Arbuscular mycorrhizal fungi inoculation improve essential oil and physiological parameters and nutritional values of Thymus daenensis Celak and Thymus vulgaris L. under normal and drought stress conditions

Purpose: The objective of this study was (a) to investigate the effects of arbuscular mycorrhizal fungi (AMF) and drought stress on Thymus daenensis Celak and Thymus vulgaris L., and (b) to examine the ability of AMF to improve drought stress tolerance in Thymus species. Methods: The experiment was conducted as a factorial pattern in a randomized complete design with three replications in 2017. Factors are four irrigation regimes, consisting of well-watered irrigation after depletion of 20-25% of field capacity (FC), irrigation after depletion of the 35-40% of FC, irrigation after depletion of the 55-60% of FC and two mycorrhizal fungus treatments: non-inoculation with AMF and inoculation with mycorrhiza (F. mosseae, R. intraradices). Results: The results show that drought stress reduces mot and shoot dry weight, relative water content, Photosynthetic pigments, gas change parameters, and nutritional values of two Thymus species, but AMF inoculation increases them. Praline, malondialdehyde, electrolyte leakage, and stomatal resistance increases with increasing water stress, but AMF inoculation ameliorates these increases in corresponding treatments. AMF inoculation increases essential oil production, but water stress in Thymus daenensis decreases it, and in Thymus vulgaris increase, it then decreases it in severe water stress. The results show that root colonization and soil spore density in AMF inoculated treatments increases in low drought stress but decreases with increasing water stress severity. Conclusions: The results suggest that AMF inoculation could be an excellent strategy to alleviate the adverse effects of water stress in two Thymus species cultivation in drought stress conditions.