A functional-structural plant model of greenhouse-grown cucumber under LED lighting

Cucumber plants grown in high-wire production systems can be light deficient in the median zone of the crop. This zone contains leaves exhibiting a high photosynthetic activity; however, due to shading by upper leaves the photosynthetic potential of these leaves may not be fully expressed. Increasing the light level locally in this zone using interlighting can remedy this. Furthermore, fruit growth is correlated with fruit temperature and the amount of absorbed radiation. Previous work has shown that growth rate of shaded fruits could not be sufficiently modified by local heating. In the present work, we are aiming at an optimization of light microclimate around the plant, by installation of additional lighting, and improved management of LAI. Light penetration into the canopy and the optimal LAI are not well-known in high-wire cucumber production. By using a functional-structural plant modelling (FSPM) approach, we are able to simulate plant architecture as well as the associated light penetration into the canopy in 3D and at a high spatial resolution, as well as the change in stem architecture due to the high-wire management. The objective of the model is to help finding an optimal LAI for greenhouse cucumber production (as a function of the position, orientation, intensity and spectra installed lamps) and a specific position (height in the canopy, orientation, installation) of the LEDs adapted to production requirements. In the cucumber FSPM, the plants are modeled at two scales (organ and plant). Apart from plants, greenhouse, the sky and the sun, and in particular the LED panels with their spatial positions and orientations are modeled, while a light model computes the light intercepted by leaves at each step. The model presented in this paper simulated two scenarios, with and without LED, which yielded the temporal dynamics of some state variables, such as leaf area or absorbed light.