The 2-year-old Yucca brevifolia seedlings were processed by using different ways of low temperature overwintering test,their degree of freezing injury and physiological and biochemical indexes were determined.The results show that as the severity of freeze injury,the content of the membrane permeability and the free proline and the soluble sugar gradually increased,the content of chlorophyll gradually decreased.The severity of freeze injury of soil covering container seedlings is the most serious,the conten...