By sand culture in greenhouse, the experiment of growing process on four exotic alders including Alnus glutinos, Alnus rubra, Alnus nitada and Alnus incana were conducted under four different concentrations of nitrogen (N0, N1/2, N1, N2) in order to discover the growing responses to nitrogen and to analyze root morphology of seedling, accumulation and utilization efficiency of nitrogen. The results showed that the growth parameters of 4 exotic alders, such as the total biomass, accumulation of nitrogen, length of root, surface area of root, volume of root and number of rootlets increased when the concentration of nitrogen varied from no nitrogen (N0) to low nitrogen (N1/2), yet decreased at normal nitrogen (N1) and high nitrogen (N2). However the rootlet ratio and utilization efficiency of nitrogen decreased significantly with increasing nitrogen supplied. Among 4 experimental materials, Alnus glutinos and Alnus rubra had higher total biomass, accumulation of nitrogen, root morphological parameters and nitrogen utilization efficiency than Alnus nitada and Alnus incana, and they could be potentially used in ecological protection and plantations for short rotation trees in the plain of middle and lower Yangtze River. Although the alders had certain nitrogen fixation ability, certain amount of nitrogen fertilization is still needed in the low fertility sandy soil and hilly region in the intensive management of plantations of alders.