Background
In a paper published in the same issue of Global Change Biology as that of Steinbeiss et al. (whose study is the object of this review), le Roux and McGeoch (2008) provide yet another example of what they describe as "the expansion of species distributions along their cooler boundaries in response to rising temperatures," which phenomenon, in their words, "appears to be a consistent biological consequence of recent climate warming," and which we have further indicated leads to increases in local biodiversity throughout the world, as noted in our review of le Roux and McGeoch's paper.

What was done
Working on the outskirts of Jena, Germany, the ten researchers sowed 20-m by 20-m plots of soil with seeds of either 1, 2, 4, 8, 16 or 60 species of either 1, 2, 3 or 4 plant functional groups (grasses, small herbs, tall herbs, and legumes), creating 16 replicate plots per species level except for the 16-species level plots (14 replicates) and the 60-species level plots (four replicates) in April of 2002, just before which soil carbon content sampling was performed, and after which similar sampling was repeated in April of 2004 and April of 2006.

What was learned
During the first two years of the study, soil carbon storage was limited to the top five cm of soil, while below ten cm depth, carbon was actually lost. After four years, however, carbon stocks had increased significantly within the top twenty cm of the soil. However, and "more importantly," in the words of Steinbeiss et al., "carbon storage significantly increased with sown species richness in all depth segments and even carbon losses were significantly smaller with higher species richness." Consequently, they concluded that "plant species richness ... accelerate[d] the build-up of new carbon pools within four years," and that "higher plant diversity mitigated soil carbon losses in deeper horizons."

What it means
In the words of the researchers who conducted the study, their findings suggest that "higher biodiversity might lead to higher soil carbon sequestration in the long-term," and, therefore, that "the conservation of biodiversity might play a role in greenhouse gas mitigation." We would merely add that this phenomenon represents a previously unrecognized negative feedback phenomenon, since studies such as that of le Roux and McGeoch have demonstrated that global warming typically leads to higher local and regional biodiversity wherever the process has been studied throughout the world.

Reference
Le Roux, P.C. and McGeoch, M.A. 2008. Rapid range expansion and community reorganization in response to warming. Global Change Biology 14: 2950-2962.