the availability of nitrogen in soil is one of the most important factors for tree growth. although tree species mixtures are known to increase forest productivity, it remains unclear how they affect soil nitrogen. in this thesis, i focus on the effects of tree species diversity on soil resident nitrogen, particularly ammoniacal nitrogen (nh4) and nitrate nitrogen (no3), through the review of 19 published papers. i also examined potential mechanisms associated with the influence of tree species diversity on soil nitrogen. i found a negative effect of tree species mixtures on the nitrogen concentration of soil. my goal was to evaluate the effects of tree species diversity on nitrogen in soil by comparing the soil traits of monocultures and species mixtures. i found that there were no significant differences in the effects on no3 and nh4 in the soils of species mixtures compared to monocultures. my results suggested that despite increased nitrogen uptake by trees in species mixtures, the availability of nitrogen in soil did not decrease in species mixtures, which was likely due to increased nitrogen resorption, retention, and fixation.