Effects of past, present and future atmospheric CO"2 concentrations on soil organic matter dynamics in a chaparral ecosystem [An article from: Soil Biology and Biochemistry]

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Description:
Owing to the continuously increasing concentration of atmospheric CO"2, it has become a priority to understand if soil organic matter (SOM) will behave as a sink or a source of CO"2 under future environmental changes. Although many studies have addressed this question, a clear understanding is still missing, particularly with respect to long-term responses. In this study, we quantified soil C stores and dynamics in relationship to soil aggregation and pool composition in a Californian chaparral ecosystem exposed for 6 years to a gradient of atmospheric CO"2 concentrations, ranging from pre-industrial levels 250 to 750@mll^-^1 CO"2. Fossil fuel-derived CO"2 depleted in ^1^3C was used for the fumigation, thus providing a tracer of C input from the vegetation to the soil. Long-term CO"2 exposure invariably affected soil aggregation, with a significant decrease in the macroaggregate fraction at highest CO"2 levels relative to the other two size fractions (i.e. microaggregates and silt and clay). This soil structural change most likely reduced the stability and protection of SOM, and C content generally decreased in most fractions over the CO"2 treatments, and induced faster turnover of recently fixed C at high CO"2 levels. The strongest response was found in the C content of the microaggregates, which decreased significantly (P