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Changes in nitrate (a) and ammonium (b) concentrations in soil microcosms incubated with 13CO2 or 12CO2 or 13CO2 plus C2H2 for 28 and 56 days. The soil microcosms were fertilized with 100 μg urea-N g−1 dws on a weekly basis. Error bars represent standard errors of triplicate microcosms. The same letter above different bars indicates no significant difference (P > 0.05).
