The impact of pine self-afforestation on podzolization process in semi-natural grassland areas of Volyn Polissya (Ukraine)

Abstract

Background. Several theories have been proposed to explain the podzolization process. Currently, the role of organic matter in both weathering and immobilization in the illuvial horizon is clearly stated. The origin of soil organic matter and, accordingly, the various mechanisms of its influence on the soil material, create the basis of these theories. We assume that in the base-poor sandy soils under rich herbaceous vegetation with a well developed sod layer, the process of podzolization may also depend on CO2 soil formation agent . Materials and Methods. Four localities along a Pinus sylvestris L. self-afforestation chronosequence with pine stands of 10, 20, 40 yrs and an adjacent semi-natural grassland area were investigated in order to determine the patterns of podzolization process on sandy glacial till deposits. Soil pH, exchangeable base, soil cation exchange capacity, total content of soil organic carbon, amorphous Fe, Si and Al and total contents of Al, Fe, Mn, Zn, Cd, Pb, Cu, Co, Ni, Na, K were determined. Statistical analysis of the results was performed using LibreOffice for Linux. Results. During the pine succession, a previously well differentiated into horizons podzolic soil under the grassland vegetation community gradually degrades. Previously well-defined albic and spodic diagnostic horizons disappear, the soil profile becomes more acidic, the soil organic carbon, the base cation content and the base cation saturation decrease, the leaching rate of aluminium and iron increases. Secondary podzolization features in the soil profiles were detected 40 years after the onset of afforestation. The podzolization has not been intensive enough to develop fully fledged albic and spodic diagnostic horizons over such a short period. Conclusions. Based on the obtained soil morphological, physical and chemical properties, three most important agents of podzolization are proposed as principal for the studied area. The main gent under pine forest is fulvic acids that are produced during coniferous litter decomposition. Low molecular weight organic acids and carbon dioxide produced to the rhizosphere by roots and a root associated microbiota are mainly involved in the podzolization process under the grassland ecosystem.