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Enchytraeid Worm Responses to CO2, Warming and Drought
Reference
Maraldo, K., Krogh, P.H., van der Linden, L., Christensen, B., Mikkelsen, T.N., Beier, C. and Holmstrup, M. 2010. The counteracting effects of atmospheric CO2 concentrations and drought episodes: Studies of enchytraeid communities in a dry heathland. Soil Biology & Biochemistry 42: 1958-1966.

Background
The authors write that small oligochaete worms known as enchytraeids "are widely distributed from the Arctic to tropical areas, and typically inhabit the organic horizon in soils," where they "contribute to the decomposition processes and nutrient mineralization," which activities have been shown to lead to enhanced nutrient availability and uptake by plants (Laakso and Setala, 1999; Cragg and Bardgett, 2001). Enchytraeids provide these benefits directly, as Maraldo et al. describe it, "by consuming large amounts of organic matter," and indirectly "by their feeding activity and modifications of soil structure." And they note, in this regard, that "the presence of enchytraeids is especially important in nutrient poor ecosystems," such as "temperate heathland and northern coniferous forests, where their biomass dominates the soil faunal community," citing the work of Cragg (1961) and Swift et al. (1998).

What was done
Working on a hilly nutrient-poor sandy soil with a dry heath/grassland cover at Brandbjerg, Denmark, the seven scientists conducted an experiment that was begun in October 2005 and extended through 2007. There they studied the individual and combined effects of (1) soil warming: a mean daily temperature increase of 0.3°C in winter and 0.7°C in summer at a depth of 5 cm, provided by a scaffolding that carried a curtain -- which reflected the outgoing infrared radiation from the soil/plant surface back toward the ground -- that was automatically pulled over the vegetation at sunset and retracted at sunrise, (2) drought: peak soil water content reductions of 11% and 13% compared to control plots in 2006 and 2007, provided by waterproof curtains that were automatically pulled over the vegetation during rain events, and (3) atmospheric CO2 enrichment: a CO2 concentration increase from 382 to 481 ppm, provided by a free-air CO2 enrichment or FACE system.

What was learned
Maraldo et al. report that their experimentally-imposed warming had no significant impact on enchytraeid biomass production; but they found that their drought treatment decreased it by 40%. On the other hand, the extra 99 ppm of CO2 stimulated enchytraeid biomass by 40%. And they remark that at certain times this latter phenomenon was "especially positive," as in the summer of 2007, when they say "the total enchytraeid biomass in the CO2 plots was increased by 108% compared to ambient plots." As for interactions among the three factors, they report there were none, so that "the positive effect of increased CO2 [+40%] and the negative effect of drought [-40%] were cancelled out when applied in combination."

What it means
In response to the claim of the world's climate alarmists that earth's future will be characterized by (1) rising temperatures, (2) an intensified hydrologic cycle, and (3) greater atmospheric CO2 concentrations, we can imagine the planet's enchytraeid worms joyfully shouting What more could we ask for? ... and the plants their activities benefit exclaiming Ditto!

References
Cragg, J.B. 1961. Some aspects of the ecology of moorland animals. Journal of Ecology 49: 477.

Cragg, R.G. and Bardgett, R.D. 2001. How changes in soil faunal diversity and composition within a trophic group influence decomposition processes. Soil Biology and Biochemistry 33: 2073-2081.

Laakso, J. and Setala, H. 1999. Sensitivity of primary production to changes in the architecture of belowground food webs. Oikos 87: 58-64.

Swift, M.J., Andren, O., Brussaard, L., Briones, M., Couteaux, M.M., Ekschmitt, K., Kjoller, A., Loiseau, P. and Smith, P. 1998. Global change, soil biodiversity, and nitrogen cycling in terrestrial ecosystems -- three case studies. Global Change Biology 4: 729-743.

Reviewed 19 January 2011