Abstract: A pot experiment with white clover (Trifolium repens) and red clover (T. pratense) was conducted to study their growth and physiological indices under the stress of freezing-thawing cycle, aimed to understand the effects of future climate change on the growth of clover. After the stress, white clover survived, while red clover dead. The leaf membrane permeability, MDA content, antioxidant enzymes activity, and osmoregulation substances contents of the two clovers increased in thawing-freezing phase but decreased in freezing-thaw phase. During thawing-freezing and freezing-thawing, the leaf POD and CAT activities of cold-resistant white clover were higher than those of coldsensitive red clover, the white cover’s leaf proline content was 5 times higher than red clover’s, and the leaf membrane permeability of white clover was lower than that of red clover. All the physiological indices of white clover peaked at -5 ℃ while those of red clover peaked at -10 ℃, suggesting that -5 ℃ would be a temperature point at which the physiological regulation reaction occurred to make white clover’s leaf cell adapt to ice formation and ice melting, and maintain the balance between oxygen free radicals production and scavenging. Our results suggested that white clover had higher capability to adapt to freezing-thawing cycle, and could be a good landscaping species in future application and popularization.

Key words: dicyandiamide, 3,5-dimethylpyrazole, hydroquinone, nitrogen transformation, apparent nitrification rate, nitrification inhibition rate.