Effects of mycorrhizal fungi on plant growth, nutrient absorption and phytohormones levels in tea under shading condition

Abstract

High temperature and strong light could induce bitterness and astringency of tea (Camellia sinensis (L.) O. Kuntze) in summer. Arbuscular mycorrhizal (AM) fungus and shading could change tea growth surroundings and improve its quality. The present study evaluated the inoculated effects of an arbuscular mycorrhizal fungus (AMF), Glomus etunicatum, on plant growth, root morphology, leaf nutrient status, phytohormones and the relative expression of root CsCPC, CsTTG1, CsAUX1, CsYUCCA1, CsNCED2, CsGA3OX1, CsDWF4 and CsAOS genes in Camellia sinensis  ‘Xinyang population’ seedlings in sands under shading conditions. After 14 weeks of AMF inoculation, root mycorrhizal colonization ranged from 18.5% to 48.00%. AMF inoculation and shading heavily increased plant height, shoot and root biomass, total root length and volume, leaf nutrients content (except Fe), respectively. Both mycorrhizal inoculation and shading significantly increased root hair growth respectively, in company with up-regulation gene CsCPC and down-regulation gene CsTTG1. Root auxin level and its transport gene CsAUX1 was both up-regulated by mycorrhizal inoculation and shading. Interestingly, auxin biosynthesis gene CsYUCCA1 has not been affected, which suggested that both mycorrhizal and shading mainly regulate auxin transport but not biosynthesis pathway. The contents of gibberellin (GA) and brassinosteroid (BR) in root were notably increased by mycorrhizal inoculation and shading, accompanied with up-regulation of its biosynthesis genes, CsGA3OX1 and CsDWF4. With regard to the growth inhibiting phytohormones abscisic acid (ABA) and jasmonic acid (JA), mycorrhizal inoculation and shading significantly decreased their levels in root, in company with down-regulation of biosynthesis genes, CsNCED2 and CsAOS. These results implied that both AMF inoculation and shading could enhance the tea plant stress resistance and increase nutrient absorption, root biomass and the contents of root phytohormones by up-regulating its transport and biosynthesis pathway.