Changes in stable nitrogen and carbon isotope ratios of plants and soil across a boreal forest fire chronosequence
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Background and Aim
Nitrogen (N) and carbon (C) isotopic signatures (δ15N and δ13C) serve as powerful tools for understanding temporal changes in ecosystem processes, but how these signatures change across boreal forest chronosequences is poorly understood.
The δ15N, δ13C, 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 δ13C 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, δ15N showed an overall decline, and δ15N of the feather moss and associated vascular plants diverged over time from that of atmospheric N2.
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 δ15N signature due to isotopic fractionation. The decreasing trend of δ15N suggests that as the chronosequence proceeds, the plants may become more dependent on N transferred from mycorrhizal fungi or from N deposition.
KeywordsBoreal forest Chronosequence Pleurozium schreberi Mycorrhiza N2 fixation
We thank Morgan Karlsson for sample collection in this study. We also thank Keisuke Koba and two anonymous reviewers for valuable comments on an earlier draft of this manuscript. This study was supported by grants from Vetenskapsrådet to DW, FORMAS to MCN, and the Research Institute for Humanity and Nature (Japan) and JSPS, as well as by Special Coordination funds for Promoting Sciences and Technology from the MEXT to FH. FH was supported as a postdoctoral researcher by the Japan Society of the Promotion of Science Fellowships for Research Abroad.
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