Determination of the effect of foliar humic acid application on plant development and biochemical parameters of pepper plant (capsicum annuum L.) under water stress conditions

Plants grow and develop normally under favorable environmental conditions. However, environmental stress factors can negatively impact their growth. These stresses are generally categorized as either biotic or abiotic. Among the abiotic stresses, water stress is one of the most prevalent and significantly affects plant productivity, growth, development, and metabolic defense mechanisms. When exposed to water stress, plants activate various defense mechanisms to adapt to dry conditions. In this study, pepper plants were treated with different water stress (control; 100% pot moisture capacity (field capacity), 80% of the amount of water given to the control, 40% of the amount of water given to the control, 20% of the amount of water given to the control) and 50 ppm humic acid (HA) was applied to the leaves as a curative. The plant development parameters (plant height, plant fresh weight, plant dry weight, root fresh weight and root dry weight, electrical leakage (ES) and biochemical parameters (chlorophyll a, chlorophyll b, proline, lipid peroxidation (MDA), hydrogen peroxide (H2O2), antioxidant enzymes (POX and CAT), and mineral contents (N, P, K, Ca, Mg, Fe and Zn) were examined. The results indicated a decrease in plant growth parameters as water stress increased. However, plants treated with HA showed improved growth compared to untreated plants under similar stress conditions. Biochemical responses to water stress were also observed; levels of proline, MDA, and H2O2 increased compared to the control. These results suggest that defense mechanisms were activated in response to water stress, helping mitigate its adverse effects. Moreover, the foliar utilization of HA enhanced nutrient uptake and significantly contributed to improved plant development.