-1 regardless of ventilated or unventilated conditions. The CO₂ concentration below the roof windows (4.2 m above the ground) was hardly increased by changing the position of CO₂ supply from 0.6 to 1.2 m above the ground. The CO₂ concentration at 4.2 m above the ground under unventilated condition was slightly above 400 µmol mol^-1, which was almost the same as that under ventilated condition. In summary, it was suggested that the CO₂ supply at the middle layer of the canopy was more appropriate than at the base of the canopy to elevate the CO₂ concentration within a canopy of tomato grown by high-wire system. In addition, the CO₂ supply at the middle layer of the canopy was seemed to have a low CO₂ leakage from the top windows even in the ventilated greenhouse.