1. Introduction-Hypothesis
Effects of LED lighting on seedlings growth of Fraxinus ornus L. Sofia Smirnakou1 and Kalliopi Radoglou2 1Forest Research Institute, Demeter, Thessaloniki, Greece 2Dept of Forestry and Management of the Environment and Natural Resources Democritus University of Thrace (DUTH), Orestiada, Greece :
Results & Discussion   a a b A B B
Introduction-Hypothesis
LED technology is a promising light source that contributed to the field of knowledge and understanding of the plant’s responses to different radiations and light intensities on their growth and development in controlled environments.
Providing combined advantages such as high energy-conversion efficiency, small volume, longer life, specific wavelength, light intensity/quality adjustable and low thermal energy output.
In this study we identified the effects of LED light spectra G2, AP67, AP67-ARCH, NS2 (Valoya) or Fluorescent light (FL) on seedlings of manna ash (Fraxinus ornus L.) on growth and seedling quality.
Aim: Plant specification cultivate-protocols under the optimal spectrum for growth.
Innovation: determining LEDs with continuous spectrum quality specific effects regulating growth and physiology of forest tree species. a b a a
Figure 1. Differences among means in shoot height and root length under different light treatments for the seedlings of F.ornus at the end of the 5th week. Vertical bars represent the standard deviation. Values followed by a different letter are significantly different (Bonferroni test, p=0.05)
Figure 2. Differences among means in number and colour of leaves under different light treatments for the seedlings of F.ornus at the 5th week. (Values followed by a different capital letter are significantly different for the number of leaves (Bonferroni test, p=0.05)
Material-Methods  
Seed collection & Pretreatment
Vertiskos mountain (480 m a.s.l ), collected in 2011
Seeds were soaked for 24hrs
Cold stratification for 3 months at 3-50C and placed in phytotron chamber till germination
Photo 1.a. Pre-germinated seeds
Figure 3. Height growth rate of F.ornus seedlings under different light treatments during the 5 week experimental period. Vertical bars represent the standard deviation
Experimental design
Pregerminated seeds were placed in mini-plug trays (104 cells; 33X33X45 mm; 40 mm/h; 27 cc) (QPD 104 QuickPot by HerkuPlast-Kubern, Germany)
Growing medium: Stabilized peat (pH , very little Borium) (Preforma PP01, Jiffy® Products, Norway)
Growth chambers conditions: 14 hrs photoperiod, 150 μmol m-2 s -1 photosynthetic photon flux density (PPFD), 70%, air relative humidity (RH) and a 22°C/18°C day/night temperature, for 5 weeks. Watering: twice a day by automatic sprinklers
LEDs : mixture of ultraviolet, blue, green, red, far-red and infra-red in various percentages
G2 (B:7.6% G:2.4% R:63.6% FR:19.5% INFR:6.8%),
AP67 (B:12.7% G:15.8% R:52.7% FR:13.9% INFR:4.7%)
AP67-ARCH (B:15.7% G:25.2% R:44.8% FR:10.6% INFR:3.6%)
NS2 (UVC: 1.8% B:22.3% G:40.6% R:33.1% FR:1.6% INFR:0.5%)
FL (1 X 30W, 230 V, 50Hz) a a a b
Figure 5. Differences among means in R/S ratio under different light treatments for the seedlings of F.ornus at the end of the 5th week. Vertical bars represent the standard deviation. Values followed by a different letter are significantly different (Bonferroni test, p=0.05)
Figure 4. Differences among means in dry weight leaves, shoot and roots under different light treatments of F.ornus seedlings at the end of the 5th week
After 5 weeks, shoot height under the G2 and FL light was found significantly higher only compared to the NS2 light, while no differences were observed in root length irrespective of the light spectrum, although the root length was double in comparison to the shoot height. G2 light has the highest red radiation percentage of all tested light treatments, while the NS2 light has the highest blue radiation percentage. Red radiation found to be responsible for stem elongation whereas blue inhibits it and plants tend to be more compact.
Greater number of leaves was formed for seedlings grown under LEDs, especially under the G2 and AP67 lights, while the lowest number was formed under the FL light treatment. However at the 5th week G2 light apart from the FL light, found to be significantly different from the NS2 light treatment. Significant difference for the leaf colour of F.ornus seedlings was found only for the AP67-ARCH light compared to all light treatments that characterized as light-green according to the established colour rating. In contrast seedlings under FL, NS2 and AP67 light treatments had more dark-green leaf colour , specifically at the 5th week of the experimental period.
Adjustments on the morphological state of F. ornus seedlings responded relatively to time and light treatment. Height growth rate differences are explained by the difference of G2 and FL compared to AP67, AP67-ARCH and NS2 light treatments after the 2nd and 3rd week in growth chambers.
Results of the dry weight biomass showed distinct growth responses to the different light treatments. Significant higher values were found in DWL, DWS, DWR, for seedlings grown under the G2 light. The lowest values among all light treatments were found for the FL light. G2 light also differ significantly from the NS2 and AP67-ARCH lights for the DWL and only from the NS2 for the DWS among LEDs.
AP67-ARCH, NS2 and AP67 lights differed significantly from the FL for the R/S ratio. No significant difference found between G2 and FL light nor the rest of LEDs. The larger leaves in number and dry weight under the G2 light allowed greater light interception which may had led to significant increase in biomass.
Photo 2. a. Growth chambers
Photo 2. b. Fraxinus ornus seedlings under different light treatments
Seedling measurements
During the 5 weeks: Number of leaves and visual evaluation of the leaf colour rating as 1=pale (R:255, G:255, B:204)
2=light green (i) R:153, G:204, B:0, ii) R:102, G:204, B:0 and iii) R:102, G:153, B:0
3=dark green (i) R:0, G:100, B:0, ii) R:85, G:107, B:47 and iii) R:110, G:139, B:61 (Fig.2)
Height growth rate was measured (Fig.3)
At the end of 5 weeks: 10 randomly selected seedlings were measured for the stem height (mm) and the root length (mm) (Fig. 1)
Dry weight (g), of the leaves, stems and roots (Fig. 4)
Root/shoot ratio (Fig.5)
   Conclusion 
Seedlings grown under LED lights promoted the optimal growth traits of manna ash seedlings in contrast to Fluorescent light where reduction in dry weight matter suggest that light quality can alter growth, decrease the mean weight and lower its quality as planting stock material.