Indirect effects of experimental warming on dissolved organic carbon content in subsurface peat
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The peatland carbon store is threatened by climate change and is expected to provide positive feedback on air temperature. Most studies indicate that enhanced temperature and microbial activities result in a rise of dissolved organic carbon (DOC) as a consequence of higher peat decomposition. Few of them, however, have investigated the impact of in situ experimental warming on DOC response.
Material and methods
We studied the response of DOC, dissolved organic nitrogen (DON), phenol oxidase, and fluorescein diacetate activities (FDA) to a 3-year in situ experimental warming using open-top chambers (OTCs) in a Sphagnum-dominated peatland.
Results and discussion
No significant warming of soil was recorded, implying that the simultaneous decrease in DOC and DON and the rise in FDA at the depths of 25 and 40 cm were not caused by the direct effect of OTCs on water temperature, but might instead have been mediated by plant root exudates. The water chemistry suggests that DOC production was compensated by in situ mineralization. We hypothesize that an increased hydrolysis of organic matter (OM) was counterbalanced by the mineralization of dissolved organic matter (DOM) and that microorganisms preferentially used labile compounds originating from increased root exudates.
This trade-off between production of DOC through hydrolysis and consumption in the process of mineralization shows (1) the limitation of using only DOC as an indicator of the sensitivity of peat decomposition to climate warming and (2) the need to improve our understanding of the indirect impact of root exudates.
KeywordsEnzymatic activities Hydrolysis Open-top chambers Organic matter Temperature
This work was funded as part of the PEATWARM research initiative through an ANR (French National Agency for Research) grant (ANR-07-VUL-010). This paper is a contribution to the research conducted in the Labex VOLTAIRE (ANR-10-LABX-100-01). The authors are also indebted to the Regional Scientific Council of Natural Heritage of the Franche-Comté Region for permitting access to Le Forbonnet site. The authors are grateful to E Rowley-Jolivet for revision of the English version. The authors also thank the two anonymous reviewers for their helpful suggestions.
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