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ISHS Acta Horticulturae 1134: VIII International Symposium on Light in Horticulture

Using chlorophyll fluorescence to control lighting in controlled environment agriculture

Authors:   M.W. van Iersel, E. Mattos, G. Weaver, R.S. Ferrarezi, M.T. Martin, M. Haidekker
Keywords:   biofeedback, electron transport rate, light emitting diodes, photosynthesis, quantum yield
DOI:   10.17660/ActaHortic.2016.1134.54
Supplemental lighting is often needed for crop production in controlled environments. Such supplemental lighting can be expensive and inefficient. Chlorophyll fluorescence is a valuable tool for monitoring light use efficiency in plants and can be used to determine the quantum yield of photosystem II (φPSII) and the electron transport rate through photosystem II (ETR). Combining chlorophyll fluorescence measurements with light emitting diodes (LED), whose intensity can be easily and automatically adjusted, provides an unexplored opportunity to control lighting based on the physiology of the plants. We describe here how a chlorophyll fluorescence-based biofeedback system can be used to maintain steady φPSII or ETR by adjusting the duty cycle of the LEDs. Although the biofeedback system was capable of maintaining a stable φPSII of lettuce (Lactuca sativa), it did so by gradually down-regulating the photosynthetic photon flux density (PPFD), resulting in very low ETR and thus low photosynthetic rates. Maintaining stable ETR appears to be more promising: the biofeedback system was capable of maintaining a range of different ETRs over 12-h periods. To do so, the PPFD had to be gradually upregulated, because of a steady decrease in φPSII. This decrease in φPSII is likely due to an upregulation of non-photochemical quenching and possibly photoinhibition induced by the saturating pulses from the fluorometer. The next phase in this research is to determine how to use the biofeedback system to optimize energy efficiency and growth. Optimal control algorithms for biofeedback of lighting may need to take into account φPSII, ETR, and non-photochemical quenching.

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