2022 年 78 巻 1 号 p. 8-18
Phosphor-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 use in plant factories with artificial lighting. The leaf net photosynthetic rate (Pn) measured under PCW-LED light is an important criterion for evaluating PCW-LEDs in terms of photosynthesis performance. To ascertain Pn rapidly under dozens of PCW-LED lights having different SPDs, we have developed a rapid and semi-automated Pn-quantification method. The method uses a modified LED-artificial sunlight source system (LASS system) and a Pn-measurement system. The modified LASS system can 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. First, PCW-LED lights of 30 types at a PPFD of 150 μmol m-2 s-1 were produced using the modified LASS system within 2.5 h. We then measured the Pn of cos lettuce, red-leaf lettuce, and green-leaf lettuce (Lactuca sativa L.) plants. In a 16-h Pn measurement repetition, the modified LASS system supplied all the produced lights automatically and successively to an identical leaf of a lettuce plant. A Pn-measurement system simultaneously measured Pn under the produced light. Results show that the mean Pn values of the cos lettuce, red-leaf lettuce, and green-leaf lettuce under the 30 produced lights at 20 days after sowing were, respectively, 7.11-8.02, 5.76-7.11, and 4.83-6.17 μmol m-2 s-1. A rapid and semi-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. Results show that the system contributes to rapid selection of PCW-LED lights performing high Pn.
