Effects Of Different Temperature And Shade On Aromatic Components And Photosynthetic Characteristics Of Ocimum Basilicum ‘Purple Ruffles’

Ocimum basilicum‘Purple Ruffles’ is an annual color leaf aromatic herb of the genus Labiatae.Because of its unique leaf color and aromatic volatile matter,as well as its three functions of "greening","beautifying" and "aromatization",it has great application value in landscape architecture.In this study,Ocimum basilicum‘Purple Ruffles’ was used as the experimental material to conduct the treatment tests of four different daily mean temperatures,daily mean temperatures is 15℃,20℃,25℃,30℃.and four different shading treatments,shade degrees is 0%,25%,50%,75%.through the analysis of aromatic components,leaf pigment,photosynthetic characteristics and leaf anatomical structure,provided scientific basis for landscape application of Ocimum basilicum‘Purple Ruffles’ and development of aromatic essential oil.The main results are as follows:（1）Under each daily mean temperature treatment,55 kinds of aromatic substances were detected,including 12 kinds of alcohols,30 kinds of hydrocarbons,6 kinds of esters and 2 kinds of ketones.The content of alcohol and hydrocarbon is the highest,and linalool is the main volatile component.The content of linalool reached about 20% at 15℃ and 30℃,nearly twice as high as that at 25℃.The content of eucalyptus oil alcohol is next to linalool,and the content of eucalyptus oil alcohol is higher at 15℃and20℃.Methyl eugenol is the only phenolic compound detected,but its content is high at different daily mean temperatures.Considering synthetically,the daily mean temperature of 15 ℃ is the ideal daily mean temperature for the extraction of aromatic components from Ocimum basilicum‘Purple Ruffles’.（2）The content of chlorophyll and carotenoid was higher at 25 ℃ and 30 ℃,and the content of anthocyanin was the highest at 15℃.Therefore,proper cooling measures should be taken in summer to maintain the leaves color of Ocimum basilicum‘Purple Ruffles’;The values of net photosynthetic rate,stomatal conductance,intercellular CO₂ concentration and transpiration rate were higher at 15℃ and 20℃,which indicated that the net photosynthetic rate was controlled by stomatal factors under daily mean temperature stress;When the daily mean temperature was higher than 15 ℃,the thickness of leaves increased significantly.When the daily mean temperature reached 30℃,the thickness of upper and lower epidermis decreased significantly.The thickness of palisade tissue increased significantly when the daily mean temperature was higher than 15℃,and sponge tissue decreased significantly when the daily mean temperature was higher than 20℃.（3）72 kinds of aromatic substances were detected under different shade levels,47 under 50% shade,43 under 25% shade,and only 35 under full light.There are 19 kinds of alcohols,37 kinds of hydrocarbons,7kinds of esters and 3 kinds of ketones,among which the highest content is linalool.Under full light,the content of alcohols is the highest,up to 50.90%,but the content of phenols is the lowest.The species and content of hydrocarbons and ketones were higher under 25% shading.In general,the total amount of aromatic substances is more when shading 25%,and the content of hydrocarbon compounds is increased,and the content of other compounds is well preserved,which is an ideal shading condition for extracting aromatic components.（4）The content of chlorophyll and carotenoid was the highest under light（25%）and medium（50%）shading,and the content of anthocyanin was the highest under full light.Therefore,we should try to put Viola in the sunny place to keep the best leaves color;The net photosynthetic rate,stomatal conductance,transpiration rate were the highest under full light and intercellular CO₂ concentration was the highest under heavy shade（75%）.Therefore,non stomatal factors are the main factors affecting the photosynthetic rate of Ocimum basilicum‘Purple Ruffles’ under shading treatment;With the increase of shading degree,the thickness of Ocimum basilicum‘Purple Ruffles’ leaves decreased gradually,but increased under the condition of heavy shading.The thickness of upper and lower epidermis decreased with the increase of shade,and the thickness of upper epidermis was thicker than that of lower epidermis.Because of the change of leaf thickness,palisade tissue and spongy tissue decreased first and then increased with the increase of shading degree,and in order to adapt to low light environment,palisade tissue gradually turned to spongy tissue.