Effect Of Red Light Night-break On Morphological And Physiological Characteristics Of Cucumber Seedlings

In view of the overgrowth which often occurred during the vegetable seedlingcultivating，cucumber “Jinyou No.1” was selected as experimental material in this study toresearch the effect and mechanism on controlling overgrowth of cucumber seedlings by LEDred light, to discuss the effects of LED red light treatment on growth characteristics ofcucumber seedling. The aim was to provide theoretical bases and technological guide forcontrolling overgrowth and improving the quality of the seedlings by light regulation. Themain results of the experiment were as follows:1. Based on irradiation with10μmol/(m2·s) red light of light emitting diodes(LED),cucumber seedlings were irradiated5min every2h in the growth of the dark period,whichcould significantly inhibit overgrowth of cucumber seedlings.2. The growth of hypocotyls length, plant height, length of internode and leaf area wereinhibited, health index was improved by42.4%compared to contrast, the dry matterdistributed on the ground parts was changed, the partitioning ratio of dry matter in leaf wasimproved to varying degrees, but organic matter transported and distributed to stem wasreduced significantly.3. Chla, chlb and chla+b were decreased remarkably by red light night multibreak, nonotable effects on chla/b. The net photosynthetic rate (Pn), stomatal conductance (Gs),intercellular CO2concentration (Ci) and transpiration rate (Tr) were strikingly lowered by redlight night multibreak, but water use efficiency was significantly increased.4. Fm/Fo and Fv/Fm value of cucumber leaf were raised，the quantum yield of PSII (ΦPSII), electron transport rate (ETR) and light chemical quenching coefficient (qP) werebrought down，no significant effect on non photochemical quenching (qN). Stomata length ofcucumber leaf was reduced by red light night multibreak, no obvious effect on stomata width.5. The activity of SOD, POD, CAT and APX were increased, which enhanced theresistance of cucumber seedling. Soluble sugar content in the leaf was lowered, while solubleprotein content was increased, no significant effects on the flavonoids and total phenolcontent. 6. The nitrogen content in different organs of cucumber seedlings was raised by red lightnight multibreak, significantly increased in leaf and root; the phosphorus content wasincreased in different degree, most significant in leaf; the potassium content in root and stemof cucumber seedlings were sharply increased, while significantly declined in leaf.