ISHS Acta Horticulturae 1337: IX International Symposium on Light in Horticulture
Converting light into biomass: quantifying the conversion efficiency |
| Authors: | M.W. van Iersel, G. Weaver, R. Legendre, C. Kim |
| Keywords: | greenhouse, imaging, light emitting diodes, light interception, plant factory, supplemental lighting |
| DOI: | 10.17660/ActaHortic.2022.1337.9 |
| Abstract:
Many studies have looked at production of crops using supplemental or sole-source lighting. However, one topic that has received little attention is the efficiency with which plants convert the provided light into biomass. Given the high cost of lighting, it is important that the light be used efficiently. The biomass produced per unit light (conversion efficiency) is an overlooked measure. To optimize the conversion efficiency, it is critical to understand the contributing factors. We conducted three studies to quantify and increase the conversion efficiency. In a greenhouse study, we grew lettuce plants with supplemental LED light. All crops received a daily light integral (DLI) of 17 mol m‑2 d‑1 provided over photoperiods ranging from 12 to 21 h. We hypothesized that longer photoperiods, with lower instantaneous photosynthetic photon flux density (PPFD), would result in greater biomass, because light is used more efficiently to drive electron transport in the thylakoid membranes at lower light intensities. Longer photoperiods did indeed increase the conversion efficiency (expressed as increase in shoot dry weight/energy use by the LED lights): biomass was 43% greater with a 21-h than with a 12-h photoperiod, despite similar DLIs and energy use. A second greenhouse study quantified the biomass and conversion efficiency of 11 different lettuce cultivars, grown without supplemental lighting. The conversion efficiency (shoot dry weight /incident light) was higher for green-leaf than for red-leaf lettuce cultivars, likely because the presence of anthocyanins can reduce photosynthesis. A third study, with white and far-red LEDs in a growth chamber, looked at the effects of PPFD and far-red light on lettuce growth and conversion efficiency. The conversion efficiency (shoot dry weight/incident light) increased with increasing PPFD and decreased with increasing far-red light. Combined, these studies show that supplemental lighting can be manipulated to increase the conversion efficiency, through effects on plant morphology and/or physiology. This can increase the cost-effectiveness of supplemental lighting. | |
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