Investigating the effect of arbuscular mycorrhizal fungus on the growth, osmotic adjustment and phosphorus uptake of valerian (Valeriana officinalis L.) under drought stress conditions

The Valerian plant (Valeriana officinalis L.) is one of the most important medicinal plants known in the world and native to Europe and Asia, which has been considered and used by humans in traditional medicine since ancient times. In this study, in order to evaluate the effect of inoculation with Funneliformis mosseae and drought stress on some characteristics, including growth parameters, osmotic adjustment and phosphorus uptake of valerian plant, a factorial experiment was conducted in a completely randomized design with 4 replications for two months. The experimental factors included two fungi levels (non-inoculated (control) and inoculated) and three levels of drought stress (90-100% (control), 60-70%, and 40-50% of field capacity (FC)). The results showed that drought stress significantly reduced the biomass, leaf relative water content, and phosphorus concentration of shoot and root at both 60-70% FC and 40-50% FC levels, and the chlorophyll content at 40-50% FC level. In this research, growth parameters, chlorophyll content and phosphorus concentration increased due to colonization with F. mosseae at both stress levels. Biochemical analyses also showed that the contents of soluble sugars, protein and malondialdehyde (MDA) in the shoots and roots of valerian significantly increased under drought stress. Mycorrhizal inoculation of valerian caused an increase in shoot protein at 60-70% FC level and conversely, it caused a decrease in the contents of soluble sugars and MDA in shoot and root and protein of root at both 60-70% FC and 40-50% FC levels compared to non-inoculated plants. In general, the colonization of valerian plants with F. mosseae by modulating the effect of drought stress could be a suitable and efficient method to mitigate the detrimental effects of drought stress on the symbiotic plants.