Contributions of an arbuscular mycorrhizal fungus to growth and physiology of loquat (Eriobotrya japonica) plants subjected to drought stress

Loquat (Eriobotrya japonica) is an evergreen tree with a shallow root system subjected to drought stress. We have found that AM fungi can alleviate drought stress by improving loquat nutrient uptake. However, the physiological mechanisms of improving drought tolerance have not been described so far in loquat mycorrhiza symbiosis. Funneliformis mosseae was used as arbuscular mycorrhizal fungus and loquat was selected as a model for an evergreen, woody plant. Thus, a pot experiment with four treatments was conducted. Growth, leaf water status, solute accumulation, oxidative damage to lipids, antioxidant activities, and phytohormones were evaluated by non-mycorrhizal (NM) and arbuscular mycorrhizal (AM) loquat plants growing under well-watered or drought-stressed conditions. Results showed that AM plants had higher dry-biomass production and leaf water potential than NM plants under drought-stressed conditions. The drought-stressed AM roots accumulated more proline than in NM roots, while not in leaves. Lipid peroxides of leaves and roots in drought-stressed AM plants were 26 and 61 % lower than in NM plants. The AM symbiosis may enhance osmotic adjustment in roots, contributing to maintaining a water potential gradient and water absorption from soil into the roots. The cumulative effects increased the AM plant tolerance to drought stress. The results are compared to findings reported hitherto mainly from short-lived, herbaceous AM plants in the literature.