Effects of water deficit stress and fertilizer sources on morphological characteristics and phenolic compounds in medicinal plant purple coneflower (Echinacea purpurea L.)

The experiment was conducted to study the effects of water deficit stress and fertilizer sources on characteristics of Echinacea purpurea L., in a split plots design with three replications at the research farm of Faculty of Agriculture, Ferdowsi University of Mashhad, Iran during two years of 2016 and 2017. Irrigation consisted of three levels of non-stress (control), moderate, and severe moisture stress and fertilizer consisted of eight levels of complete fertilizer (NPK), vermicompost, humic acid, humic acid+NPK, humic acid+vermicompost, NPK+vermicompost, NPK+vermicompost+humic acid, and non-use of fertilizer (control). The single effects of deficit irrigation and fertilizer treatments were significant (p≤0.01) on the stem height, number of stems and flowers plant-1, biomass dry weight, total chlorophylls a and b, and proline content; however, their interaction effects were only significant (p≤0.01) on phenolic compounds of the leaves. In relation to the single effects of irrigation treatments, the highest height and number of stems, number of flowers plant-1, and biomass dry weight was observed in non-water stress treatments and the lowest amount of these characteristics was observed in severe water stress treatments. The highest and lowest proline content was shown in severe and non-stress treatments, respectively, and the highest and lowest total chlorophylls a and b were obtained in non-stress and severe moisture stress, respectively. Regarding the single effects of fertilizer treatments, there was no significant difference in plant height between fertilizer levels; however, all of them had a significant difference with control treatment (no fertilization). The difference between fertilizer treatments was significant in the number of stems and flowers plant-1 and biomass dry weight. The highest number of stems and flowers was obtained in humic acid+vermicompost treatment and the highest amounts of biomass dry weight were obtained in vermicompost+NPK treatment. The lowest values of these traits were observed in control (non-fertilization). The highest and lowest amounts of total chlorophylls a and b were obtained in vermicompost+NPK and control treatments, respectively, and the highest and lowest proline values were obtained in control and vermicompost treatments, respectively. The highest phenolic compounds were observed in humic acid+vermicompost+NPK and humic acid+NPK treatments, both of which under severe moisture stress, and the lowest one in non-stress and non-fertilization (control) treatment.