What was done
Open-top chambers maintained at atmospheric CO2 concentrations of 350 and 700 ppm were erected upon a regenerating oak-palmetto scrub ecosystem in Florida, USA, to study the effects of elevated CO2 on productivity and growth in this specialized community.  This paper describes the effects of elevated CO2 on the decomposition of ambient- and elevated-CO2-produced roots following 2.2 years of incubation in chamber soils, which were nutrient-poor and often water-stressed.

What was learned
Elevated CO2 did not significantly affect the decomposition rates of fine roots originating from either the ambient or CO2-enriched environments, even after more than two years of incubation.  However, atmospheric CO2 enrichment did increase the immobilization of nitrogen within decomposing fine roots.

What it means
As the air's CO2 content rises, the decomposition rates of fine roots in this scrub oak ecosystem will probably change very little from what they are currently.  However, because elevated CO2 enhanced fine root length densities in this community (Day et al., 1996), total soil carbon contents should increase with increases in the atmospheric CO2 concentration.  In addition, it is likely that nitrogen immobilization within decomposing fine roots will increase, which in the words of the authors "is a potential mechanism for nitrogen conservation for this system in a elevated CO2 world."

Reference
Day, F.P., Weber, E.P., Hinkle, C.R. and Drake, B.G.  1996.  Effects of elevated atmospheric CO2 on fine root length and distribution in an oak-palmetto scrub ecosystem in central Florida.  Global Change Biology 2: 143-148.