Fine root mass in relation to soil N supply in a cool temperate forest

Soil inorganic nitrogen supply and fine root mass in the top layers of mineral soil (0–5 and 5–10 cm) were investigated at upper and lower sites of a cool temperate forest where Fagus crenata and Quercus crispula dominate. At both sites, soil inorganic nitrogen supply was greatest in the 0–5 cm layer. The predominant forms of soil inorganic nitrogen supply were NH4 +-N at the upper site and NO3−-N at the lower site. Fine roots were concentrated in the 0–5 cm layer at the upper site, but not at the lower site. The form of supplied soil inorganic nitrogen supply can be important in determining the vertical distribution of fine roots.