What controls the depth profile and overall age of carbon in soils ?

Trumbore, S.*; Schrumpf, M.*; Khomo, L.*; Koarashi, Jun

no journal, , 

Carbon content usually declines, and its age increases, with depth in soil profiles. These patterns reflect the operation of several different depth-dependent processes. We compare the depth trends of carbon and C-14 in density-fractionated soils sampled from locations that vary in parent material/mineralogy and vegetation/climate and use whole-profile averages to identify patterns across a range of edaphic factors. The depth-profile of the free light fraction is similar to that of roots, and its age remains modern regardless of soil depth. In contrast, the radiocarbon age of C associated with minerals, or occluded within aggregates, increases in most soils almost linearly with depth. The slope of C-14 in the mineral fraction versus depth is potentially a metric useful for distinguishing among mechanisms responsible for C stabilization.