The experiment used three poplar varieties(P,psuedo-simonii×P.nigra×P.nigra C L.'A5', P.psuedo-simonii×P.nigra×P.nigra C L.'HeilinⅢ',P.deltoides×P.cathangana) with different frozen resistance as tesing materials.The membrane permeability,phenols content, polyphenoloxidase activity and soluble sugar content response to the temperature strikingly dropped in different frozen resistance poplar leaves which treated with low temperature when poplar won't enter into dormancy phase in autumn.The results was...