Arbuscular mycorrhizal fungi improve plant growth of Ricinus communis by altering photosynthetic properties and increasing pigments under drought and salt stress

Castor bean (Ricinus communis) is one of the most important candidate crops that can be used to increase the land cover and crop yield in the arid and saline region of China. To evaluate the effects of arbuscular mycorrhizal (AM) fungi on the growth of castor bean under drought and salt stresses, a pot experiment was carried out to examine how AM fungi improve the plant growth of castor bean by affecting the leaf gas exchange, pigments, and metabolites accumulation of castor bean seedlings. The results showed that AM fungi stimulated plant growth and increased the castor bean aboveground biomass. AM fungi significantly increased the net photosynthetic rate (A), stomatal conductance (g(s)) and transpiration rate (E) of castor bean and decreased the intercellular CO2 concentration (Ci) under drought and salt stress. The contents of chlorophyll a, chlorophyll b, chlorophyll a + b and carotenoids in leaves treated by AM fungi were higher than in those without the AM fungi treatment. AM fungi notably increased the soluble protein and proline contents and decreased the malondialdehyde (MDA) content of castor bean. The results indicated that AM fungi could protect castor bean against drought and salt stresses by improving its leaf gas exchanges and photosynthetic capacity and altering its concentrations of metabolites. Our results highlight that AM fungi might be a promising bio-approach that can be used to plant castor beans in northeast and northwest China.