Multivariable System Identification of CO₂ Uptake in Lettuce as Affected by the Pulsed Light Illumination

Abstract

In our previous study, we identified the effect of the pulsed light illumination on the photosynthesis of Okayama Saradana with an one input-output system model and showed the possibility of saving electrical power by the application of the new artificial light source in the plant factory.
Photosynthesis of plant is also affected by CO₂concentration besides the pulsed light. So, the dynamic characteristics of the photosynthesis to CO₂concentration is also important to the analysis of the cultivating processes in the plant factory.
In this paper, we used a multivariable system model to estimate the effect of the pulsed light illumination on the photosynthesis of Okayama Saradana. Pulsed light illumination and CO₂concentration were taken as two input signals and the net CO₂uptake as the output signal. Impulse responses of net CO₂uptake to the two inputs were estimated. From the simulation, we got the same result to that of the one input-output system model discussed in our previous study that the net CO₂uptake of the plant under the illumination of low duty ratio of the pulsed light could be increased if CO₂concentration of the environment is increased.
Furthermore, we discussed the differences between the result from the one input-output system model and the multivariable system model. It seems that the one input-output system model could not give a reasonable result when CO₂concentration had great change as to ±50 ppm, but the multivariable system identification could do.
Plant and environments make up a very complicated system, in which many factors are included. We think that the multivariable system identification is a powerful method to analyse this system.