Abstract: Studies on the spatial, temporal, quantitative, and form aspects of nitrogen uptake by Pinus koraiensis and Betula platyphylla showed that in pine-birch mixed forest, birch tree was characterized by typical shallow-roots, and its nutrient-seeking roots were largely distributed in topsoil; while pine tree was characterized by deep roots, and its nutrient seeking roots were obviously increased in deep soil. As for seasonal dynamics of Nuptake, birch showed an intensive uptake with a remarkable peak period, while pine shadowed by birch performed gently in the whole growing season without any significant peak period. In the quantitative aspect, birch consumed relatively larger amount of N, while pine only required relatively smaller amount of it and the Nuse efficiency was 34% higher than that of birch. As for the selective uptake of chemical Nforms, birch tended to select NO₃^--N, while pine preferred to NH₄⁺-N.

Key words: Pinus koraiensis, Betula platyphylla, Nitrogen nutrition, Behavior, solar greenhouse, soil evaporation, crop coefficient, crop transpiration, water stress coefficient