Water use efficiency of three mycorrhizal Lamiaceae species (Lavandula officinalis, Rosmarinus officinalis and Thymus vulgaris)

As a mechanism of plants to adapt to soil water deficits, promotion of water use efficiency has been the focus of strategies to increase crop tolerance to drought. Probable improvement of arbuscular mycorrhizal fungi (Funnelliformis mosseae or Rhizophagus irregularis) for the essential oil and biological yield of watered and rainfed host plants (lavender, rosemary and thyme) are the main aim of this study. Physiological responses of the host plants to inoculation with two species of fungi were evaluated under different irrigation regimes (irrigation at 75 and 50% of field capacity, and rainfed). A factorial (two factors) experiment was conducted for two years (2015-2016) based on a randomized complete block design with three replications at Urmia University. Inoculation with these root symbionts increased the colonization of the plants as compared to non-inoculated plants. The seedlings inoculated with fungi and subjected to water stress had more successful colonization. Stress reduced biological yield of inoculated and non- inoculated plants. Drought-induced reduction of biomass was significantly compensated for by mycorrhizal fungi. The highest essential oil percentage was obtained in rainfed condition. Since water use efficiency is affected by economic performance and volume of used water in different years, the results were variable. Increasing irrigation intervals can help the plants to adapt to water stress and prevent significant reduction in water use efficiency. However, in general, this study showed that inoculation with fungi is effective in alleviating adverse effects of water stress.