Cold Tolerance Variation of Populus cathayana Clones from Different Populations

This article expounded the cold tolerance of 21 populations of Populus cathayana clones,which was measured by conductimetry method. The samples collected for the experiment were one-year-old dormant shoots of three-year-old trees which came from 17 individuals of each populations. Differences were found among individuals within the same populations,but the differences among populations were significant. Cold tolerance among populations correlated with latitude positively. The dormant time and budbreak time were also investigated and it showed that the dormant time and budbreak time correlated positively with latitude,which demonstrated that the early frost tolerance in late autumn,cold tolerance in winter and late frost tolerance in early spring of each populations were the result of adapting the ecological factors of origin places.