Effects Of Different Light-emitting Diede Treatments On Physiological Characters,Essential Oil Content And Fresh Aroma Components Of Mentha Arvebsis

In order to improve the poor growth of aromatic plants indoors due to lack of sunlight,Mentha arvensis which is a common kind of perennial root aromatic plant of Lamiaceae was used as test material and effects of different LED light wavelength（red,blue,white）and LED light intensity(80,160,240μmol·m^-2·s^-1)on physiological characters,essential oil content and fresh aroma of Mentha arvensis were studied.Physiological character indexes of Mentha arvensis were determined after 12 weeks of light supplement.The essential oil of Mentha arvensis was extracted by hydrodistillation and analyzed by gas chromatography/mass spectrometry system.The essential oil quality was evaluated by the method of fuzzy membership function.The volatile components of the fresh plants were collected by dynamic headspace respectively,then analyzed by an automatic thermal desorption-gas chromatography/mass spectrometry（ATD-GC/MS）system.The main results were as follows:（1）Red light was the most favorable to the increase of above-ground biomass and the fresh weight of aerial part was 148.23g in group LED-R2.Blue light was the most favorable to the increase of ground biomass,root cap ratio and root vigor.The fresh weight of root,root cap ratio and root vigor were 80.27g,0.63 and 25.43mg·g^-1·h^-1 respectively in group LED-B2.Blue light was the most conducive to the increase of tap root length and the stem diameter which were 17.67cm and 3.08mm respectively in group LED-B2.Red light was the most conducive to the increase of stem length which was23.7cm in group LED-R2.The length,width,area and fresh weight of leaf in group LED-R2 were 7.00cm,4.19cm,18.67cm² and 0.33g respectively which were significantly higher than other groups.Red light was the most beneficial to the increase of chlorophyll b and carotenoid content while blue light to the increase of chlorophyll a.Red light was the most conducive to the increase of the content of soluble sugar and starch while blue light to the content of free amino acid and soluble protein.The activities of SOD,POD and CAT were significantly improved and the content of MDA was markedly decreased with the LED treatments,leading to higher resistance.（2）The results showed that experiment groups had higher content and output of essential oil and oil trichome density which were 0.86%,1.28g per basin and 28.53 per square millimeter in group LED-R3.Essential oil content and oil trichome density were significantly positive relative which proved that the oil trichome were the major oil production structure in Mentha arvensis.The content of l-menthol showed a tendency of increasing as light intensity increases.The content of l-menthol were 67.03%,67.50%and 67.84%in group LED-R3,group LED-B3 and group LED-W3 respectively.The absolute and relative content of l-menthol were significantly positive relative and the correlation coefficient was 0.9351.The results showed that 40 kinds of components were identified in the total samples while the main components of the essential oil were similar in each group.Content of more than 2%of the components were l-menthol（48.70%-65.60%）,pulegone（15.77%³3.47%）,l-menthone（7.38%¹5.46%）and isomenthone（2.53%³.91%）respectively.A higher light intensity was more beneficial to improve the quality of essential oil which in group LED-W3 was the highest and its comprehensive evaluation value was 0.84,mainly presenting a higher l-menthol level and a lower pulegone level.（3）The results showed that 66 kinds of components were identified in the total samples and 56 kinds of components were common contained in each group,mainly including terpenes,alcohols,ketones and aliphatic hydrocarbons.L-menthol,pulegone,d-limonene and isomenthol were the main aroma components and the total relative contents of these 4 components were more than 1/3 in each experiment group,obviously higher than control group.The release amounts of l-menthol,pulegone and isomenthol had a significant increase after LED treatments and showed a higher increase as the light intensity strengthened under the same type of light.The release amounts of these 3 components in group LED-R3 were 6.04,10.45 and 34.23 times respectively as high as that of control group,which showed the biggest increase as a whole.（4）In conclusion,LED treatments could significantly promote the growth of Mentha arvensis and the synthesis of related secondary metabolites.Red light of high intensity was the most beneficial to the photosynthesis,biomass,content of essential oil,etc.Blue light significantly promoted the robust growth of seedling and white light had positive effect to improve the quality of essential oil.Taking all these factors into consideration,mixing lights with intensity of 160²40μmol·m^-2·s^-1 composed of both red and blue light even other wavelength of light will be more conducive to improve the comprehensive quality of Mentha arvensis.