A system for measuring the in situ CO₂ exchange rates of in vitro plantlets

A system was designed for measuring the CO₂ exchange rates [net photosynthetic rate (P(n)) and dark respiration rate] of in vitro plantlets in situ (in the vessel with natural ventilation). The system, excluding gas cylinders, was placed in a growth chamber so that the desired photosynthetic photon flux (PPF) and temperature could be maintained during the measurement. The CO₂ concentration inside the culture vessel (C(i)) was indirectly controlled by controlling the CO₂ concentration outside the vessel (C(o)). The P(n) of the plantlets was estimated based on the measured C(i) and C(o) at steady state using a gas chromatograph according to the method described by Fujiwara et al. (1987). The performance of the system was demonstrated by measuring the in situ P(n) of sweetpotato [Ipomoea batatas (L.) Lam., cv. Beniazuma] and tomato (Lycopersicon esculentum Mill., cv. Hana Queen) plantlets in vitro under a range of CO₂ concentrations and PPF. The photosynthetic parameters of the P(n) model (Niu and Kozai, 1997) for the plantlets were then estimated based on the measured P(n). The preliminary measurements demonstrated the potential application of the system.