Impacts of the Inoculation of Piriformospora indica on Photosynthesis, Osmoregulatory Substances, and Antioxidant Enzymes of Alfalfa Seedlings under Cadmium Stress

Abstract

With the random discharging of industrial and agricultural wastewater, a large amount of cadmium (Cd) has accumulated in the soil, which seriously affects the growth of crops and people’s food safety. In this study, alfalfa was used as the material for studying the effects of the inoculation of Piriformospora indica (P. indica) on photosynthesis, osmoregulatory substances, and antioxidant enzymes of alfalfa seedlings at different Cd concentrations (0, 5, 10, 30, 50, and 100 mg/L) through hydroponic experiments. The results showed that with the increase in Cd concentration, the chlorophyll content, net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) of alfalfa all decreased gradually, while the intercellular CO2 concentration (Ci) decreased at first and then increased. However, compared with non-inoculated control plants, the inoculation of P. indica improved the photosynthesis (41.97%) of alfalfa under Cd stress, increased the chlorophyll content (43.70%), and significantly increased the contents of proline (29.86%), soluble proteins (38.54%), and antioxidant enzyme activities. It was concluded that P. indica alleviates the negative effects of Cd on alfalfa plants to some extent. This is because P. indica can resist Cd stress and improve plant growth in cadmium-contaminated agricultural soil by alleviating membrane peroxidation damage, regulating osmotic regulatory substances, and enhancing enzyme activity to improve the antioxidant defense system. Thus, P. indica can be considered a biological fertilizer for improving plant growth and physiology in soils contaminated with cadmium.