The Soil Science Society of America defines soil organic matter (SOM) as “the organic fraction of the soil exclusive of undecayed plant and animal residues” (Soil Science Society of America 2008). SOM, here used interchangeably with “humus,” is built upon a chemical backbone of carbon, hydrogen, and oxygen, but also contains other important elements including organic nitrogen, organic phosphorus, and organic forms of a number of trace elements. Ultimately, SOM is derived from senescent plant material, either produced autochthonously or produced allochthonously and captured by an ecosystem, which has been at least partially degraded by the decomposer community. As decomposers mineralize organic carbon substrates to fuel their metabolism, they simultaneously mineralize the organic nutrients necessary for subsequent plant and microbial growth. Thus, SOM represents an important link between plant and microbial activities within ecosystems.