ARS | Publication request: Changes in soil organic matter and inorganic C after five years of doubled CO2 in a semi-arid grassland

Submitted to: Soil Science Society of America Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: August 15, 2006
Publication Date: November 12, 2006
Citation: Pendall, E., Reeder, S.J., Mosier, A., Morgan, J.A. 2006. Changes in soil organic matter and inorganic C after five years of doubled CO2 in a semi-arid grassland. Soil Science Society of America Annual Meeting. CDROM.

Technical Abstract: Elevated atmospheric CO2 may lead to increased C sequestration in terrestrial ecosystems if the C is stored in long-lived pools such as organic matter and soil minerals. Above- and belowground primary production were stimulated by elevated CO2 in an open-top chamber (OTC) experiment on a semi-arid grassland ecosystem in northeastern Colorado. We evaluated responses of soil organic and inorganic C after five years of experimental treatment by excavating soil monoliths to 75-cm depth. Soil organic matter (SOM) was partitioned into water extractable, particulate and mineral associated portions, and organic and inorganic C content and isotopic composition were determined. We found no change in total SOM, but water soluble organic C was higher under the elevated CO2 treatment. Stable isotopes suggested that storage rate of new organic C averaged 30 g C m-2 y-1 in ambient chambers and 75 g C m-2 y-1 in elevated CO2 chambers. Inorganic C (IC) content increased substantially below 40-cm depth under elevated CO2, amounting to a doubling of the inorganic C content after 5 years. IC storage rate averaged 27 g C m-2 y-1 in ambient and 52 g C m-2 y-1 in elevated chambers, demonstrating the importance of this C pool in semi-arid systems. Total soil N content decreased by 70 g m-2 in the top 60-cm after 5 years of elevated CO2, suggesting “mining” of soil N to support increased plant growth. Soil electrical conductivity and pH also changed in response to the 5-year OTC experiment. Elevated CO2 thus affected the total soil environment, in addition to doubling C sequestration rates.