Effects of High CO2 on Respiration in Various Horticultural Crops

Under 60% CO2+20% O2+20% N2, the respiration rates of various fruits and vegetables, based on O2 uptake, were measured using an automated system aided by a micro-computer. With high CO2 treatment, O2 uptake rates of apples and melons declined to approximately one-half of the initial level. Ripening tomatoes and bananas also showed a respiratory reduction by high CO2 but these fruits, at pre-climacteric stage, showed little change in respiration. Exposure to high CO2 caused slight or no change in respiration with Natsudaidai (C. natsudaidai Hayata), lemons, potatoes, sweet potatoes and cabbage. Like the ripening climacteric fruits tested in this study, the respiration rate of broccoli was reduced by high CO2 exposure. In contrast, a stimulation in respiration by high CO2 was observed in lettuce, eggplants and cucumbers.These results demonstrate that respiratory responses to high CO2 were quite different with the kind of horticultural crops and their developmental stage, and raise a doubt as to the inhibitory effects of high CO2 on respiration, which has been accepted by most researchers.