Soil Respiration and the Carbon Sequestration Potential in Agroecosystems

Soil respiration (SR) is one of the main regulatory factors of the balance of organic carbon in soils and is closely related to the net primary (NPP), ecosystem (NEP), and biome (NBP) production of photosynthesis. An increase in the concentration of CO₂ in the atmosphere causes its fertilization and, as a result, an increase in annual NPP. The potential of carbon sequestration (PCS) in agroecosystems of the Russian Federation is considered. PCS in soils is predetermined by the soil formation conditions, which include the climate, the physicochemical properties of the soil-forming rock, and the type of ecosystem. In soils of natural ecosystems, a relative balance is maintained between the carbon sink into NBP and heterotrophic respiration (HR). In agroecosystems, this equilibrium is disrupted and HR predominates over NPP in the main. The actual PCS depends on the long-term balance between the amount of carbon entering the soil in the form of NPP and NEP on the one hand, and HR of soils on the other. Sequestered carbon in the soil can only be carbon that has passed the stage of humification. From the standpoint of the mean residence time in the soils of NPP (1–2 years) and NEP (up to ten years), the pools cannot be attributed to sequestered carbon, since these pools are in an active process of humification and dynamically lose C–CO₂ to the atmosphere due to HR. The assessment of the level of real sequestration of C in soils is determined by the ratio (balance) between the HR of the soil and the amount of new soil C-stock in the form of NBP. The long-term carbon balance in agriculture is analyzed, and the real potential of carbon sequestration by soils of agricultural lands of the Russian Federation for the period of 1960–2022 is estimated. During this period, a steady trend of increasing carbon deficiency in the soils remains in the soils under cultivation.