Rapid and automated leaf net photosynthetic rate determination for numerous phosphor-converted white-LED lights of different spectral distributions

Abstract

BackgroundPhosphor-converted white LEDs (PCW-LEDs) of numerous types with different relative spectral photon-flux-density distributions (SPDs) are commercially available today. Some are regarded as promising light sources for plant factories with artificial lighting. Therefore, some methods must be developed for rapidly selecting appropriate ones from numerous types of PCW-LEDs with relevant evaluation criteria. For rapid determination of leaf net photosynthetic rates (Pn) under dozens of PCW-LED lights with different SPDs, we have developed a rapid and mostly automated Pn-quantification method.ResultsThe method uses a modified LED-artificial sunlight source system (LASS system) and a Pn-measurement system. The modified LASS system includes LEDs of 30 types with different relative SPDs: monochromatic LEDs of 27 types (426–826 nm peak wavelengths) and PCW-LEDs of three types. The system combines the LED lights to produce light with an SPD, which can accurately approximate that of any PCW-LED light at a photosynthetic photon flux density (PPFD) of 150 μmol m−2 s−1. The Pn-quantification method includes two steps: Step 1 – producing the selected PCW-LED lights; Step 2 – using the modified LASS system to supply all the produced lights automatically and successively to an identical leaf and simultaneously measuring Pn using a Pn-measurement system. We produced PCW-LED lights of 30 types at a PPFD of 150 μmol m−2 s−1 within 2.5 h. Then we individually measured the Pn of cos lettuce, red-leaf lettuce, and green-leaf lettuce (Lactuca sativa L.) plants under all produced lights in 16 h per cultivar per repetition. Results show that the mean Pn values of the cos lettuce, red-leaf lettuce, and green-leaf lettuce under the 30 produced lights were, respectively, 7.11–8.02, 5.76–7.11, and 4.83–6.17 μmol m−2 s−1 at 20 days after sowing.ConclusionsA rapid and greatly automated method was developed for successive measurement of Pn under dozens of combined lights, of which each SPD approximated that of the selected PCW-LED lights, within days, which indicates that the method can determine the Pn quickly under numerous PCW-LED lights. Consequently, it contributes to the rapid selection of PCW-LED lights performing high Pn.