The ratio of stable isotopes of nitrogen (15N and 14N) has been assessed in leaves of the forest plants from different functional groups (with ectomycorrhiza, ericoid, and arbuscular mycorrhiza; in a nitrogen-fixing symbiosis) under the conditions of strong transformation of ecosystems by the Karabashsky Copper-Smelting Plant effluents in the Southern Urals. The abundance of 15N in the plants generally increases in polluted habitats. The abundance of the heavy isotope 15N increases significantly with pollution in ericaceous dwarf shrubs (by 3.3‰) and herbs with arbuscular mycorrhizae (by 2.8‰). This indicates a strong alteration in conditions or modes of plant mineral nutrition under the influence of heavy metal pollution of forest ecosystems.