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Title: Response of soil carbon matter pools to elevated CO2 and warming in a semi-arid grassland

Author
item CARRILLO, YOLIMA - University Of Wyoming
item PENDALL, ELISE - University Of Wyoming
item DIJKSTRA, FEIKE - University Of Sydney
item Morgan, Jack
item NEWCOMB, JOANNE - University Of Wyoming

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2011
Publication Date: 6/17/2011
Citation: Carrillo, Y., Pendall, E., Dijkstra, F., Morgan, J.A., Newcomb, J.M. 2011. Response of soil carbon matter pools to elevated CO2 and warming in a semi-arid grassland. Plant and Soil. 347:339-350.

Interpretive Summary: As climate change unfolds and we learn more about its nature, a matter of no small concern is whether climate change will cause responses in Earth systems that feed-back and accelerate the current rate of climate change. One such concern is with Earth’s Carbon Cycle, which is sensitive to climate, and therefore has the potential to be altered by climate change and/or increases in atmospheric CO2. In a field experiment conducted in a mixed-grass prairie in Wyoming, ambient levels of CO2 and temperatures were increased to levels expected to occur in the second half of this century in order to evaluate how C in soil organic matter pools will respond under future conditions. Depending on the particular year, C pools responded to both CO2 and temperature, and the responses were related to the treatment effects on soil water as well as the size of plants. The responses suggest that so-called resistant soil C may be susceptible to increased losses in the future, which would reduce the ability of such grasslands to store C and off-set climate change. If this happens and is a common response in such semi-arid systems, then the combined effect of many world semi-arid systems could be to reduce the rate at which such grasslands assimilate C, which could feed-back and cause an acceleration of climate change.

Technical Abstract: Warming and elevated atmospheric CO2 (eCO2) can elicit contrasting responses on different SOM pools, thus to understand the effects of combined factors it is necessary to evaluate individual pools. Over two years, we assessed responses to eCO2 and warming of SOM pools, their susceptibility to decomposition, and whether these responses were mediated by plant inputs in a semi-arid grassland at the PHACE (Prairie Heating and CO2 Enrichment) experiment. We used long-term soil incubations and assessed relationships between plant inputs and the responses of the labile and resistant pools. We found strong and contrasting effects of eCO2 and warming on the labile C pool. In 2008 labile C was increased by eCO2 and was positively related to plant biomass. In contrast, in 2007 eCO2 and warming had interactive effects on the labile C, and the pool size was not related to plant biomass. Effects of warming and eCO2 in this year were consistent with treatment effects on soil moisture and temperature and their effects on labile C decomposition. The decomposition rate of the resistant C was positively related to indicators of plant C inputs. Our approach demonstrated that SOM pools in this grassland can have early and contrasting responses to climate change factors. The labile C pool in the mixed-grass prairie was highly responsive to eCO2 and warming but the factors behind such responses were highly dynamic across years. Results suggest that in this grassland the resistant C pool could be negatively affected by increases in plant production driven available soil C.