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. 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, 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.