Emission of Volatile Metabolites by Introduced Juniperus L. Species under Winter Cold Stress: Putative Protective Role and Ecological–Hygienic Assessment

The profile of volatile organic compounds (VOCs) in the equilibrium headspace of intact shoots of four juniper taxa (Juniperus communis, J. scopulorum, J. sabina, J. media ‘Mint Julep’) was studied during winter physiological dormancy (December) under introduction conditions (Moscow). The analysis was performed by static headspace gas chromatography–mass spectrometry (HS-GC-MS) at 40°C, which provides a physiologically relevant model of the natural insolation of dark-coniferous shoots in winter. An absolute predominance of monoterpenes and a strict species specificity of native emission were revealed. A pronounced α-pinene chemotype (86.1%) was established for J. communis; a sabinene chemotype for J. scopulorum and J. sabina (69.9 and 53.2%, respectively); and a complex limonene–sabinene chemotype for J. media ‘Mint Julep’ (D-limonene 34.1%). The inhalation toxicity of J. sabina in winter under an urban ecosystem was shown to be minimal owing to physicochemical constraints: the low vapor pressure of the toxic sabinyl acetate reduces its share in the emission to trace values (0.4%). The intense emission of D-limonene and α-pinene by the other species is considered in the context of hidden risks: autoxidation of these monoterpenes in a polluted urban atmosphere leads to the formation of secondary hydroperoxides with a pronounced allergenic and sensitizing potential.