Abstract: Under environmental stresses,trees often change their morphological and physiological components to acquire the most limited resources.In northeastern forest region of China,the decomposition and mineralization of litters occur slowly due to low temperature,which often results in forest trees suffering from nutritional stress.With pot culture in greenhouse,this paper studied the effects of nitrogen stress on the physiological and morphological components of Fraxinus mandshurica seedlings.The results showed that under N stress,the net uptake rate of nitrogen and phosphate by the seedlings decreased,while their nitrogen and phosphate use efficiency were higher than those of the seedlings supplied with 8 mmol稬^-1 or 16 mmol稬^-1 of nitrogen during the early growth stage.When suffering from N stress,the leaf mass ratio of the seedlings reduced,with specific leaf area and root mass ratio increased.The relative growth rate increased with the increasing N concentrations supplied to the seedlings during the whole growth period.Under N stress,the net assimilation rate decreased,which resulted in the decrease of total biomass,and the root/shoot ratio was significantly higher than that of the seedlings supplied with 8 mmol稬^-1 or 16 mmol稬^-1 of nitrogen during the early growth stage.There was no significant difference during the late growth stage.

Key words: Nitrogen stress, Nutrient uptake, Biomass distribution, Fraxinus mandshurica