The effect of humic acid on leaf morphophysiological and phytochemical properties of Echinacea purpurea L. under water deficit stress

Purple coneflower (Echinacea purpurea) is one of the most important medicinal plants used in most developed countries and drought stress is one of the most serious living stresses that reduces the quality and quantity of plant yield. Therefore, an experiment was performed in a factorial form based on a randomized complete block design during the crop year, 2014, that treatments included water deficit stress at four levels (control (non-consumption), 40, 60 and 80% of field capacity) and humic acid including four levels (zero (control), 250, 500 and 1000 mg/kg). The results showed that drought stress significantly reduced the chlorophyll, carotenoid and relative water content of the leaf and increased ion leakage, leaf burn percentage and proline content of the plant. However, acidic treatments improved plant growth and somewhat moderated the effects of drought. Three phenolic compounds, cichoric acid, caffeic acid and chlorogenic acid are the most important active ingredients in this plant. Also, cichoric acid and chlorogenic acid were increased (91.1 and 05.1, respectively) under water deficit stress. In addition, humic acid treatment increased the chlorogenic acid content. Drought stress showed a significant difference on trichome size at 1% level. However, no significant differences were observed regarding the effect of humic acid treatments on the trichome size and the diameter of the stomata. E. purpurea is recommended for growth conditions that receive average supplemental irrigation and humic acid treatments could reduce these effects of drought stress.