In search of the optimal greenhouse tomato row orientation using functional-structural plant modeling, with focus on stomatal conductance.
MSc-thesis abstract (submitted 27 June 2016): Greenhouse tomato growers can control the climatic factors to a certain extent with different approaches. A group of them are the structural traits of the growth system, of which row orientation influences light interception by the plants, and light dynamics, thus photosynthesis and transpiration. Therefore, finding an optimal row orientation of greenhouse tomato may lead to better yield and increase the profitability of the production.
Stomatal conductance is an important factor, since it controls both the CO2 supply for assimilation and the water loss through transpiration, furthermore, it is a mid term reducing element of photosynthesis during light fluctuations. Therefore, modeling stomatal conductance is not only inevitable to evaluate the effects of row orientation on phtosynthesis and transpiration, but it is also important to estimate the consequences of light dynamics. Functional-structural plant modeling (FSPM) provides a tool to simulate light environment of greenhouse tomato, whereby the investigation of optimal row orientation and the effect of stomatal conductance and its dynamics on photosynthesis and transpiration become possible.
Aim of the research: Determining the optimal row orientation of greenhouse tomato with special emphasis on stomatal conductance, its dynamics, thus assimilation and transpiration, using functional-structural plant modeling.
Models, materials and methods: A coupled steady-state photosynthesis (Farquhar, von Caemmerer and Berry, FvCB) and stomatal conductance (Ball, Woodrow and Berry, BWB) model was used to evaluate the effects of row orientations on crop performance. Furthermore, the effect of light dynamics was esimated using the Vialet-Chabrand, Dreyer, Brendel (VCDB) dynamic stomatal conductance model coupled with the FvCB and BWB models.
Functional-structural plant model of greenhouse tomato was established in GroIMP 1.5, using ray tracing for light environment simulations. Data for photosynthesis, stomatal conductance and FSP model calibrations were gathered in greenhouse tomato experiment with North-South and East-West row orientations.
Results: The VCDB model calibration demonstrated that stomatal dynamics may be a significant reduction factor of assimilation. It was verified by the simulations carried out with measured irradiance data at two levels in the canopy, according to which assimilation reduction can be up to 40 % at 700 ppm CO2 concentration, compared to the potential daily carbon fixation, calculated by the steady-state coupled model. Higher CO2 concentration can signficiantly mitigate this effect, but row orientation has slight influence on it. Stomatal dynamics barely affected the transpiration output.
The FSPM results showed that North – South row orientation may provide better daily assimilation on December 23, while on June 21 and May 12, East-West row orientation may be better.
The vertical distribution of photosynthesis and transpiration did not show discrepancies between the row orientations. The diurnal pattern of assimilation demonstrated that at low solar elevation angles, the direct irradiance should reach the canopy in parallel with the rows, while at higher solar elevation angles, row orientation has weak effect on light interception.
Conclusion and recommendations: Considering the Netherlands as the location of the greenhouse, the North-West row orientation may result in better light interception in the winter at low sun elevation angles, while in the summer, the East-West row orientation may provide better performance.
According to the results, stomatal dynamics results in photosynthesis reduction at every canopy level on sunny days, but its effect is more significant at higher canopy levels, and lower at higher CO2 concentration.
Due to the limitations of the models and the calibration process, further research is necessary to improve the stomatal conductance model and the greenhouse tomato functional-structural model and to carry out validation in order to gain solid quantitative results.