The dynamic changes of cold tolerance in different vegetative organs ofthree warm season turf grasses during the overwintering

From October 2008 to May 2009, changes of electrolyte leakage rate in leaves, stems and rhizomes of three warm season turf grasses (Zoysia japonica Lanyin No.3, Cynodon dactylon Yangjiang and Eremochloa ophiuroides E126), which in simulated cold treatment were determined with improved conductivity method, and the freezing lethal temperature of 50%(LT50) was estimated by the means of fitting Logistic equation, as well as the seasonal dynamic changes and differences of cold tolerance among different organs were analyzed, comparatively. The results indicated that LT50 in leaves, stem and rhizomes of three warm season turf grasses showed decreased firstly then increased sharply with seasonal changes in field temperature which was dropped in overwintering and increased in spring. The rhizomes of Z. japonica Lanyin No.3, the rhizomes of C. dactylon Yangjiang and stems of E. ophiuroides E126 showed better cold tolerance .In summary, Z. japonica Lanyin No.3 had the greatest cold tolerance, E. ophiuroides E126 was second, and C. dactylon Yangjiang had poor cold tolerance by analyzing the dynamic seasonal changes of LT50 and observing the phenophase in field.