Growth status of Lolium perenne and Medicago sativa and their manganese absorption in manganese residue-soil mixed matrixes

Using Medicago sativa and Lolium perenne as the experimental materials, the growth status of M. sativa and L. perenne and their absorption characteristics of manganese in electrolytic manganese residue-soil mixed matrixes were examined in this study. The germination rate of M. sativa and L. perenne decreased after mixing variable proportions (7%, 14%, 21%, 28%, and 35%) of electrolytic manganese residue (EMR) in the soil, whereas the biomass first increased and then decreased with an increase in the amount of EMR. The height of the two plants increased to different degrees, especially for L. perenne. With an increase in EMR, the photosynthetic pigment content in L. perenne was increased. In the 14% EMR treatment, the chlorophyll content was the highest, significantly higher than the control by 34.7% (P < 0.05). The chlorophyll and carotenoid content in M. sativa first increased and then decreased with the addition of EMR. In the 14% EMR treatment, the chlorophyll and carotenoid content increased significantly, 59.7% and 28.0% higher than the control, respectively. After adding EMR to the soil, the malonaldehyde (MDA) content and activity of the antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) in M. sativa increased significantly, whereas the MDA content and activity of SOD, CAT, and POD in L. perenne did not change, indicating that the tolerance of ryegrass > alfalfa. The manganese content in the aerial parts and roots of M. sativa and L. perenne increased with an increase in EMR. The enrichment coefficient of manganese was L. perenne > M. sativa, and the transfer ability of manganese was M. sativa > L. perenne. Both plants could be used as candidate plants for the ecological restoration of manganese residue; however, the inhibitory effect of manganese residue on M. sativa was greater than that of L. perenne. Therefore, L. perenne was more suitable as a pioneer plant for the ecological restoration of manganese residue.