Study on the soluble salt ions contents of Populus alba L.var.pyramidalis growing in salinity soils POLLEN CHROMOSOME DOUBLING UNDER HIGH TEMPERATURE IN Populus alba L. Colchicine-induced Pollen Chromosome Doubling and its Cytological Effects in Populus alba L. Isolation and Purification of Mesophyll Protoplasts of Populus alba L. var. pyramidalis Sap flow dynamics of Populus alba L.×P.talassica plantation in arid desert area