Abstract: In this study, the activities of superoxide dismutase (SOD), peroxide (POD) and catalse (CAT), and the contents of soluble sugar, soluble protein, proline, malondialdehyde and chlorophyll in different aged leaves (young, middleaged, old) of white clover (Trifolium repens) were investigated in different seasons to understand how different aged leaves of white clover adapt to different seasonal temperatures in physiology and what ecological role of leaf senescence plays in maintaining stolon growth. The result showed that: (1) young leaves grown in winter had lower MDA content, and higher values in chlorophyll a content, SOD and POD activities, and soluble sugar and proline contents. However, young leaves grown in summer had higher MDA and chlorophyll b contents, but had lower SOD and POD activities and soluble sugar and proline contents. It is indicated that young leaves had higher physiological regulation plasticity in adaptation to different seasonal temperatures. (2) There existed a similar model of physiological regulation in the developing leaves grown in different seasons. When young leaves became mature, the contents of chlorophyll and soluble sugar and proline, and the activities of SOD and POD increased, while MDA content decreased. (3) Aging leaves grown in different seasons had same physiological characteristics. With the leaves becoming senescent, the soluble sugar and proline contents still increased, but the activities of SOD and CAT and content of MDA decreased. The antioxidant enzyme system and osmoregulation played an important role in physiological protection of young leaves to adapt different seasonal temperatures and in keeping their rapid growth by maintaining metabolic balance of oxygen free radicals and water metabolic balance. During leaf development, the antioxidant capacity decreased, and the proline and soluble sugar kept on accumulation, which was the reason inducing leaf senescence and short life. However, short life of leaves grown in different seasons would make more energy and matter being allocated to stolon top and promote leaf initiation, stolon elongation growth, and population expansion, which played an important physiological regulating role in maintaining growth of white clover in different seasons.

Key words: climatic mean value, rice, delayed growth-type cold damage, evaluation, Liaoning Province.