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Abstract

Soil organic matter (SOM) turnover
increasingly is conceptualized as a tension between
accessibility to microorganisms and protection from
decomposition via physical and chemical association
with minerals in emerging soil biogeochemical theory.
Yet, these components are missing from the original
mathematical models of belowground carbon dynamics
and remain underrepresented in more recent
compartmental models that separate SOM into discrete
pools with differing turnover times. Thus, a gap
currently exists between the emergent understanding
of SOM dynamics and our ability to improve terrestrial
biogeochemical projections that rely on the
existing models. In this opinion paper, we portray
the SOM paradigm as a triangle composed of three
nodes: conceptual theory, analytical measurement,
and numerical models. In successful approaches, we
contend that the nodes are connected—models capture
the essential features of dominant theories while
measurement tools generate data adequate to parameterize and evaluate the models—and balanced—models can inspire new theories via emergent behaviors,
pushing empiricists to devise new measurements.
Many exciting advances recently pushed the boundaries
on one or more nodes. However, newly integrated
triangles have yet to coalesce. We conclude that
our ability to incorporate mechanisms of microbial
decomposition and physicochemical protection into
predictions of SOM change is limited by current
disconnections and imbalances among theory, measurement,
and modeling. Opportunities to reintegrate
the three components of the SOM paradigm exist by carefully considering their linkages and feedbacks at specific scales of observation.