Effects Of Supplemental Light Quality And Durations Of Illumination On Cucumber Seedling Growth,Photosynthetic Characteristics

The objective of this study was to evaluate the effect of lighting durations and light quality on growth and photosynthetic characteristics of cucumber(Cucumis sativus L.) seedling. The experiment was conducted in a modern greenhouse facility of Gansu Agricultural University using light-emitting diodes(LEDs). Three lighting durations(2, 4, and 8 h) of supplemental lighting applied at night were combined with six light qualities: White light(W), Red light(R), Blue light(B), a 3:7 mixture of B and R, a 2:8 mixture of B and R, and natural light as the control. Main results were concluded as follows:(1)Supplementary 7R/3B with 4 h of illumination at night can improve shoot growth and shoot DW of cucumber seedling.The height and stem diameter of cucumber seedling was also increased under this supplementary treatment. With days of supplemental treatments increased, the effect of duration and light quality treatments on the leaf area of cucumber seedling could be observed gradually. Supplementary 7R/3B with 4 h of illumination had the most positive effect on the leaf area and shoot DW compared with other treatments.(2)The result showed that the lighting durations and light qualities had significantly effect on seedling height, root diameter, root length, root surface area, root branch numbers, root activity, shoot dry weight(DW), root DW and seedling index. Significant interactions for the duration of illumination and light quality were found in affecting shoot- and root-related traits. Growth traits of cucumber were significantly higher under the supplemental 4h lighting were significantly higher than that under the 2 or 8 h supplemental lighting. Shoot- and root-related traits observed under light qualities of mixture of B and R treatments were significantly higher than that under B, R,W and natural light. Seedling height and stem diameter were 9.6cm and 3.2mm respectively. Root length, root surface area, root branch numbers, root activity under 7R/3B with 4 h of illumination were 1028.0cm plant-1?124.1cm-2 plant-1?5165.3 plant-1 and 481.9 mg g-1 h-1, respectively. Shoot and root DW were 0.41 and 0.072 g plant-1, respectively. The traits above were significantly higher than that under B, R,W with 2h and 8h of illumination and natural light. Shoot DW and root DW showed a positive relationship with root activity respectively(P<0.01). We conclude that supplementary 7R/3B with 4 h of illumination at night can increase shoot and root DW by promoting the root activity of cucumber. It built the physical foundation of sound seedling cultivation.(3)Supplemental blue lighting for 4 h prevents the senescence by maintaining high levels of anti-oxidant enzymes. Compared with natural light, supplemental lighting could significantly improve the chlorophyll a, chlorophyll b, chlorophyll content and carotenoid content of cucumber seedling, and the effect of combined light components(7R/3B and 8R/2B) for the duration of 4 h were the most significant. And that supplemental lighting could significantly improve the content of soluble protein,blue light had the greatest the content of soluble protein. Meanwhile, supplemental blue lighting for 4 h promoted significantly the contents of soluble protein and the activities of anti-oxidant enzymes(POD ? SOD ? APX and CAT). In contrast, supplemental blue lighting for 4h decreased the contents of MDA.(4)With days of supplementary treatments increased,the effect of duration and light quality treatments on chlorophyll fluorescence of cucumber seedling leaves could be observed gradually. Themaximal photochemical efficiency of PS?in the darkness(Fv/Fm), actual photochemical efficiency of PSII in the light(?PSII) and photochemical quenching(q P) under combined light components(7R/3B and 8R/2B) were significantly higher than those under blue light, red light and check. And the non photo-chemical quenching(NPQ) under combined light components(7R/3B and 8R/2B) were lowest than that of other treaments. The influence of duration and light quality on photosynthetic rate during one day appeared from 10:00 am to 16:00 pm, and peak value was observed at 12:00. Appropriate combined duration and light quality could increase leaf area and photosynthetic rate of cucumber seedling by improving the chlorophyll content and root activity.(5) Different duration and light quality had the significant effect on SPAD value of cucumber seedling. With days of supplementary treatments increased,the effect of duration and light quality treatments on SPAD value of cucumber seedling leaves could be observed gradually. We concluded that vary of SPAD value and indicated the chlorophyll content of cucumber seedling under different supplementary treatments. The SPAD value of cucumber seedling leaves was significantly increased under combined light components(7R/3B and 8R/2B), blue light, red light and white light with duration increasing. Different duration and light quality had the significant effect on chloroplast ultrastructure of cucumber seeding leaves. Number of starch grain was increased under red and blue light. Well chloroplast trastructure, rich mitochondria, clear grana and stroma lamella were observed under combined light components(7R/3B and 8R/2B).