『Abstract
　Uptake of nitrogen (N) via root-mycorrhizal associations accounts for a significant portion of total N supply to many vascular plants. Using stable isotope ratios (δ¹⁵N) and the mass balance among N pools of plants, fungal tissues, and soils, a number of efforts have been made in recent years to quantify the flux of N from mycorrhizal fungi to host plants. Current estimates of this flux for arctic tundra ecosystems rely on the untested assumption that the δ¹⁵N of labile organic N taken up by the fungi is approximately the same as the δ¹⁵N of bulk soil. We report have hydrolysable amino acids are more depleted in ¹⁵N relative to hydrolysable ammonium and amino sugars in arctic tundra soils near Toolik Lake, Alaska, USA. We demonstrate, using a case study, that recognizing the depletion in ¹⁵N for hydrolysable amino acids (δ¹⁵N = -5.6‰ on average) would alter recent estimates of N flux between mycorrhizal fungi and host plants in an arctic tundra ecosystem.

Keywords: ¹⁵N; Arctic tundra; Decomposition; Hydrolysable amino acids; Mycorrhizal fungi; Nitrogen transfer; Plant-fungal interaction』

Abbreviations
Introduction
Methods
Results and discussion
　δ¹⁵N of soil and plant N
　Pathways of N in arctic tundra ecosystems
　Implications
Acknowledgements
References