15N aboundance in nitrogen of naturally occurring substances and global assessment of denitrification from isotopic viewpoint.

Natural abundance of 15N in organic and inorganic nitrogenous substances in land was investigated. Available data on 15N abundance of biogenic nitrogen were summarized. Denitrification is divided into four types on the basis of the mode of isotope fractionation and environmental conditions. According to the simplified model on nitrogen isotope balance, the contribution of denitrification on land to the global denitrification is twice as much as that in the sea. The mode of 15N distribution in biogenic substances was discussed along the biogeochemical cycle of nitrogen with special reference to the fractionation of nitrogen isotopes occurring in denitrification and nitrogen fixation.