Potential Photosynthetic Advantages of Cucumber (Cucumis sativus L.) Seedlings Grown under Fluorescent Lamps with High Red:far-red Light
2010
Shibuya, Toshio | Endo, Ryosuke | Kitamura, Yuki | Kitaya, Yoshiaki | Hayashi, Nobuaki
To evaluate the effect of fluorescent lamps with a high red:far-red (R:FR) light on the potential photosynthesis of transplants, we investigated the photosynthetic light responses of cucumber (Cucumis sativus L.) seedlings grown under fluorescent lamps with high R:FR light (FL(H)) and compared them with the responses of the seedlings grown under metal-halide lamps (ML) that provided a spectrum similar to that of natural light and under a fluorescent lamp with low R:FR light (FL(L)). The seedlings were grown under FL(H) (R:FR = 7.0), ML (R:FR = 1.2), or FL(L) (R:FR = 1.1) at a photosynthetic photon flux density (PPFD) of 350 µmol·m–2·s–1. The gross photosynthetic rate (P(g)), quantum yield of photosystem II (phi(PSII)), and photosynthetic electron transfer rate (ETR) of the foliage leaves were then evaluated at PPFDs ranging from 0 to 1000 µmol·m–2·s–1. The photosynthetic light response of FL(H) seedlings was similar to those of sun leaves, and the responses of ML and FL(L) seedlings were similar to those of shade leaves. The P(g), ETR, and phi(PSII) of FL(H) seedlings at PPFD of 1000 µmol·m–2·s–1 was 1.38, 1.32, and 1.28 times, respectively, those of ML seedlings, and was 1.40, 1.23, and 1.22 times, respectively, those of FL(L) seedlings. The P(g) was closely correlated with ETR in each treatment. FL(H) seedlings had thicker leaf and greater chlorophyll content per leaf area than ML and FL(L) seedlings. The greater P(g) of FL(H) seedlings than in the other two groups of seedlings at high PPFD was probably the result of the improved ETR resulting from physiological and morphological changes in response to the high R:FR light.
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