Role of calcium and nitrogen in stabilization of soilcarbon in forest soils

Brewer, E.A., E.A. Paul, and S.J. Morris

Presented at the All Scientist Meeting (2003-09-12 )

Carbon © sequestration in soils is important for soil fertility and may play a role in short-term mitigation of elevated CO2.  Unfortunately, the mechanisms for C stabilization are poorly understood.  Previous studies have determined that nitrogen (N) and soil cations, especially calcium (Ca), are essential to C storage.  Our research evaluates the importance of N and Ca in stabilization of soil C.  Laboratory incubations were established using soil from an afforested red pine plantation with relatively low C content. We chose this specific site because earlier field studies have suggested that soils under pine stands with higher Ca content have greater C sequestration. Incubated soils were amended with Ca, added at a rate consistent with adjacent high C soils and N at twice and six times atmospheric deposition rates for this area.  The N and Ca amendments were added separately and together with and without incorporation of litter. The addition of Ca in the form of lime increased the amount of CO2 lost in the first 95 days of incubation when compared to control soils.  The addition of N at either 2x or 6x decreased CO2 evolution over the first 30 days of incubation compared to the control.  Incorporation of litter increased CO2 evolution in all treatments, but lime additions consistently resulted in the greatest CO2 evolution.  Total CO2 evolution during the first 116 days from the lime treatments included less CO2 evolution, compared to control treatments, than can be accounted for by the addition of lime.  As the rates of evolution for these treatments do not currently differ, total C losses from the lime treatments suggest stabilization of soil C by Ca addition.  Increasing the incubation time will allow for better understanding of overall impacts of Ca on C.  Maximizing C sequestration by increasing stabilization may be achieved by Ca addition, but requires greater understanding of the mechanisms controlling C storage in soils.

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