Effects of Arthrobacter psychrolactophilus B7 on the growth and antioxidant defense system in perennial ryegrass under shade stress

This study aims to investigate the effects of Arthrobacter psychrolactophilus strain B7 on plant growth and the physiological characteristics of the perennial ryegrass under different shade stress treatments (0, 20%, 40%, 60%, and 80%). The combined effects of B7 inoculation and various levels of shade stress on plant growth and physiological characteristics were investigated via pot experiments. The results showed that shade stress significantly inhibited the perennial ryegrass seedling growth (P < 0.05), whereas B7 inoculation alleviated the growth inhibition caused by shade stress. The relative electrolyte leakage and malondialdehyde accumulations increased with increasing shade stress. B7 inoculation significantly reduced the cellular membrane damage and reactive oxygen species (ROS) levels under shade stress (P < 0.05), compared with shade treatment alone. Inoculation of B7 decreased the H₂O₂ and \rmO_2^\rm\cdot - levels by 5.88%, 24.41%, 33.60%, and 40.00%, and by 30.91%, 22.94%, 25.67%, and 49.37% when exposed to 20%, 40%, 60%, and 80% shade stresses, respectively. Additionally, shade stress resulted in an increase in the antioxidant enzyme activities and non-enzyme antioxidant contents, whereas B7 inoculation further improved the activities of superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, glutathione reductase, and the contents of ascorbic acid (AsA) and glutathione (GSH). In conclusion, B7 inoculation could improve the antioxidant defense activities, which led to a decline in ROS, thus enhancing shade tolerance in perennial ryegrass. The present study indicates that A. psychrolactophilus strain B7 has considerable potential for improving the ability of plants to adapt to stress.