Considering the serious pollution of heavy metal-chromium (Cr) in soil, there is an urgent need for effective selection of Cr-tolerant plant species. In order to gain fundamental insights into the tolerance and accumulation capabilities of Lolium perenne L. and Pharibitis purpurea(L.) Voigt under Cr stress, a pot experiment was conducted to investigate their growth, physiology and accumulation characteristics under Cr(Ⅲ) and Cr(Ⅵ) stress. The results showed the growth parameters could intuitively reflect the toxicity levels of Cr for plants. For instance, a low-level Cr(Ⅲ) (<250 mg·kg-1) in soil was good for plant growth as indicated by the significant elevation of plant height, root length and biomass in L. perenne (P<0.05). However, Cr(Ⅵ) at all concentrations (≥25 mg·kg-1) in the soil inhibited the growth of both plant species, and the root length was particularly sensitive to the toxicity of Cr. The physiological parameters of plant represented both the toxicity of Cr and the tolerance of plants under Cr stress. A decrease of root activity and an increase of malonaldehyde content were observed under Cr stress, which indicated the physiological metabolism of plants was disturbed. In the presence of both Cr species, the proline content increased, which served as an indicator for both high Cr toxicity and increase of osmotic balance in plants. A rise in SOD and POD activity reflected the defense ability of plants against oxidative stress caused by Cr. In addition, the Cr-accumulation related parameters were the major standards for tolerant species selection. The Cr(Ⅵ) accumulation capacities of both plant species were greater than their Cr(Ⅲ) accumulation capacities. The maximum accumulation amounts of L. perenne and P. purpurea reached 957.4 mg·kg-1 and 743.3 mg·kg-1 in roots and 394.7 mg·kg-1 and 340.4 mg·kg-1 in shoots, respectively. In comparison with P. purpurea, L. perenne displayed a stronger Cr accumulation capacity in roots with a maximum bioaccumulation factor of 15.55. However, the transport ability of P. purpurea was superior to L. perenne. All of the parameters demonstrated that both L. perenne and P. purpurea could be used as alternative plants for phytoremediation of Cr-contaminated soil.
Keywords: Lolium perenne L.; Pharibitis purpurea(L.) Voigt; accumulation; characterization; chromium; tolerance.