Ecosystem Studies and Management
Carbon Storage in Soils
Scientist Sue Trumbore samples soil horizon depths.
While carbon sequestration in forest soils is generally low unless the forest is recovering from a disturbance, carbon sequestered in the soil is potentially more ‘permanent’ as a result of the way that soils protect carbon. Based largely on work by colleagues Julia Gaudinski (UC Santa Cruz) and Sue Trumbore (Max Planck Institute for Biogeochemistry), we estimated plausible carbon sequestration rates in the mineral soil and forest floor using bomb radiocarbon techniques. This technique is based on the fact that atmospheric testing of nuclear weapons in the 1950’s left a discernable 14C signature in the atmosphere. This signal can be followed in terrestrial ecosystems as this carbon is removed from the atmosphere by the vegetation, then cycled through the ecosystem as a result of litterfall, mortality, and other carbon fluxes to the soil.
Results
- We found that most of the carbon that entered the soil over the past 40 years is near the surface of the soil in either forest floor material or so-called ‘light fraction’ material in the surface mineral soils.
- Using these results, estimates of carbon inputs to the soil, and a model, we predict that the rates of carbon sequestration in soils are low, ranging from 0 to 0.3 Mg C ha-1. We cannot rule out the possibility that the soil is accumulating no carbon at all.
- If we take an average value of 0.15 Mg C ha-1, this is only about 10% of the observed annual net carbon uptake and storage in the live vegetation.
