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Abstract

Current attempts to explain the persistence of carbon in soils focuses on explanations such as the
recalcitrant plant residues and the physical isolation of
substrates from decomposers. A pool of organic matter
that can persist for centuries to millennia is hypothesized
because of the evidence provided by the persistence of
pre-disturbance C in fallow or vegetation change
experiments, and the radiocarbon age of soil carbon.
However, new information, which became available
through advances in the ability to measure the isotope
signatures of specific compounds, favors a new picture
of organic matter dynamics. Instead of persistence of
plant-derived residues like lignin in the soil, the majority
of mineral soil is in molecules derived from microbial
synthesis. Carbon recycled multiple times through the
microbial community can be old, decoupling the radiocarbon
age of C atoms from the chemical or biological
lability of the molecules they comprise. In consequence
is soil microbiology, a major control on soil carbon
dynamics, which highlights the potential vulnerability of
soil organic matter to changing environmental conditions.
Moreover, it emphasizes the need to devise new management options to restore, increase, and secure this valuable resource.