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The partitioning of mobile fractions of chemical elements in the mineral loamy soils during natural regeneration after plowing in Western Russia
Natural regeneration of forest soils affected by agricultural practices is a common phenomenon in many regions worldwide, particularly in boreal ecosystems. Affecting soil quality, the partitioning of extractable fractions of heavy metals and metalloids (HMMs) is not studied during natural regeneration. The following stages of natural regeneration after plowing have been identified in the Smolenskoye Poozerye National Park: agrocenosis, meadows, forests with the age of the tree stand <30, 35–60, 70–80, 80–110, 90–130, 110–135 years. In Retisols, the differentiation of following proxies was studied: pH, total organic carbon (TOC), grain size fractions, C:N, available P and K, easily-exchangeable, hardly-exchangeable, bound with complexes, Fe-Mn (hydr)oxides fractions of 27 chemical elements. Significant (p < 0.05) changes in soil proxies were found mainly in the umbric horizon, to a lesser extent in the albic horizon. During natural regeneration, the main factors of HMM partitioning in soils were relatively short-term (up to several decades) changes in acidity, content of TOC, available K and P. In the umbric horizon at the late stages of regeneration, an increase in the TOC content contributed to the accumulation of easily-exchangeable fractions of Fe, Mn, P, S, hardly-exchangeable fractions of Mn, Pb, Zn, bound with complexes Cd, Co, Mn, Pb and bound with Fe-Mn (hydr)oxides Pb. After land abandonment, a decrease in pH value provoked the decrease in the concentrations of the easily exchangeable fractions of Ca, K, Mg, Sr, as well as bound with complexes Be, K, Mg, P, Si, Sr, Y, and Zr from umbric horizon. At the late stages of regeneration, leaching of available K and P from the albic horizon is accompanied by a decrease in the concentration of trace elements, which indicates the natural regeneration of the soil proxies during the formation of mixed forests. Stadiality as an integral discrete characteristic of the observed changes in ecosystems is a secondary factor controlling partitioning of chemical elements.