This 10-page paper by Cynthis M. Kallenbach, Serita D. Frey and A. Stuart Grandy was published in the November 2016 Nature Communications, 7:13630 DOI: 10.1038/ncomms13630
Summary: For nearly a century soil organic matter (SOM) formation has been depicted primarily as a function of the preservation of biologically stable complex plant compounds. Yet it has been known that soil microbial communities are adept at decomposing such materials, incorporating the released carbon into their microbial biomass. Due to advances in laboratory molecular analytic techniques, the role of microbes in SOM formation has been increasingly recognized. But direct evidence about the degree to which microbes are involved has been lacking. Now, a team of University of New Hampshire scientists has uncovered evidence that microbial pathways are the chief source of the organic matter found in stable soil carbon pools. They suggest that SOM is formed by residues of microbial digestion of carbon from roots and root exudates.
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