Isotopic Specificity of Representatives of the Family Gentianaceae in High Mountains of the Holarctic

Partial mycoheterotrophy (mixotrophy, obtaining organic substances from mycorrhizal fungi) is widespread in mycorrhizal flowering plants. We hypothesized that alpine members of the Gentianaceae family, which contain fully mycoheterotrophic species with arbuscular mycorrhiza, may be largely mixotrophic. The isotopic (δ13С, δ15N, δ2H, and δ18O) and elemental (C and N) composition of leaves and roots of 13 pairs of high-mountain plant species (Gentianaceae species and nearby reference plants – dicotyledons with arbuscular mycorrhiza) of three Holarctic Mountain systems (Alps, Caucasus, and Tibet) were studied. Contrary to our hypothesis, the organic matter of the leaves and roots of Gentianaceae was not enriched in deuterium (2H) compared to reference plants, indicating the absence or low significance of mycoheterotrophy in the studied species. Leaves and roots of gentian plants had higher values of δ15N and δ18O, but lower values of δ13C and δ2H compared to the leaves and roots of reference plants. The leaves and roots of gentian plants contained more C, but the N content in the leaves was higher and, in the roots, it was lower than in the corresponding organs of the reference plants. We hypothesized that these results could be explained by more intense nitrogen fixation by prokaryotes of the leaf microbiome, providing better nitrogen nutrition to leaves and their more intense photosynthesis and transpiration.