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Hungate BA, Jackson RB, Field CB, Chapin III FS (1995) Detecting changes in soil carbon in CO2 enrichment experiments. Plant and Soil 187(2): 135-145.Read Abstract
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After four growing seasons, elevated CO<sub>2</sub> did not significantly alter surface soil C pools in two intact annual grasslands. However, soil C pools in these systems are large compared to the likely changes caused by elevated CO<sub>2</sub>. We calculated statistical power to detect changes in soil C, using an approach applicable to all elevated CO<sub>2</sub> experiments. The distinctive isotopic signature of the fossil-fuel-derived CO<sub>2</sub> added to the elevated CO<sub>2</sub> treatment provides a C tracer to determine the rate of incorporation of newly-fixed C into soil. This rate constrains the size of the possible effect of eievated CO<sub>2</sub> on soil C. Even after four years of treatment, statistical power to detect plausible changes in soil C under elevated CO<sub>2</sub> is quite low. Analysis of other elevated CO<sub>2</sub> experiments in the literature indicates that either CO<sub>2</sub> does not affect soil C content, or that reported CO<sub>2</sub> effects on soil C are too large to be a simple consequence of increased plant carbon inputs, suggesting that other mechanisms are involved, or that the differences are due to chance. Determining the effects of elevated CO<sub>2</sub> on total soil C and long-term C storage requires more powerful experimental techniques or experiments of longer duration.