What was done
The authors report the responses of belowground nematode herbivores to atmospheric CO2 enrichment to approximately 350 ppm above ambient in experiments conducted on three grassland ecosystems in Colorado and California (USA) and Montpellier, France.

What was learned
With respect to the soils involved, Ayres et al. state that "soil moisture increased in response to elevated CO2 in the California, Colorado, and French stud[ies] (Hungate et al., 1997; Nijs et al., 2000; Morgan et al., 2004)." With respect to the plants involved, they state that "elevated CO2 increased root biomass by approximately 3-32% in the first 5 years of the Coloradoan study (Pendall et al., 2004), by 23% after 6 years in the Californian study (Rillig et al., 1999), and by 31% after 6 months in the French study (Dhillion et al., 1996)." With respect to the nematodes involved, they state that "CO2 enrichment did not significantly affect the family richness, diversity, or PPI [plant parasitic nematode index] of herbivorous nematodes in the Colorado, California, or French study," noting that "in each experiment, neutral effects were the most frequent response to CO2 enrichment."

What it means
The seven researchers state that "one consequence of increased root production, without changes in belowground herbivore populations, might be greater plant inputs to soil," which "may lead to greater soil organic matter pools in grassland ecosystems, potentially enhancing soil carbon sequestration."

References
Dhillion, S.D., Roy, J. and Abrams, M. 1996. Assessing the impact of elevated CO2 on soil microbial activity in a Mediterranean model ecosystem. Plant & Soil 187: 333-342.

Hungate, B.A., Holland, E.A., Jackson, R.B., Chapin, F.S., Mooney, H.A. and Field, C.B. 1997. The fate of carbon in grasslands under carbon dioxide enrichment. Nature 388: 576-579.

Morgan, J.A., Mosier, A.R., Milchunas, D.G., LeCain, D.R., Nelson, J.A. and Parton, W.J. 2004. CO2 enhances productivity, alters species composition, and reduces digestibility of shortgrass steppe vegetation. Ecological Applications 14: 208-219.

Nijs, I., Roy, J., Salager, J.-L. and Fabreguettes, J. 2000. Elevated CO2 alters carbon fluxes in early successional Mediterranean ecosystems. Global Change Biology 6: 981-994.

Pendall, E., Mosier, A.R. and Morgan, J.A. 2004. Rhizodeposition stimulated by elevated CO2 in a semiarid grassland. New Phytologist 162: 447-458.

Rillig, M.C., Field, C.B. and Allen, M.F. 1999. Soil biota responses to long-term atmospheric CO2 enrichment in two California annual grasslands. Oecologia 119: 572-577.