Arbuscular mycorrhizal fungi improve drought tolerance of tea plants via modulating root architecture and hormones

The tea plant [Camellia sinensis (L.) O. Kuntze] is an evergreen crop with a shallow root system that predominantly grows in acidic soil, strongly dependent on arbuscular mycorrhizal fungi. The present study evaluated the effects of a proven effective arbuscular mycorrhizal fungus (AMF), Claroideoglomus etunicatum, on plant growth performance, root morphology, root hair variables, root endogenous hormones, and root nutrient contents of Camellia sinensis cv. 'Fuding Dabaicha' seedlings under well-watered (WW) and drought stress (DS) conditions. After 8 weeks of DS treatment, root AMF colonization was decreased by 58.77%. AMF inoculation significantly increased plant height, leaf biomass, and root biomass, irrespective of soil moisture status. Mycorrhizal fungal colonization also significantly increased root volume, number of lateral roots, length of lateral roots in different classes, and root hair variables (e.g., density, length, and diameter) under both WW and DS conditions. AMF-colonized roots had higher concentrations of abscisic acid, brassinosteroids, gibberelins, and indole-3-acetic acid, which were significantly correlated with changes in root morphological parameters. AMF-inoculated plants represented higher root P, K, Ca, Mg, Fe, Mn, and Zn concentrations as compared with non-AMF-inoculated plants, regardless of the soil moisture status. These results concluded that arbuscular mycorrhizal plants under DS had superior adaptability of root morphology to promote nutrient acquisition, which was associated with higher hormone levels in roots induced by AMF.