Empirical Model for the Estimation of Whole-plant Photosynthetic Rate of Cherry Tomato Grown in a Commercial Greenhouse

There have been many works to improve productivity of greenhouse-grown tomato. One effort is to analyze the photosynthetic rate as it influences productivity (Hisaeda et al., 2007; Takayama et al., 2010). Thus, quantifying photosynthetic rates is essential to diagnose the plant condition as well as to achieve the optimum cultivation condition in the greenhouse in the speaking plant approach concept (Hashimoto, 1989; Udink ten Cate et al., 1978). To bridge the plant’s photosynthesis and greenhouse climate control, many researchers developed various kinds of mathematical models of the environmental response of photosynthesis. The models were used as research tools or analytical means, for forecasting, or to be implemented in a computerized system for climate control (Nederhoff and Vegter, 1994). Thornley’s model (Thornley, 1976), Acock’s model (Acock et al., 1978), TOMGRO (Dayan et al., 1993), and TOMSIM (Heuvelink, 1996) are some established models. Some studies used photosynthesis measurements of single-leaf (Thornley, 1976; Acock et al., 1978; Xin et al., 2019), other studies used canopy-level measurements in a closed chamber (Acock et al., 1978), or whole-greenhouse (Nederhoff and Vegter, 1994; Tsafaras and de Koning, 2017). However, these studies could not provide a realtime response of the photosynthesis of a full-size plant, as part of a community under greenhouse condition, to its environment. Furthermore, the variables used in the photosynthesis models vary among the models. The Thornley’s model used incident light flux density, ambient CO2 concentration, and dark respiration rate with three other parameters to calculate net photosynthesis of single leaf (Acock et al., 1978). The model was then constructed by Acock et al. (1978) for canopy photosynthesis in tomato. Nederhoff and Vegter (1994) used variables of photosynthetically active radiation (PAR, i.e., light flux, 400―700 nm), CO2 concentration, and leaf area index (LAI) in an empirical photosynthesis model. However, other environmental factors may also contribute to photosynthesis activity. Based on previous literature, photosynthesis activity has an apparent response to temperature (Castilla, 2013), and is affected by vapor pressure deficit (Acock et al., 1976; Shamshiri et al., 2018). The objective of the present study was to develop an empirical model for the estimation of the whole-plant net photosynthetic rate (Pn) of cherry tomato as a function of relevant greenhouse environmental factors. We used data of Pn at the whole-plant level as a real-time response to instantaneous PAR, air temperature, vapor pressure deficit,