Abstract Dissolved organic carbon (DOC) pools can be considered as suitable indicators of soil quality that are very sensitive to different soil management practices. In this research controlled chambers were used to investigate the effects of elevated atmospheric CO2 concentrations (350 vs. 760 ppm) under two level of nitrogen fertilizer (0 vs. 200 kg N ha-1) and two different plant residues (alfalfa residue and wheat straw) on DOC of two calcareous and non calcareous soils. The results showed that elevated CO2 significantly increased DOC in calcareous and non calcareous soils. In the soils that received high rates of nitrogen fertilizer, release of DOC at elevated and ambient CO2 increased by approximately 30% compared to soils without nitrogen fertilizer. The amount of DOC tended to be affected by organic matter in both elevated and ambient CO2. In calcareous soil exposed to elevated and ambient CO2, concentration of DOC in samples received high or none N fertilizer were always higher than non-calcareous soil. From the obtained results, we concluded that release of DOC in elevated CO2 is controlled by multifactors such as soil organic matter, N and CaCO3 levels of soils.

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