Comparing podzolization under different bioclimatic conditions

Abstract

Silicate weathering and within soil redistribution of released metals are a near universal process believed to drive the formation of Podzols in various bioclimatic zones, ranging from tropical forest to Arctic environments. Yet the importance of climate and the fractionation of Al, Fe and Si in Podzols remains largely unknown. The aim of this study was to increase our understanding of climate-related variability in the podzolization mechanisms by conducting high-resolution chemical probing of seven soils in different bioclimatic zones and under different hydrological regimes: one well drained and one seasonally hydromorphic from the boreal zone (Sweden), two well-drained Podzols from a mild and humid area (NW Spain) and three, two poorly drained and one well drained soils, from the tropics (Brazil). The analytical strategy included seven selective dissolution techniques, in order to understand the distribution of Fe, Al and Si in organic (high, medium and low stability metal-OM complexes) and inorganic secondary compounds (short-range order and crystalline forms) in relation to their bioclimatic setting. Results indicate that the translocation of metals is coupled to the soil organic matter (SOM) mobilization in all three bioclimatic zones. The accumulation of metals and organic matter in the spodic horizons, in contrast, is contingent upon temperature, as well as on the local hydrological conditions and pH. Multivariate statistics allowed to identify the effect of climate, of soil hydrological conditions and of parent material in the soil vertical development. The high vertical resolution sampling and the extended fractionation employed were key for detecting the differences in Al, Fe and SOM dynamics in the studied soils, and revealed that different podzolization mechanisms are active in each bioclimatic zone.