Abstract: The spatial,temporal,quantitative and chemical patterns of nitrogen nutrition of larch(Larix olgensis)and ash (Fraxinus mandshurica)trees were studied in a belt-mixed (12-year-old) plantation,along with an additional pot experiment on larch and ash seedlings.That the two forest species had very different nitrogen-nutrition patterns in all the aspects mentioned above.In the shared below-ground space of mixed stand,the active fine roots of ash trees adjacent to larch belt dominantly occupied the uppermost layer of soil(0～20cm),while larch fine roots were pressed to deeper soil layers(20～60cm)by the exclusive competition from ash.In the whole growing season from May to September,both species showed evident peak period of N absorption.The peak period of ash trees appeared in middle-late June,while that of larch trees came up in middle-late July,approximately one month later than ash.In the quantitative aspect,ash consumed relatively larger amount of N with a lower nitrogen-use efficiency(NUE),while larch only required relatively smaller amount with a higher NUE(60.8% higher than ash).As for the apparent preferences for different inorganic forms of nitrogen nutrient(NH₄⁺ or NO₃^-),ash tended to select NO₃^- as its favourite nitrogen source,while larch seemed to be neither NO₃^- nor NH₄⁺ preferred.