Real-time Monitoring of Photosynthesis and Transpiration of a Fully-grown Tomato Plant in Greenhouse

A real-time photosynthesis and transpiration monitoring system was developed and applied to monitor the time course of photosynthesis and transpiration of fully-grown tomato plant in a semi-commercial greenhouse. The system is composed of an open-bottom chamber and a sensing unit. The chamber encloses a two-meter high tomato plant with transparent film. The two fans equipped at the top of the chamber exhaust interior air and the open bottom allows exterior air to move into the chamber. The inflow- and outflow-air were continuously sampled, and their CO2 and H2O concentrations were measured. The developed system successfully traced the time courses of net photosynthetic and transpiration rates on typical sunny and rainy days. A decrease in net photosynthetic rate, which might be due to the stomatal closure caused by drought stress, was observed on the sunny day. On the other hand, negative net photosynthetic rate and transient increase in net photosynthetic rate and transpiration rate caused by the supplemental lighting were observed on the rainy day. In addition, the dark respiration rate was recognized during nighttime. These results suggest that the developed system can be a useful tool to evaluate the dynamic changes in photosynthesis and transpiration of crops in greenhouse.