摘要 : Nitrogen (N) and carbon (C) isotopic signatures (delta N-15 and delta C-13) serve as powerful tools for understanding temporal changes in ecosystem processes, but how these signatures change across boreal forest chronosequences is... 展开 Nitrogen (N) and carbon (C) isotopic signatures (delta N-15 and delta C-13) serve as powerful tools for understanding temporal changes in ecosystem processes, but how these signatures change across boreal forest chronosequences is poorly understood. The delta N-15, delta C-13, and C/N ratio of foliage of eight dominant plant species, including trees, understory shrubs, and a moss, as well as humus, were examined across a 361 years fire-driven chronosequence in boreal forest in northern Sweden. The delta C-13 and C/N ratio of plants and humus increased along the chronosequence, suggesting increasing plant stress through N limitation. Despite increasing biological N fixation by cyanobacteria associated with feather mosses, delta N-15 showed an overall decline, and delta N-15 of the feather moss and associated vascular plants diverged over time from that of atmospheric N-2. Across this chronosequence the N fixed by cyanobacteria is unlikely to be used by mosses and vascular plants without first undergoing mineralization and mycorrhizal transport, which would cause a change in delta N-15 signature due to isotopic fractionation. The decreasing trend of delta N-15 suggests that as the chronosequence proceeds, the plants may become more dependent on N transferred from mycorrhizal fungi or from N deposition. 收起