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

Abstract

Maximization of crop net photosynthesis is one of the most important objectives of environmental control in greenhouses (Takayama, 2013). To increase the crop photosynthesis, instrumentations such CO2 enrichment, supplemental lighting and so on have been installed in commercial greenhouses (Vanthoor et al., 2011). To establish the appropriate environmental control in greenhouse, plant diagnosis techniques are important and the Speaking Plant Approach (SPA) is regarded as a sophisticated concept (Udink ten Cate et al., 1978; Hashimoto, 1980). In the plant diagnosis techniques, measurement of photosynthetic rate is important to monitor the plant physiological status and performance of assimilation. Nevertheless, many open gas-exchange systems have been designed to measure leaf photosynthetic rate (Dutton et al., 1988) and there is no appropriate instrumentation to monitor fully-grown/fullsize crop photosynthetic rate in commercial greenhouse. Many studies estimated the crop photosynthesis by using the previously measured photosynthesis light response curve at single leaf level, incoming radiation, canopy light profile and the leaf area index (Spitters et al., 1989; Jones, 1992; Cannell and Thornley, 1998; Li et al., 2014). However, the environmental response of photosynthesis at single leaf level does not represent the crop photosynthesis (Dutton et al., 1988). Especially, Paradiso et al. (2011) reported that the spectral dependence of light absorption and photosynthesis at the canopy level is different from that at leaf level. Furthermore, canopy architecture of tomato plant has a large impact on crop light distribution and photosynthesis (Sarlikioti et al., 2011). On the other hand, Zekki et al. (1999) and Teitel et al. (2011) proposed a monitoring of CO2 balance at a greenhouse level to measure the net photosynthetic rate of all the plants grown in the greenhouse. However, it is difficult to evaluate the fluctuated ventilation rate of the greenhouse at high time resolution, so these techniques provide low time resolution data. Therefore, a real-time monitoring of photosynthesis of a full-size plant grown in greenhouse has been required for SPA. There are several whole plant level open chambers for trees or herbaceous plants (Munakata, 1970; Miller et al., 1996; Ferrai et al., 2016), however they are