Inorganic Carbon Removal from Alkaline Soils: an Underappreciated Influence on Soil Organic Carbon Measurements in an Elevated CO2 Experiment

Isolating soil organic carbon (SOC) from soil inorganic carbon (SIC) is necessary to quantify SOC stocks and understanding SOC dynamics. Inorganic acids are commonly used to remove SIC and several methods have been developed to minimize the impacts these acid treatments have on the residual SOC. Negative impacts on the SOC pool, such as underestimating SOC stocks, are caused in part due to differences in the amount and composition of the organic matter pool. The effects of SIC removal on SOC are often ignored within experimental studies based on the assumption that soils from the same site do not differ enough to impact results. However, some experimental treatments, such as elevated atmospheric CO2, change SOC pools in both concentration and composition. Therefore, SIC removal can introduce different biases in control and treatment soils that may differ by method. In this work, we compare two commonly used methods of SIC removal on a set of soil samples from the same elevated CO2 experiment. We use soils from the Nevada Desert Free Air Carbon dioxide Enrichment Facility to quantify how SIC removal with either acid washing or acid fumigation affect SOC in control and elevated CO2 plots. We then use the difference in SOC (