Organic matter is critical to how soil functions. It affects numerous biological, physical, and chemical processes in soil. It is not only a large reservoir of plant essential nutrients and minerals, but also a reservoir of organic carbon. The organic carbons compounds that make up this reservoir are highly diverse and numerous in their individual structures. My dissertation explores how the diversity of organic compounds in soil is impacted by ecosystem conditions, duration of decomposition, and microbial community structure. I use high resolution mass spectrometry to quantify dissolved organic matter molecular diversity in (i) different ecosystems, (ii) over time, and (iii) in response to variable microbial communities. To this end, I show that dissolved organic matter molecular diversity decreases over long periods of time and despite the overall decline in diversity, there are site-specific compounds that accumulate with depth in different ecosystems. Assessment of molecular diversity over shorter periods of time shows that microorganisms initially decrease the number of unique compounds in dissolved organic matter but increase the diversity of molecular properties at the same time. Finally, I conclude that the diversity of organic matter is influenced more by the metabolic potential of the decomposing microbial community rather than by differing plant litter inputs or microbial richness itself. How these changes in molecular diversity impact soil organic carbon persistence remains an important question for soil scientists to study further.