Investigation of Morpho-Physiological Properties of Peppermint (Mentha piperita L.) Affected by Carbon Sources of Ethanol and Methanol

 Nowadays, spraying method is used in plant nutrition to optimize the use of chemical fertilizers and reduce environmental hazards. With the foliar solution, the elements are quickly transferred to the plant and delivered to the branch, leaf, or fruit. Surveys show that increase performance per unit area is one of the most important things that has attracted the attention of many researchers. The first requirement for high performance is high dry matter production per unit area. Some experiments have shown that increasing the amount of carbon dioxide in the air can increase yield, accelerate flowering and accumulate carbohydrates in plants. One of the solutions to increase carbon dioxide concentrations in plants is to use compounds such as ethanol and methanol. Therefore feeding plants with alcohols such as ethanol and methanol as carbon sources is one of the appropriate methods to increase their quantitative and qualitative properties.
 Due to the importance of peppermint (Mentha piperita L.) in the production of valuable secondary metabolites, and also the effect of ethanol and methanol on some morphological and physiological parameters of this plant, a pot experiment was conducted in factorial based on completely randomized design with three replications in the research greenhouse of Shahed University in 2018. Foliar treatments included different concentrations of 0, 15, 30 and 45% ethanol, methanol and combine them that was done in three stages. The studied traits were plant height, number of leaves per plant, biological yield, chlorophyll a, chlorophyll b, total chlorophyll, carotenoid, flavonoid, essential oil percentage, essential oil yield and protein percentage. Data analysis was performed using SAS statistical software (version 9.2) and mean treatments were compared by LSD test. Also charts were drawn by excel software.
 The results showed that the simple effects of ethanol and methanol on plant height, biological yield, flavonoid content, essential oil percentage, essential oil yield and protein percentage were significant but their interactions were not significant. Ethanol 45% had the most effect on percentage and yield of essential oil and protein percentage. But the use of 15% ethanol treatment had the highest value in other traits (plant height, total phenol and flavonoids), which was at a statistical level with 45% methanol treatment. Also interaction between ethanol and methanol on leaf number per plant, chlorophyll a, chlorophyll b, total chlorophyll and carotenoid was significant at 1% probability level. The highest number of leaves per plant and chlorophyll a (29.55 µg/g fresh leaf weight) was observed in the combination of 15% ethanol and 15% methanol, while the highest amount of chlorophyll b (20.86 µg/g fresh leaf weight) and total chlorophyll (49.85 µg/g fresh leaf weight) was related to the combined application of 15% ethanol and 45% methanol.
 
Foliar spraying is one of the methods of fertilization and supply of nutrients to plants that due to high absorption rate nutrients can be made available to plants in the shortest time. The results of this study showed that all the studied traits were significantly affected by one or more of the ethanol and methanol treatments. Therefore, the foliar application of ethanol and methanol as carbon sources has an important role in improving the qualitative and quantitative parameters of peppermint.