Arbuscular mycorrhizal fungi improve nutrient status of Commiphora myrrha seedlings under drought

In dryland ecosystems, tree and shrub seedling establishment, growth and survival are limited by access to water and nutrients. Arbuscular mycorrhizal fungi (AMF) increase seedling establishment and survival by enhancing nutrient and water acquisition. We executed a fully-factorial greenhouse experiment to determine the interactive effect of AMF (with and without), water deficit (four levels), and soil layer (topsoil and subsoil) on the biomass, growth, nutrient concentrations, and mycorrhizal root colonization of seedlings of Commiphora myrrha, a tree species that dominates large areas of dry forest and woodland in the Horn of Africa. Mycorrhizal seedlings had higher root and shoot biomass than non-mycorrhizal seedlings. They also had higher nutrient concentrations in root and shoot. Plant biomass was higher when plants were grown in topsoil at lower soil moisture levels. Mycorrhizal responsiveness was highest at lower soil moisture. The drought response index was higher for mycorrhizal than for non-mycorrhizal plants, indicating enhanced mycorrhizal benefits at lower water supply. Seedlings grew better in topsoil than in subsoil. Mycorrhizal colonization of roots of C. myrrha seedlings was higher with lower moisture and higher in topsoil than in subsoil. The increased performance of mycorrhizal C. myrrha indicates that mycorrhization is a major component of the adaptive strategy of seedlings of this species, similar to other species in these dryland deciduous ecosystems. We conclude that for restoration purposes with this species, nursery seedlings should be mycorrhized because of their enhanced growth performance.