Articles | Volume 1, issue 1
SOIL, 1, 313–330, 2015

Special issue: An introduction to SOIL

SOIL, 1, 313–330, 2015

Review article 09 Apr 2015

Review article | 09 Apr 2015

Investigating microbial transformations of soil organic matter: synthesizing knowledge from disparate fields to guide new experimentation

S. A. Billings1, L. K. Tiemann2, F. Ballantyne IV3, C. A. Lehmeier1, and K. Min1 S. A. Billings et al.
  • 1Department of Ecology and Evolutionary Biology and the Kansas Biological Survey, University of Kansas, Lawrence, KS, USA
  • 2Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing, MI, USA
  • 3Odum School of Ecology, University of Georgia, Athens, GA, USA

Abstract. Discerning why some soil organic matter (SOM) leaves soil profiles relatively quickly while other compounds, especially at depth, can be retained for decades to millennia is challenging for a multitude of reasons. Simultaneous with soil-specific advances, multiple other disciplines have enhanced their knowledge bases in ways potentially useful for future investigations of SOM decay. In this article, we highlight observations highly relevant for those investigating SOM decay and retention but often emanating from disparate fields and residing in literature seldom cited in SOM research. We focus on recent work in two key areas. First, we turn to experimental approaches using natural and artificial aquatic environments to investigate patterns of microbially mediated OM transformations as environmental conditions change, and highlight how aquatic microbial responses to environmental change can reveal processes likely important to OM decay and retention in soils. Second, we emphasize the importance of establishing intrinsic patterns of decay kinetics for purified substrates commonly found in soils to develop baseline rates. These decay kinetics – which represent the upper limit of the reaction rates – can then be compared to substrate decay kinetics observed in natural samples, which integrate intrinsic decay reaction rates and edaphic factors essential to the site under study but absent in purified systems. That comparison permits the site-specific factors to be parsed from the fundamental decay kinetics, an important advance in our understanding of SOM decay (and thus persistence) in natural systems. We then suggest ways in which empirical observations from aquatic systems and purified substrate–enzyme reaction kinetics can be used to advance recent theoretical efforts in SOM-focused research. Finally, we suggest how the observations in aquatic and purified substrate–enzyme systems could be used to help unravel the puzzles presented by oft-observed patterns of SOM characteristics with depth, as one example of the many perplexing SOM-related problems.

Short summary
We highlight observations relevant to soil organic matter (SOM) decay and retention but often emanating from disparate fields. First, we describe relevant natural and artificial aquatic environments. Second, we describe how intrinsic patterns of decay kinetics for purified soil substrates are useful for defining baseline rates. Third, we describe theoretical advances important for the discipline. Last, we describe how these advances can be used to unravel the mysteries of deep SOM persistence.
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