The majority of terrestrial (land-based) carbon is stored in soil. With changes in climate and land use, understanding this key player in the carbon cycle is increasingly important. In October 2014, a group of scientists from 13 countries gathered in South Carolina for the Sixth International Workshop on Soil and Sedimentary Organic Matter Stabilization and Destabilization (SOM6). Participants engaged in focused discussions and shared results from research funded by USDA, NSF, DOE, USGS, and NOAA, among other sources. USDA’s National Institute of Food and Agriculture was a major supporter of the workshop, allowing participation from many students and post-doctoral researchers who otherwise would not be able to attend.

An important thread that has surfaced within the research community involved in SOM6 is the understanding that carbon storage is mediated by microorganisms (microbes) living in the soil, which in turn can be influenced by land management practices and plant biodiversity. For example, USDA-funded research at Michigan State University’s Kellogg Biological Station (an NSF Long-Term Ecological Research site) found that soil accumulated significantly more carbon under organic farming conditions than under conventional farming practices—even though organically farmed soils may be
tilled more frequently and may receive less carbon from plant residues. This counterintuitive finding is attributed to the higher biomass, activity, and growth efficiency of microbes in organic sites, a difference associated with higher biodiversity among the plants being grown. Moreover, long-term datasets from grassland ecosystems showed that higher biodiversity resulted in more carbon reaching the microbial communities that live around plant roots, increasing both microbial activity and soil carbon storage. Altogether, this suggests that ecosystem properties favoring the abun- dance, diversity, and activity of microbial communities are important to maximizing carbon storage in soil.