Enhanced priming of old, not new soil carbon at elevated atmospheric CO2

Vestergard, Mette; Reinsch, Sabine ORCID: https://orcid.org/0000-0003-4649-0677; Bengtson, Per; Ambus, Per; Christensen, Soren. 2016 Enhanced priming of old, not new soil carbon at elevated atmospheric CO2. Soil Biology and Biochemistry, 100. 140-148. https://doi.org/10.1016/j.soilbio.2016.06.010

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Abstract/Summary

Rising atmospheric CO2 concentrations accompanied by global warming and altered precipitation patterns calls for assessment of long-term effects of these global changes on carbon (C) dynamics in terrestrial ecosystems, as changes in net C exchange between soil and atmosphere will impact the atmospheric CO2 concentration profoundly. In many ecosystems, including the heath/grassland system studied here, increased plant production at elevated CO2 increase fresh C input from litter and root exudates to the soil and concurrently decrease soil N availability. Supply of labile C to the soil may accelerate the decomposition of soil organic C (SOC), a phenomenon termed ‘the priming effect’, and the priming effect is most pronounced at low soil N availability. Hence, we hypothesized that priming of SOC decomposition in response to labile C addition would increase in soil exposed to long-term elevated CO2 exposure. Further, we hypothesized that long-term warming would enhance SOC priming rates, whereas drought would decrease the priming response. We incubated soil from a long-term, full-factorial climate change field experiment, with the factors elevated atmospheric CO2 concentration, warming and prolonged summer drought with either labile C (sucrose) or water to assess the impact of labile C on SOC dynamics. We used sucrose with a 13C/12C signature that is distinct from that of the native SOC, which allowed us to assess the contribution of these two C sources to the CO2 evolved. Sucrose induced priming of SOC, and the priming response was higher in soil exposed to long-term elevated CO2 treatment. Drought tended to decrease the priming response, whereas long-term warming did not affect the level of priming significantly. We were also able to assess whether SOC-derived primed C in elevated CO2 soil was assimilated before or after the initiation of the CO2 treatment 8 years prior to sampling, because CO2 concentrations were raised by fumigating the experimental plots with pure CO2 that was 13C-depleted compared to ambient CO2. Surprisingly, we conclude that sucrose addition primed decomposition of relatively old SOC fractions, i.e. SOC assimilated more than 8 years before sampling.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.1016/j.soilbio.2016.06.010
UKCEH and CEH Sections/Science Areas:	Emmett
ISSN:	0038-0717
Additional Keywords:	carbon-13, drought, FACE, global change, heathland, warming
NORA Subject Terms:	Agriculture and Soil Science
Date made live:	28 Jun 2016 09:52 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/513847

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