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

Vestergård, Mette; Reinsch, Sabine; Bengtson, Per LU ; Ambus, Per and Christensen, Søren (2016) In Soil Biology and Biochemistry 100. p.140-148
Abstract

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... (More)

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.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Carbon-13, Drought, FACE, Global change, Heathland, Warming
in
Soil Biology and Biochemistry
volume
100
pages
9 pages
publisher
Elsevier
external identifiers
  • scopus:84974735951
  • wos:000380600100017
ISSN
0038-0717
DOI
10.1016/j.soilbio.2016.06.010
language
English
LU publication?
yes
id
d05e4a67-d496-4267-b2a7-eb9e4cef3c43
date added to LUP
2016-11-28 14:50:03
date last changed
2017-07-30 05:18:00
@article{d05e4a67-d496-4267-b2a7-eb9e4cef3c43,
  abstract     = {<p>Rising atmospheric CO<sub>2</sub> 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 CO<sub>2</sub> concentration profoundly. In many ecosystems, including the heath/grassland system studied here, increased plant production at elevated CO<sub>2</sub> 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 CO<sub>2</sub> 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 CO<sub>2</sub> 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 <sup>13</sup>C/<sup>12</sup>C signature that is distinct from that of the native SOC, which allowed us to assess the contribution of these two C sources to the CO<sub>2</sub> evolved. Sucrose induced priming of SOC, and the priming response was higher in soil exposed to long-term elevated CO<sub>2</sub> 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 CO<sub>2</sub> soil was assimilated before or after the initiation of the CO<sub>2</sub> treatment 8 years prior to sampling, because CO<sub>2</sub> concentrations were raised by fumigating the experimental plots with pure CO<sub>2</sub> that was <sup>13</sup>C-depleted compared to ambient CO<sub>2</sub>. Surprisingly, we conclude that sucrose addition primed decomposition of relatively old SOC fractions, i.e. SOC assimilated more than 8 years before sampling.</p>},
  author       = {Vestergård, Mette and Reinsch, Sabine and Bengtson, Per and Ambus, Per and Christensen, Søren},
  issn         = {0038-0717},
  keyword      = {Carbon-13,Drought,FACE,Global change,Heathland,Warming},
  language     = {eng},
  month        = {09},
  pages        = {140--148},
  publisher    = {Elsevier},
  series       = {Soil Biology and Biochemistry},
  title        = {Enhanced priming of old, not new soil carbon at elevated atmospheric CO<sub>2</sub>},
  url          = {http://dx.doi.org/10.1016/j.soilbio.2016.06.010},
  volume       = {100},
  year         = {2016},
}