Effects of planting densities on the growth of lettuce (Lactuca sativa) under continuous lighting by blue, red and far-red light emitting diodes

It is shown that adding of far-red spectrum to photosynthetic active radiation (PAR) increases the growth of some leafy vegetables.
We hypothesized that adding far-red spectrum to PAR could promote the growth of plants more under continuous lighting, and in this study, we aimed to show that planting density could have interactive effects on growth promotion by continuous far-red lighting.
Lettuce ‘Green wave’ and ‘Okayama-saradana’ were used in this experiment.
After raising up seedlings in a growth chamber, lettuce plants were irradiated continuously by blue and red light emitting diodes (LED) at the photosynthetic photon flux density (PPFD) level of 150 μmol m^‑2 s^‑1. The blue and red spectrum ratio was 1:3 as PPFD level.
In adding far-red spectrum treatment, continuous far-red lighting of 27 μmol m^‑2 s^‑1 at photon flux density, were irradiated by far-red LED. All experiments were done in growth chambers.
In experiment 1, we set two different planting densities, 44.4 and 100 plants m^‑2. Furthermore, in experiment 2, lettuce plants were grown at 6 plants m^‑2 under both lighting treatments.
At 44.4 plants m^‑2, adding far-red spectrum promoted the growth of both lettuce cultivars, simultaneously the increase of leaf area was observed.
On the other hand, there was a tendency that adding far-red spectrum could increase the growth of lettuce at 100 plants m^‑2, but the difference was less.
In the case of 6 plants m^‑2 planting density level, far-red adding treatment could also tend to induce the growth promotion of lettuce plants, than under 100 plants m^‑2. From those results, growth promotion effects by far-red spectrum adding under continuous blue and red lighting could be influenced by a distance between plants bodies, and enough space for leaf extension could be required for the growth promotion by adding far-red spectrum.

IV Asian Horticultural Congress – AHC2023

W. Miyazaki, N. Fukuda, H. Yoshida

cultivar, leaf elongation, light interception, plant shape, shade avoidance

https://doi.org/10.17660/ActaHortic.2024.1404.39