| Summary: | δ<sup>13</sup>C and δ<sup>15</sup>N were analyzed in the leaves of <i>Pinus sylvestris</i> L. and <i>Betula</i> spp. under the conditions of severe heavy metal (Zn, Cu, Cd, and Pb) contamination. Twenty-seven plots located near the Karabash copper smelter (Russia) were studied. No reliable correlation of <sup>13</sup>C in tree leaves with the level of pollution was observed. δ<sup>15</sup>N, both in <i>Pinus sylvestris</i> and <i>Betula</i> spp., increased similarly in polluted areas. δ<sup>15</sup>N was increased by 2.3‰ in the needles of <i>Pinus sylvestris</i> and by 1.6‰ in the leaves of <i>Betula</i> spp. in polluted plots compared to the background ones. The probable reasons for the increase in δ<sup>15</sup>N were estimated using multiple regression. The regression model, which includes two predictors: δ<sup>15</sup>N in the humus horizon and the occurrence of roots in the litter, explains 33% of the total variability of δ<sup>15</sup>N in leaves. Thus, in ecosystems polluted with heavy metals, the state of trees is determined not only by the direct toxic effects of heavy metals but also by indirect ones associated with the features of plant mineral nutrition. This fact opens the way to the search for opportunities to control the state of plants in disturbed ecosystems by regulating the content of mineral nutrition elements.
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