Effects Of Different LED Light On The Growth And Physiological Characteristics Of Pioneer Orange And Tangerine Seedlings

In recent years,the demand for virus-free seedlings has increased sharply due to the spread of the disease.In order to ensure the quality and safety of nursery stocks to cultivate large seedlings,the nursery units will extend the cultivation time of the seedlings in the net room,especially in Chongqing,Sichuan and other domestic key citrus seedling nursery areas where the sunshine hours and the sunshine intensity are both insufficiently severe.Prolonged,so fill light has become an important technology choice.The new energy-saving light source light emitting diode（LED）light source has the advantages of adjustable spectrum,high light utilization efficiency,high power conversion efficiency,good controllability,and environmental protection,and is more suitable for replacing a traditional artificial light source as a light-filling lamp for plants.The effect of LED light on the growth and development of citrus has not been reported.Oranges and broad-leaved citrus are the most important cultivated species in citrus fruits.Both production and area account for more than 80%of the global cultivation area of citrus.In this paper,seedlings of Citrus sinensis Osbeck and C.tangerine Hort.ex Tanaka were used as experimental materials,and 6 types of LED light treatment were used[red light,blue light,red blue 1:1（RB1:1）,red blue 4:1（RB4:1）,red yellow blue 4:1:1（RYB4:1:1）and white light（W）]and fluorescent lamp（FL）treatment were used as controls to count and measure Pioneer Orange and Tangerine seedlings.The phenotype,biomass,chlorophyll content,photosynthetic characteristics,respiration rate,soluble sugar content,starch content,soluble protein content,antioxidant enzyme activity,and peroxide content of Pioneer orange and Tangerine seedlings were counted and measured.The effects of different LED light quality and different light intensity on the growth and development,photosynthetic characteristics and antioxidant capacity of Pioneer orange and Tangerine seedlings were studied.In order to screen out the suitable light quality for the growth and development of Pioneer orange and Tangerine seedlings,the phenotype,biomass,chlorophyll content and photosynthetic characteristics under the four different light intensities(50μmol·m^-1·s^-1,100μmol·m^-1·s^-1,150μmol·m^-1·s^-11 and 200μmol·m^-1·s^-1)were investigated.1.Effects of different light qualities on seedlings of Pioneer orange and Tangerine seedlings:（1）Compared with fluorescent lamps,red light promotes stem width,root length and leaf area of pioneer orange and red orange seedlings and reduces plant height and leaf number;blue light also promotes stem width,root length and leaf thickness of Pioneer orange and Tangerine seedlings.Function,but reduce plant height and leaf area.It shows that the red and blue monochromatic light effects on the growth morphology of Pioneer orange and Tangerine seedlings are mainly focused on the impact on the leaves.At the same time,monochromatic red and blue light are not conducive to the growth of Pioneer orange and Tangerine seedlings compared to composite light.Treatment of RB4:1 was most beneficial to the morphology of Pioneer orange seedlings,which promoted plant height,stem width,leaf area,leaf thickness and root length of Pioneer orange seedlings;treatment of RB1:1 and W was beneficial to the morphology of red orange seedlings.Upon completion,the indicators of stem width,root length and leaf thickness of red orange seedlings were significantly increased.It shows that Pioneer orange and red orange seedlings have different growth morphology responses to composite light.（2）Monochromatic light affects photosynthetic characteristics of Pioneer orange and Tangerine seedlings.Blue light is more conducive to the increase of photosynthetic rate（Pn）,stomatal conductance（Gs）,transpiration rate（Tr）and intercellular CO₂concentration（Ci）of Pioneer orange and Tangerine seedlings than red light.And the chlorophyll content of blue light is higher than that of red light.However,the photosynthetic rate of monochromatic blue light is significantly lower than that of high ratio red and blue light.Compared to control FL,the composite light RB1:1,RB4:1 and RYB4:1:1 significantly promoted the increase of Pn,Gs and Tr in Pioneer orange and Tangerine seedlings,and significantly reduced Ci.It was shown that the high proportion of red and blue light compound light promoted the photosynthesis of young Pioneer orange and Tangerine seedlings.（3）Red light superoxide dismutase（SOD）,catalase（CAT）activity and membrane superoxide（MDA）content and hydrogen peroxide（H₂O₂）content in Pioneer orange and red orange seedlings were higher than blue light.This shows that compared to blue light,the leaves of Pioneer orange and red orange seedlings under red light are vulnerable to damage.The composite light of each LED increased the activity of SOD and POD in the leaves of Pioneer orange seedlings,and decreased the CAT activity,MDA and H₂O₂ content.The LED complex light increased the SOD activity,the CAT activity and the H₂O₂ content of the seedlings of Tangerine,and the POD activity decreased significantly under the composite light RB1:1,and the MDA content of the composite light RB4:1 was higher than that of the fluorescent lamp.The results showed that each composite light treatment improved the resistance of Pioneer orange seedlings and was not susceptible to over-oxidation injury,while compound light RB4:1 was not conducive to the growth of Tangerine seedlings and was vulnerable to over-oxidation..（4）The red light is beneficial to the material accumulation of the seedlings of Pioneer orange and Tangerine,as well as the material distribution of the aerial part and the underground part;and the content of soluble sugar and starch is significantly higher than that of blue light under the red light.The content of each part of the Pioneer orange seedlings of the composite light RB1:1 and RB4:1 was higher than that of the fluorescent lamp,while the composite light RYB4:1:1 only increased the content of the underground part of the Pioneer orange;the composite light RB1:1,RYB4:1:1 and W significantly increased the material content of each part of Tangerine seedlings,but the material accumulation of the composite light RB4:1 was significantly lower than that of the fluorescent lamp,further indicating that the composite light RB4:1 is not suitable for the growth of Tangerine seedlings.（5）A comprehensive analysis of the membership functions of the 14 indicators that combined the morphology and physiological characteristics of the Pioneer orange and orange seedlings revealed that the suitable LED light quality for Pioneer orange seedlings was a red-blue 4:1 composite light,while the seedlings of red orange were suitable for growth.The LED light quality is red-blue 1:1 composite light.2.Effects of different light intensities on seedlings of Pioneer orange and Tangerine seedlings:（1）The morphology of Pioneer orange and Tangerine seedlings under LED red-blue complex light conditions is also affected by light intensity.The plant height and whole plant leaf area of Pioneer orange seedlings showed a downward trend with the increase of the light intensity of LED composite light RB4:1,and the plant height,root length,leaf area and leaf area of the whole plant were all in the LED composite.Light RB4:1appears when the light intensity is 200μmol·m^-2·s^-1.The maximum value of each morphological index of Tangerine seedlings appeared when the LED complex light RB1:1 light intensity was 100μmol·m^-2·s^-11 and 150μmol·m^-2·s^-1.The RB1:1 light intensity of the LED composite light suitable for morphology is between100μmol·m^-2·s^-11 and 150μmol·m^-2·s^-1.（2）The light intensity of 100μmol·m^-2·s^-11 to 150μmol·m^-2·s^-11 of LED red-blue composite light is the optimal light intensity range for photosynthesis of Pioneer orange and Tangerine seedlings.The Pn and Gs of seedlings of Pioneer orange and Tangerine seedlings in light intensity of 100μmol·m^-2·s^-11 and 150μmol·m^-2·s^-11 light intensity were higher than 50μmol·m^-2·s^-11 and 200μmol·m^-2·s^-1.However,the Ci values of Pioneer orange and Tangerine seedlings under light intensity of 100μmol·m^-2·s^-11 and150μmol·m^-2·s^-11 were lower than 50μmol·m^-2·s^-11 and 200μmol·m^-2·s^-11 light intensity.At the same time,the contents of Chla,Chlb and Car in seedlings of Pioneer orange and Tangerine seedlings at 50μmol·m^-2·s^-1,100μmol·m^-2·s^-11 and 150μmol·m^-2·s^-11 light intensity were higher under the light intensity of 200μmol·m^-2·s^-1.（3）The effects of four light intensities on the material distribution of Pioneer orange and Tangerine seedlings were somewhat different.The fresh weight indexes of root,stem and leaf of Pioneer orange and Tangerine seedlings in 100μmol·m^-2·s^-11 and150μmol·m^-2·s^-11 were significantly higher than those of 50μmol·m^-2·s^-11 and200μmol·m^-2·s^-11 intensity treatment.At 100μmol·m^-2·s^-11 and 150μmol·m^-2·s^-1,the dry weight index of Tangerine was also greater than 50μmol·m^-2·s^-11 and 200μmol·m^-2·s^-1.However,there was no significant difference in dry weight indicators of the roots,stems and leaves of Pioneer orange seedlings under the light intensity treatment of LED composite light RB4:1.（4）A comprehensive analysis of membership functions was performed based on the 11indicators including morphology,biomass,and photosynthetic characteristics of Pioneer orange and Tangerine seedlings.It was concluded that the LED complex light RB4:1 of Pioneer orange seedlings had an optimum light intensity of 100μmol·m^-2·s^-1.The LED composite light RB 1:1 light intensity for growth of the optimum red orange seedling is also100μmol·m^-2·s^-1.