Abstract: The impacts of nitrogen deposition on soil labile carbon at different age poplar plantations were examined in this study. Beginning in May 2012, we conducted a field experiment to simulate nitrogen deposition with five treatments at Dongtai Forest Farm in Jiangsu Province. In June 2013, the soil samples were taken to analyze the variations of soil labile organic carbon. The results indicated that soil microbial biomass carbon decreased after an initial increase with the increasing nitrogen level in the 5 and 9 years old poplar plantations, and increased with the increased nitrogen level in the 15 years old poplar plantation. Increasing the level of nitrogen enhanced the content of soil dissolved organic carbon in all poplar plantations. There was a significant correlation between the soil MBC and DOC. Furthermore, the soil MBC and DOC were significantly correlated with the soil TN, MBN, DON, NH₄⁺-N, NO₃^--N. Our results imply that nitrogen deposition might enhance the content of soil labile organic carbon, and thus affect the dynamics of soil organic carbon in the poplar plantations.

Key words: root morphology, fine root, root anatomy, N availability, mycorrhiza.