Influence of Arbuscular Mycorrhizal Fungi on Morphophysiological Responses and Secondary Metabolism in Lippia alba (Verbenaceae) Under Different Water Regimes

In this study, we evaluated the influence of arbuscular mycorrhizal fungi (AMF) on the morphophysiological responses and production and composition dynamics of essential oils (EOs) in Lippia alba plants subjected to different water treatments. Cuttings of L. alba were planted in sterile soils either with or without AMF spores. Sixty days after planting, the plants were subjected to two water regimes: hydrated (75%) and water deficit (WD, 25%) for 60 days. Growth evaluations, gas exchanges, biochemical and morphophysiological analyses, and content and composition of the EOs were carried out. WD reduced the production of root biomass, stomatal density, water use efficiency, root/leaf biomass ratio, specific leaf area, leaf phosphorus content, and levels of photosynthetic pigments. It increased leaf temperature, antioxidant enzyme activity, and osmolyte accumulation in leaves and roots. In contrast, the association of AMF in plants under the WD regime promoted an increase in root biomass, specific leaf area, leaf relative water content, levels of photosynthetic pigments, leaf accumulation of carbohydrates, and content of EOs. WD and mycorrhization influenced the production of EO compounds, favoring the production of sesquiterpenes over the reduction of monoterpenes. The results showed that the beneficial action of AMF was greater when plants were under WD than when hydrated. Thus, WD promotes morphophysiological changes in L. alba. However, mycorrhization increases the tolerance, production, and composition of EOs in plants under water restriction. Therefore, AMF can be considered bioprotective in plants under water restriction and an enhancer of EO production. [GRAPHICS] .