Effects of single and combined stresses of lead, zinc and cadmium on growth and physiological characteristics of perennial ryegrass

【Objective】To explore the effects of single and combined pollution of lead(Pb), zinc(Zn), cadmium(Cd) on the growth and physiological characteristics of perennial ryegrass, and to improve the scientific basis for testing the resistance ability of perennial ryegrass to soil heavy metal pollution.【Method】Used sand culture method, the effects of single and combined stress of CK(no heavy metal), Pb, Zn and Cd on plant height, leaf width, root length, biomass, chlorophyll content, proline(Pro), peroxidase(POD), superoxide dismutase(SOD), soluble sugar(SS) and malondialdehyde(MDA) of perennial ryegrass were studied by pot experiment, and growth and physiological characteristics indexes were comprehensively evaluated by subordinate function method.【Result】Pb-Zn-Cd treatment had the greatest effect on plant height, leaf width, root length, tiller number, aboveground biomass, underground biomass, root-shoot ratio, POD activity and SOD activity of perennial ryegrass, plant height, leaf width, root length, tiller number, above ground biomass, underground biomass, root-shoot ratio decreased by 61.9%, 35.9%, 66.5%, 72.1%, 92.8%, 94.2% and 20.1% compared to CK, respectively. POD activity and SOD activity increased by 64.6% and 3.8 times compared with CK. Compared with CK treatment, Zn treatment had the greatest effect on chlorophyll a content, carotenoids content, total chlorophyll content and total photosynthetic pigment content, and they significantly decreased by 28.6%, 31.9%, 20.6% and 22.9% compared with CK(P<0.05, the same below). Cd treatment had the largest inhibition effect on chlorophyll b content, followed by Pb-Zn-Cd treatment, and they were decreased by 20.3% and 20.0% compared with CK. All heavy metal treatments resulted in significant increase in Pro content in perennial ryegrass. The contents of SS and MDA were most affected by Zn-Cd treatment, increased by 56.4% and 7.0 times compared with CK. The effects of combined stress on the indexes of perennial ryegrass were interactive. According to the comprehensive evaluation of membership function, the tolerance of perennial ryegrass was Zn> CK> Cd> Zn-Cd> Pb-Zn> Pb> Pb-Cd> Pb-Zn-Cd.【Conclusion】Perennial ryegrass has some tolerance to Zn stress, but it has the worst tolerance to Pb-Zn-Cd compound stress.