What was done
The authors studied carbon (C) and nitrogen (N) relations in the plants and moderately-fertile soil of a sandstone grassland at Stanford University's Jasper Ridge Biological Preserve in central California near the conclusion of a five-year study conducted between 1992 and 1997, where two CO2 treatments (360 and 720 ppm) were maintained within twenty open-top chambers (ten replicates per treatment).

What was learned
The increased concentration of atmospheric CO2 increased soil microbial biomass at the same time that it increased plant nitrogen uptake.  The net effect of these two phenomena was that less nitrogen was left in the soil for microbes to use, which resulted in decreased microbial respiration per unit biomass and, hence, decreased microbial decomposition and increased ecosystem carbon accumulation.

What it means
In the words of the authors, "this reduction in decomposition could cause terrestrial ecosystems to become net C sinks, especially if plants become more efficient at acquiring N from low C:N soil organic matter (for example, by increasing mycorrhizae)," which, we might add, plants typically do when exposed to elevated levels of atmospheric CO2 (see the many Journal Reviews posted under Fungi in our Subject Index).  Hence, the authors conclude that "carbon accumulation in the terrestrial biosphere could partially offset the effects of anthropogenic CO2 emissions on atmospheric CO2," as we have long claimed is likely to be the case (see our Editorials of 15 November 1998, 1 December 1999 and 30 August 2000).  The net result of the ongoing rise in the air's CO2 content should thus be a ratcheting-up of both plant prowess and the carbon-sequestering capacities of earth's soils, both of which phenomena are good news for the biosphere.