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.