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Soil Organic Carbon Response to Late 20th-Century Warming in the United Kingdom
Hopkins, D.W., Waite, I.S., McNicol, J.W., Poulton, P.R., Macdonald, A.J. and O'Donnell, A.G. 2009. Soil organic carbon contents in long-term experimental grassland plots in the UK (Palace Leas and Park Grass) have not changed consistently in recent decades. Global Change Biology 15: 1739-1754.

One of the postulated consequences of global warming is a loss of soil organic carbon (SOC). In probing this matter, Bellamy et al. (2005) used data from the National Soil Inventory of England and Wales, obtained between 1978 and 2003, "to show that carbon was lost from soils across England and Wales over the survey period at a mean rate of 0.6% yr-1 (relative to the existing soil carbon content)." This finding suggested to them that there was "a link to climate change," which further suggested, in their words, "that losses of soil carbon in England and Wales -- and by inference in other temperate regions -- are likely to have been offsetting absorption of carbon by terrestrial sinks."

What was done
Because changes in agricultural land management affect SOC contents, and because Bellamy et al. (2005) made no adjustments for such changes in their study, Hopkins et al. decided to explore this aspect of the subject using, as they describe it, "two sets of long-term experimental plots which have been under constant and known management for over a century and for which historical data exist that allow comparison over recent decades to determine what, if any, changes in SOC have occurred." These unique plots were the Palace Leas Meadow Hay Plots in northeast England, which were established in 1897, and the plots of the Park Grass Continuous Hay Experiment established in 1856 at Rothamsted in southeast England.

What was learned
Hopkins et al. determined "there were no significant differences between 1982 and 2006 for the Palace Leas plots or between 1959 and 2002 for the Park Grass plots," concluding therefore that "there has been no consistent decrease in SOC stocks in surface soils under old, permanent grassland in England in recent decades, even though meteorological records for both sites indicate significant warming of the soil and air between 1980 and 2000."

What it means
The six scientists say their observations lead them to "question whether for permanent grassland in England, losses in SOC in recent decades reported elsewhere [by Bellamy et al. (2005)] can be attributed to widespread environmental change," challenging even the idea that there were any SOC losses. As for why they found this to be the case, they speculate that "the lack of a consistent decline in SOC content linked to increased soil temperature since 1980 may be due to a compensatory increase in primary production," citing the work of Jenkinson et al. (1991), which is something that would logically be expected to occur in a CO2-accreting atmosphere.

Bellamy, P.H., Loveland, P.J., Bradley, R.I., Lark, R.M. and Kirk, G.J.D. 2005. Carbon losses from all soils across England and Wales 1978-2003. Nature 437: 245-248.

Jenkinson, D.S., Adams, D.E. and Wild, A. 1991. Model estimates of CO2 emissions from soil in response to global warming. Nature 351: 304-306.

Reviewed 16 September 2009