The Accumulation of Poisonous Elements in Populus×euramericana,Salix matsudana,Ulmus pumila and Robinia pseudoacacia Growing on Coal Ash“Soil”

The speciai"soil"type condition is formed by filling the collapsed area with coal ash from thermal power factory and covering 30cm Chao soil onto the ash.In 1986～1987,Populus×euramericana,Salix matsudana,Ulmus pumila and Robinia pseudoacacia plantations were established on the site.Under intensive cultivation,they grew well.Biomass and 14 elements distribution and accmulation,in the trees were investigated in 1991.The result shows that most elements such as N,P,K,Ca,Mg were accumulated mainly in leaf,then root,bark and branch,their contents in trunk the least.Among the 4 species,Robinia pseudoacacia had the highest N content.The accumulation of the poisonous elements in tree was Hg mainly in root and bark,seldom in leaf and branch;Pb mainly in leaf and bark,seldom in trunk;Cd and Cr distributed evenly in all organs.The absorption of nutritive and poisonous elements was calculated by their 4～5 years biomass and element contents.The trees purification function was discussed based on the calculation.