Transformation of iron forms during pedogenesis after tree uprooting in a natural beech-dominated forest
Abstract
Treethrow dynamics was revealed to be a key biomechanical effect of individual trees in soil formation in mountain temperate forests. The resulting pit-mound microtopography represents a specific pattern of microsites with a potential influence on the course of pedogenesis (Samonil et al., 2010a).
The aim of this study was to investigate the influence of tree uprooting on the transformation of Fe forms, as these forms indicate the degree of pedogenesis in Cambisols. Soil samples originated from a Haplic Cambisols region in a natural fir-beech forest in the Western Carpathians, Czech Republic.
Four pit-mound pairs of different ages - 20, 28, 180 and 191 years - as well as control, undisturbed profiles were sampled. Iron forms were studied using the following two different approaches: (i) Fe forms (exchangeable, crystalline, and amorphous together with organically complexed Fe) were extracted by three specific extracting agents then subsequently determined by ICP-OES; and (ii) non-destructive methods such as Voltammetry of Micropartides (VMP) and Diffuse Reflectance Spectroscopy (DRS) were used.
The following Fe species were detected by VMP within individual microsites: ionic Fe(III), ferrihydrite, and poorly crystalline and crystalline Fe(III) oxides. Mn(III,IV) oxides were also detected.
Goethite, hematite, Fe2+-Fe3+ pairs in Fe-bearing aluminosilicates (biotite, chlorite) and octahedral Fe3+ (total Fe3+ oxides and silicates) were quantified by means of the DRS technique. Ferrihydrite and Fe2+/Fe3+ ratio were higher in soils from the pits compared to samples originating from the mounds and this ratio increased with increasing depth.
Linear mixed effect (LME) models fitted by restricted maximum likelihood (REML) determined the relation between iron forms and other soil characteristics. Based on the development of Fe forms with time, we can conclude that tree uprooting significantly accelerates pedogenesis in the natural forest.