The ground-cover chrysanthemum （Dendranthemaxgrandiflorum Kitamura） ＇Zixunzhang＇ was used as the experimental material in this study. The physiological and biochemical indexes of leaves, emergent rhizomes and roots from ＇Zixunzhang＇ growing in the open field during the autumn and winter in Beijing area were deter- mined. These indexes showed that root activities decreased slowly with the drop in temperature. The relative water contents of leaves and emergent rhizomes, and the water content of roots decreased. The activities of SOD, CAT and POD from leaves and emergent rhizomes were affected significantly by low temperature, but their change trends were different, which suggested that these 3 enzymes might play an interacted role in the formation of the cold tolerance of ＇Zixunzhang＇ mum, while the changes of the three enzyme activities in roots were little when the tem- perature dropped. With the significant increasing of the content of soluble sugar from leaves, the contents of soluble protein and proline declined overall; and the contents of osmotic regulation substances of emergent rhizomes and roots increased at first and then decreased. The correlation analysis indicated that the cold toler- ance of ground-cover mum ＇Zixunzhang＇ was related closely to relative water con- tents, SOD enzyme activity, soluble protein, soluble sugar and root activity. The morphological observation of leaves, emergent rhizomes and roots also showed that the survival of the ground-cover mum mainly depended on the cold tolerance of roots during the overwintering.
