Effects Of Different Led Light Qualities On Cucumber And Head Cabbage Seedling Growth, Photosynthetic Characteristics And Endogenous Hormones

Cucumber (Cucumis sativus L.) cultivar “yinpei99” and head cabbage (Brassica oleraceaL.var.capitata L.) cultivar “8398” were selected as materials. LED-T8lamp which can preciselymodulate light intensity and light quality were used as the light source. The experimentexplained effects of white, red, blue, red and blue combination light on growth and development,photosynthesis, fluorescence characteristics, the endogenous hormones levels in differentorgans and chloroplast ultrastructure of the two kinds of crop seedling. The main results are asfollows:1. The red LED light can not only improve plant biomass but also be propitious to promotethe elongation growth and leaf expansion of head cabbage seedlings. On the contrary, the blueLED light is beneficial for diameter increment, dry matter accumulation and increasing seedlingindex of cucumber and head cabbage seedlings, meanwhile, head cabbage seedlings weredwarfed. Compared to a single light source, the combination of red and blue LED light showedintegrate advantages on the growth and development of cucumber and head cabbage seedlings,in which the treatment8R/2B significantly improved stem diameter, height, dry and freshweight and seedling index of two kinds of crop.2. Under the blue LED light and a combination of red and blue light conditions, thecontent of chlorophyll and carotenoid of cucumber leaves significantly increased. What’s more,a combination of red and blue light can delay the attenuation of the chlorophyll content in thelatter. Under the red LED light treatment, the chlorophylla/b content of cucumber leavescontinuously stayed the highest, which shows the characteristics of the light-demanding plant.Unlike cucumber, the photosynthetic pigment synthesis of head cabbage seedlings leavesindicated selectivity for light qualities. A combination of red and blue light had a stimulatingeffect on photosynthetic pigment synthesis of head cabbage leaves. The red light is conduciveto the synthesis of chlorophyll b and carotenoid, moreover, it can minimize the chlorophylla/bratio, which shows characteristics of shade plants. The two kind crops under the blue lighttreatment appeared the reverse phenomena that more chlorophyll a synthesized, less carotenoidsynthesized and chlorophylla/b ratio reached maximum, which shows the characteristics of thelight-demanding plant.3. With a combination of red and blue LED light treating, the degree of openness of theblades photosystem II reaction center of cucumber and head cabbage seedlings is bigger than that of other different light treatments, and the energy which photosystem II absorbed, used inphotosynthesis, is more than that of other different light treatments. Therefore, the leavesphotosystem II function well and the photosystem II is healthier. Under8R/2B compound lighttreatment, these parameters Fv/Fm, φPS II, qP and Fv’/Fm’of two kind crops were significantlyhigher than those of treatment with the single light source. The light energy absorbed bycucumber leaves treated with red LED light and head cabbage leaves treated with blue andwhite LED light cannot be used for photosynthetic electron transport instead dissipated in formof heat energy resulting from increasing NPQ.4. In the early stage of treatment, the red light can improve the net photosynthetic rate (PN)of head cabbage seedlings, while the blue light can significantly elevate the net photosyntheticrate (PN) of cucumber seedlings. In the later stage, a combination of red and blue light canmake two kind crops leaves elevate net photosynthetic rate (PN), reduce transpiration water lossand significantly improve water use efficiency (WUE). In addition, the blue light inducedstomata opening of cucumber and head cabbage leaves, the leaves had a larger stomataconductance (GS).5. The blue LED light and a combination of red and blue LED light can significantlyimprove GA3content of cucumber stems,also in head cabbage stems and leaves. In addition,higher GA3content can promote plant height, stem diameter and leaf vertical and horizontalexpansion, and stimulate the biomass and dry matter accumulation of head cabbage. The redLED light can improve the IAAcontent in the stems and leaves of head cabbage, and the higherIAA content promoted plants bold and elongation and leaf expansion. The IAA content in thestems and leaves of cucumber is higher under compound light8R/2B conditions, which canmake shoot biomass increased. The ABAcontent of two crops is low with a combination of redand blue light treatment, which appears lowest under8R/2B treatment. The ABA content incucumber with white light treatment is lower than that with the red or blue light treatment, theresult in head cabbage shows the same. The ABA associated with GA3and IAA plays aregulatory role on plant height, stem diameter, leaf expansion, biomass and dry matteraccumulation.6. The white light was not conducive to cucumber chloroplast mature, but made headcabbage chloroplast enlarged. The red light caused excessive accumulation of chloroplast starchgrains, which inhibited the output of photosynthetic products from the leaves. Under the red light, the chloroplast photosynthetic area proportion of head cabbage was larger, thylakoid bodybattled closely. Under a combination of red and blue light, the chloroplast organization ofcucumber and head cabbage leaves had clear structure, regular shape and thick and continuousthylakoid body battlement.