The mechanisms of biological invasion were clarified through nitrogen (N) dynamics on a succession starting on N-poor Koma volcano, Hokkaido, Japan, by evaluating differences in mycorrhizal N-transfer between native and biologically-invasive plants, and effects of invasion on litter accumulation, N-deposition in the substrates and solar radiation.  N status of invasive Larix kaempferi (larch), native trees, shrubs, sedge, mycorrhizal fungi and tephra was evaluated with elevations. Mycorrhizal N-transfer was evaluated by stable N isotope ratios.  The N dynamics was examined with changes in vegetation, litter and solar radiation.  The dominant pioneer shrub, Salix reinii (willow), increased total N in the substrates on low-vegetated elevations.  Larch changed N dependence on mycorrhizal fungi flexibly depending on N in the tephra, while native trees showed high mycorrhizal dependence independent of N in the tephra.  The abundance of larch caused thick litter and intercepted solar radiation, reducing the dominance of willow.  The flexibility of larch to mycorrhizal fungi for N-uptake promoted the biological invasion.  The contributor to N-deposits in the tephra was a native willow shrub, although the deposit was weakened by the biological invasion.  Therefore, the mycorrhizal N-transfer to plants was a key to determine the successional sere and belowground N dynamics.