Description
In forest ecosystems tree girdling is a common method to partition fluxes of soil derived CO2 into autotrophic (e.g. root derived) and heterotrophic respiration (e.g. derived by SOM decomposition). However, in long term girdling experiments increasing root mortality provides new organic matter for decomposers. This could increase heterotrophic respiration, or even induce priming effects (stimulation of SOM decomposition), thus leading to an underestimation of autotrophic respiration. We investigated soil CO2 efflux and its 13C values over different time scales in a long-term girdling experiment and in non-girdled plots in a temperate beech (Fagus sylvatica) forest. Additionally we analysed ? 13C values of a comprehensive set of potential substrates and sources for soil respiration. Girdling decreased soil respiration by 36 % over the course of a year most significantly during the growing season. After the initiation of litterfall, soil respiration was mainly dominated by heterotrophic respiration, characterised by similar amounts of soil derived CO2 in both girdled and non-girdled plots. Further, girdling led to more depleted 13C signatures of soil derived CO2 by 1.5 on an annual and daily time scale, indicating reduced autotrophic respiration and a shift towards decomposition of root litter and SOM. This isotopic shift was corroborated by more depleted isotopic signatures of the dissolved organic carbon (DOC) pool in soils of girdled plots, also indicating increased decomposition processes and thus increased heterotrophic respiration. In controls, the ?13C of DOC was similar to that of root carbohydrates and enriched in 13C compared to girdled plots indicating that root exudates may contribute substantially to DOC. Further, bulk plant litter (leaf litter, fine and coarse root litter) as well as SOM were more depleted in 13C than plant carbohydrates (phloem sap sugars, root starch and sugars) and root respiration. This indicated that a major part of soil respiration was fuelled by recently fixed carbon.| Period | 2010 |
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| Event title | SINA - Stable Isotope Network Austria Meeting 2010 |
| Event type | Conference |
| Location | Seibersdorf, AustriaShow on map |