Carbon Sequestration in Abandoned Lands

Soils of fallow ecosystems, formed on the former croplands abandoned from agricultural use, are the most important sinks of atmospheric carbon, that determines their key biospheric functions. Using a chronosequence approach, we studied postagrogenic changes in organic carbon (Corg) stocks, the structure of pools and stability of soil organic matter (OM), and their microbial and enzymatic activities within the former tillage horizon (0−20 cm) in three bioclimatic zones: southern taiga, broadleaf forests, and forest-steppe. During the postagrogenic restoration, carbon stocks increased in Albic Podzols of the southern taiga and Haplic Luvisols of the broadleaf forest zone by 1.2−1.4 times in soils abandoned for less than 20 years, and by 1.4−1.5 times in soil abandoned 20−45 years ago, as compared to the current arable soil. Thermogravimetric fractionation of OM in Haplic Luvisols of broadleaf forest and forest-steppe zones displayed the increase in Corg content in all identified OM pools: thermally labile, stable, and persistant. Recarbonization of the former tillage horizon during the postagrogenic succession was accompanied by pronounced OM stratification, determined by a more rapid increase in the labile OM pool in its topsoil (0−10 cm) compared to the depth below (10−20 cm). During the post-agrogenic evolution of former arable soils, the basic indicators of the microbial community state and the total pool of hydrolytic enzymes gradually increased. Thus, soil restoration during the postagrogenic succession raised OM sequestration, increased microbial and enzymatic activities, which in turn contribute to soil health and delay of climate changes.