Carbon (C) and nitrogen (N) stoichiometry contributes to understanding elemental compositions and coupled biogeochemical cycles in ecosystems. However, we know little about the temporal patterns of C:N stoichiometry during forest development. The goal of this study is to explore the temporal patterns of intraspecific and ecosystem components' variations in C:N stoichiometry and the scaling relationships between C and N at different successional stages.
Along forest development in a natural temperate forest, northeastern China, four age gradients were categorized into ca. 10-, 30-, 70- and 200-year old, respectively, and three 20m×20m plots were set up for each age class. Leaves, branches, fine roots and fresh litter of seven dominant species as well as mineral soil at depth of 0-10cm were sampled. A Universal CHN Elemental Analyzer was used to determine the C and N concentrations in all samples.
Intraspecific leaf C, N and C:N ratios remained stable along forest development regardless of tree species; while C, N concentrations and C:N ratios changed significantly either in branches or in fine roots, and they varied with tree species except Populus davidiana (P < 0.05). For ecosystem components, we discovered that leaf C:N ratios remained stable when stand age was below ca. 70-yr and dominant tree species were light-demanding pioneers such as Betula platyphylla and Populus davidiana, while increased significantly at the age of ca. 200-yr with Pinus koraiensis as the dominant species. C:N ratios in branches and fresh litter did not changed significantly along forest development stages. C concentrations scaled isometrically with respect to N concentrations in mineral soil but not in other ecosystem components. Our results indicate that, leaf has a higher intraspecific C:N stoichiometric stability compared to branch and fine root, whereas for ecosystem components, shifts in species composition mainly affect C:N ratios in leaves rather than other components. This study also demonstrated that C and N remain coupled in mineral soils but not in plant organs or fresh litter during forest development.