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The Long-Term Fate of Organic Carbon in Semiarid Grassland Soil
Zhou, X., Chen, C., Wang, Y, Smaill, S. and Clinton, P. 2013. Warming rather than increased precipitation increases soil recalcitrant organic carbon in a semiarid grassland after 6 years of treatments. PLOS ONE 8: e53761.

In introducing their study, the authors write that "the world's soils contain twice as much carbon as the atmosphere (Batjes, 1996)," and that "as a result, even minor soil organic carbon (SOC) losses from the soils can greatly enhance carbon dioxide concentrations in the atmosphere, which [could] have a positive feedback on climate (IPCC, 2007)." Thus, they state that an "improved understanding of changes in soil recalcitrant organic carbon in response to global warming is critical for predicting changes in [total] SOC storage."

What was done
In the hope of helping to provide some of that "improved understanding," Zhou et al. say they "took advantage of a long-term field experiment with increased temperature and precipitation" - which was established in late April 2005 in a semiarid temperate steppe in Duolun County, Inner Mongolia, China - "to investigate the effects of warming, increased precipitation and their interactions on SOC fraction" by quantifying "labile SOC, recalcitrant SOC and stable SOC at 0-10 and 10-20 cm depths."

What was learned
The results of the efforts of the five researchers revealed that "neither warming nor increased precipitation affected total SOC and stable SOC at either depth," but that "increased precipitation significantly increased labile SOC at the 0-10 cm depth" and that "warming decreased labile SOC and marginally but significantly increased recalcitrant SOC at the 10-20 cm depth." And they say there were also "significant interactive effects of warming and increased precipitation on labile SOC and recalcitrant SOC at the 0-10 cm depths."

What it means
When all was said and done - and the several pluses and minuses accounted for - Zhou et al. concluded that "given that the absolute increase of SOC in the recalcitrant SOC pool was much greater than the decrease in labile SOC, and that the mean residence time of recalcitrant SOC is much greater, our results suggest that soil C storage at 10-20 cm depth may increase with increasing temperature in this semiarid grassland," which thus represents a net negative feedback on predicted global warming.

Batjes, N.H. 1996. Total carbon and nitrogen in the soils of the world. European Journal of Soil Science 47: 151-163.

IPCC. 2007. IPCC Working Group I. Climate Change 2007: The Physical Science Basis. Cambridge University Press, Cambridge, United Kingdom.

Reviewed 17 July 2013