Changes in the carbon dioxide emission from soils in the course of postagrogenic succession in the Chernozems forest-steppe

The CO2 emission from soils in the course of the long-term postagrogenic succession on Calcic Chernozems under meadow-steppe vegetation was studied. Seasonal dynamics of the emission at different stages of the restoration of natural vegetation and long-term changes in the main pools of carbon in the soils and phytomass were examined. These data were used to create a regression model of the CO2 emission on the basis of data on the soil water content and temperature with a temporal resolution of 3 h. The results were compared with an analogous study of the postagrogenic succession on sandy Agropodzols of southern taiga. It was found that the long-term pattern of the CO2 emission has a bimodal character. The first maximum corresponds to the early stages of the succession (2–8 years) and is ensured by a sharp intensification of respiration in the organomineral soil horizons under the impact of plant species typical of these stages, active growth of their underground parts, and, probably, activation of microbiota in the rhizosphere. The second maximum of the emission is observed at the final stages of the succession and is mainly ensured by the increasing pool of steppe litter. A decrease in the soil temperature because of the thermal insulation of the soil surface by the accumulating litter and organic substances in the topsoil horizons leads to a temporary decrease in the emission intensity at the middle stages of the succession, when the litter pool is still not vary large. The restoration of the initial level of the CO2 emission typical of the natural cenoses is achieved in about 80–100 years after the abandoning of the cultivated fields, i.e., considerably faster than that in the southern taiga zone (150–170 years). The results of modeling suggest that this is caused by the considerable accumulation of steppe litter, organic substances, and phytomass in the topsoil horizons rather than by the somewhat increased heat supply owing to longer duration of vegetation season.