Chlorophyll fluorescence as a biological feedback signal -for optimized plant growth conditions and stress diagnosis
Doctoral thesis, 2021
We found that steady-state ChlF have a strong correlation with short term photosynthesis and can be used for estimation of relative efficiency of different LED colors with respect to each other. We did not find significant changes in the relative efficiencies when light intensity or spectrum was changed, as was initially hypothesized. However, the method can still be applicable for spectrum calibration, as the efficiencies of different LED colors vary individually as the diodes degrade with time and they also vary to different degree depending on the operating temperature.
Experiments on abiotically stressed plants (drought, salt, and heat) showed that variations in the dynamics of the ChlF signal can be used to classify plants as healthy or unhealthy. Experiments with the root infection Pythium ultimum indicated that severe infection is detectable. This is promising as it by its nature is hard to detect without harvesting. More research is needed though, to statistically verify if this, and other biotic stress factors can be detected, and if so, how severe the infection must be.
Fast ChlF gain, defined as the amplitude of the ChlF signal caused by light pulses with a high frequency and a low intensity, was found to have a concave shape with respect to light intensity. Furthermore, the light intensity corresponding to the maximum of the fast ChlF gain coincide with the light level where the photosynthetic rate starts to saturate, which in some sense can be regarded as an optimal light level for efficient growth. Hence, we suggest the use of an extremum seeking controller to force the light intensity level to this point and demonstrates how this works in a simulation study.
powdery mildew Podosphaera aphanis
greenhouse lighting control
Chalmers, Electrical Engineering, Systems and control
Stress Detection Using Proximal Sensing of Chlorophyll Fluorescence on the Canopy Level
AgriEngineering,; Vol. 3(2021)p. 648-668
Relation between Changes in Photosynthetic Rate and Changes in Canopy Level Chlorophyll Fluorescence Generated by Light Excitation of Different Led Colours in Various Background Light
Remote Sensing,; Vol. 11(2019)
Using chlorophyll a fluorescence gains to optimize LED light spectrum for short term photosynthesis
Computers and Electronics in Agriculture,; Vol. 142(2017)p. 224-234
LED spectrum optimisation using steady-state fluorescence gains
Acta Horticulturae,; Vol. 1134(2016)p. 367-374
Linnéa Ahlman, Daniel Bånkestad, Torsten Wik. Tracking optimal plant illumination using proximal sensed chlorophyll fluorescence gain
There is an ongoing change in greenhouses and indoor growing facilities, from the use of traditional high pressure sodium lamps, to light emitting diodes (LEDs). This enables tuning and optimization of both light intensity and light spectrum, which opens for an energy saving potential not possible otherwise. Such controllable lamps can also be used to generate light excitations, which cause changes in the plants' ChlF that depend on the state of the plant. We have conducted such experiments on different plant species, to evaluate if and how ChlF, measured on canopy level, can be used as a biological feedback signal for spectrum optimization, stress detection, and for light intensity optimization.
Our experimental results indicate that feedback of the steady-state ChlF signal can be used for estimation of relative efficiencies of different LED colors for plant growth. This can be used for spectrum calibration to minimize energy consumption if the efficiencies vary over time. Furthermore, we found that the dynamics in the ChlF signal can be used for classification of healthy or stressed plants, for abiotic stress factors (drought, salt, and heat) and possibly also for biotically stress (root infection Pythium investigated). Finally, the amplitude of the ChlF signal, caused by light pulses with a high frequency and a low intensity, was found to have a concave shape with respect to light intensity, with the maximum corresponding to what can be regarded as an optimal light intensity. We suggest the use of an extremum seeking controller to force the light intensity level to this point.
The Swedish Foundation for Strategic Environmental Research (Mistra) (MI-004), 2012-01-01 -- 2015-12-31.
Growth tracking and light optimization in greenhouse
VINNOVA (2020-04975), 2021-04-01 -- 2022-12-31.
Ny metod för biotisk stressdetektering i hortikulturell produktion
Statens jordbruksverk (2018-2390), 2019-11-01 -- 2021-12-31.
Areas of Advance
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5028
KB-salen, Kemigården 4, and online.
Opponent: Prof. Per-Olof Gutman, Faculty of Civil and Environmental Engineering, Technion - Israel Institute of Technology