Plant Stress (Sep 2024)
Unravelling the impact of drought and salt stresses on Thymus pannonicus: Morpho-physiological and biochemical insights
Abstract
This research assesses the effects of drought and salt stresses applied individually or in combination on Thymus pannonicus, a resilient perennial herb native to the Pannonian vegetation region. Our experiment aimed to comprehensively evaluate morphological, physiological, and biochemical parameters of the thyme subjected to two levels of soil water capacity (SWC) - 70 % (control and salt stress) and 40 % (drought stress and combined stresses) - along with two salinity levels, 0 mM NaCl (control and drought stress) and 60 mM NaCl (salt stress and combined stresses). The plants exhibited significant responses to all the studied parameters under 40 % SWC in both treatments, demonstrating notable reductions in shoot and root parameters. In contrast, salt treatment at 60 mM had a minimal impact on growth. A stability in photosynthetic pigment composition was observed in all treatment, whereas a notable decrease (p < 0.05) in relative water content was seen in drought-stressed treatments compared to the to the control. Essential oil contents were higher in the control (0.91 ml/100g DW) but significantly declined (p < 0.05) under drought stress and combined stresses conditions (0.49 ml/100g DW and 0.53 ml/100g DW respectively). Particularly, the GC-MS analysis revealed a significant decrease (p < 0.05) in thymol and carvacrol content for the drought-stressed treatments. Substantial reductions were evident for the total polyphenol concentration and antioxidant capacity under the combined stress treatment, measuring 101.49 mg GAE/g DW and 106.57 AAE/g DW, respectively. Interestingly, the HPLC analysis indicated the highest levels of rosmarinic acid and caffeic acid in the drought-stressed treatment, while the lowest ones were recorded in the combined stress treatment. These findings indicated the responses of Thymus pannonicus to environmental stressors, emphasizing the need for further investigations for a comprehensive understanding of salinity effects.
