Chlorophyll fluorescence as a biological feedback signal -for optimized plant growth conditions and stress diagnosis
Doktorsavhandling, 2021

The use of light emitting diodes (LEDs) instead of traditional high pressure sodium lamps, in greenhouses and indoor growing facilities, enables tuning and optimization of both light intensity and light spectrum. This opens for an energy saving potential not possible otherwise. Furthermore, such controllable lamps can be used to generate low intensity light excitations, which cause changes in the plants' chlorophyll fluorescence (ChlF). Analysis of these changes can then be used for plant diagnosis. We have conducted such experiments on plants to evaluate if and how proximal sensed ChlF, measured on canopy level, can be used as a biological feedback signal for spectrum optimization, stress detection, and for light intensity optimization.

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.

Fluorescence gain

ESC

classification

lemon balm

indoor farming

lettuce

abiotic stress

LED

Pythium ultimum

dynamics

cucumber

basil

greenhouse lighting control

powdery mildew Podosphaera aphanis

strawberries

light spectrum

biotic stress

KB-salen, Kemigården 4, and online.
Opponent: Prof. Per-Olof Gutman, Faculty of Civil and Environmental Engineering, Technion - Israel Institute of Technology

Författare

Linnéa Ahlman

Chalmers, Elektroteknik, System- och reglerteknik, Reglerteknik

Stress Detection Using Proximal Sensing of Chlorophyll Fluorescence on the Canopy Level

AgriEngineering,; Vol. 3(2021)p. 648-668

Artikel i vetenskaplig tidskrift

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

Artikel i vetenskaplig tidskrift

LED spectrum optimisation using steady-state fluorescence gains

Acta Horticulturae,; Vol. 1134(2016)p. 367-374

Artikel i vetenskaplig tidskrift

Linnéa Ahlman, Daniel Bånkestad, Torsten Wik. Tracking optimal plant illumination using proximal sensed chlorophyll fluorescence gain

Most of the light absorbed by a plant is used for photosynthesis, but part of it is reemitted. Some of the reemission is light in the red and far-red regions, which is called chlorophyll fluorescence (ChlF). Normally, this cannot be detected by the naked eye, but it can be detected by optical sensors and used for plant diagnosis.

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.

Intelligent Light

Stiftelsen för miljöstrategisk forskning (Mistra) (MI-004), 2012-01-01 -- 2015-12-31.

Produktionsstyrning och ljusoptimering i växthus

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.

Drivkrafter

Hållbar utveckling

Styrkeområden

Energi

Ämneskategorier

Reglerteknik

Signalbehandling

ISBN

978-91-7905-561-5

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5028

Utgivare

Chalmers tekniska högskola

KB-salen, Kemigården 4, and online.

Online

Opponent: Prof. Per-Olof Gutman, Faculty of Civil and Environmental Engineering, Technion - Israel Institute of Technology

Mer information

Senast uppdaterat

2021-10-03