The relative low content of bound water,soluble sugar, K + , Carotenoid and ABA in the leaf tissue of P. ponderosa was the internal cause of its weak cold resistance.

• 美国黄松针叶组织中束缚水、可溶性糖、K+、类胡萝卜素和ABA含量较低是其抗寒性弱的内在原因。