[delta]~(15)N in fine roots of Cunninghamia lanceolata plantations of different ages and implications for soil nitrogen cycling rates

Nitrogen( N) is an essential nutrient to plants. However,increasing N deposition into forest ecosystems due to will result in N saturation. The aims of this study were to( 1) measure the composition of stable nitrogen isotope( [delta]~(15)N) in fine roots in Cunninghamia lanceolata plantations at different ages and of various root orders,( 2) examine whether the stable isotopes( [delta]~(15)N) of fine roots in different orders were representative of the relative rates of soil net nitrogen( N)mineralization / nitrification across stands at different ages,and( 3) determine whether fine root [delta]~(15)N could be used as a better indicator of the rate of soil N cycling than foliar [delta]~(15)N. We analyzed the [delta]~(15)N of fine roots and leaves in C. lanceolata plantations at 3,8,14,21,and 46 years of age in subtropical China and carried out a 28-day laboratory incubation to analyze soil potential net N mineralization and nitrification rates. The results showed that there were significant differences in th