Carbon fluxes and the carbon budget in agroecosystems on agro-gray soils of the forest-steppe in the Baikal region

Field studies devoted to the transformation of the carbon cycle in agroecosystems on agro-gray soils (including soils contaminated with fluorides from aluminum smelters) in dependence on the changes in the hydrothermic conditions were performed for the first time within the framework of the long-term (1996–2010) soil monitoring in the forest-steppe zone of the Baikal region. The major attention was paid to the impact of the environmental factors on the synthesis and microbial destruction of organic carbon compounds. Certain differences in the fluxes and budget of carbon were found for the plots with cereal and row crops and for the permanent and annual fallow plots. The adverse effect of fluorides manifested itself in the enhanced C-CO₂ emission under unfavorable water and temperature conditions. The long-term average C-CO₂ emission from the soils contaminated with fluorides in agroecosystems with wheat after fallow was higher than that from the uncontaminated soil (179 and 198 g of C/m², respectively) and higher than that in the agroecosystems with a potato monoculture (129 and 141 g of C/m², respectively). At the same time, no significant variations in the content of the carbon of the microbial biomass (C_micr) in dependence on the environmental factors were found. The utilization of carbon for respiration and for growth of the soil microorganisms on the contaminated soil were unbalanced in particular years and for the entire period of the observations. The ratio between the fluxes of the net mineralized and re-immobilized carbon was used for the integral assessment of the functioning regime of the agroecosystems and the loads on them. Independently from the soil contamination with fluorides, the loads on the agroecosystems with wheat were close to the maximum permissible value, and the loads on the agroecosystems with potatoes were permissible. It was shown that the carbon deficit in the uncontaminated soils was similar under the wheat and potatoes (?30 and ?28 g of C/m², respectively). In the contaminated soils, it was higher under the potato monoculture and reached ?41 g of C/m².