Stable nitrogen isotope ratio in wood substrates and xylotrophic fungi in forest ecosystems of Western Siberia

It has been shown that wood substrates are the main source of nitrogen for xylotrophic fungi, which have almost the same isotopic signature as their substrate. This fact and a strong positive correlation in nitrogen isotope composition between the substrates and fungi provide evidence for a closed type of nitrogen turnover in the wood-fungus system that is based on retention and repeated utilization of this element. Its isotope composition in the fungi depends on that in the substrate, which is enriched in the heavy isotope in deciduous wood and in the light isotope in coniferous wood. The nitrogen isotope composition in the fungi and wood substrates does not depend on the degree of wood mineralization or climatic conditions, and δ¹⁵N is not an indicator of fungal physiological activity or wood decomposition rate but rather a marker of the isotopic composition of nitrogen sources for the fungi.