Vegetation effects on pedogenetic forms of Fe, Al and Si and on clay minerals in soils in southern Switzerland and northern Italy

Abstract : The older forest type Quercetum–Betuletum (oak/birch; Q-type vegetation) in southern Switzerland and northern Italy was to a large extent replaced by chestnut forests (Castanea sativa; C-type vegetation) in roman times. When laurophylloid vegetation (L-type vegetation) invaded some of these chestnut systems during the last few decades, it caused detectable changes in organic chemistry. The invasion of the L-type vegetation was predominately due to increased winter temperatures. We tested whether these vegetation changes led to measurable long-term and short-term responses of the mineral matrix by comparing soils under Q-type with C-type vegetation (probing for long-term effects; > 100–2000 years) and soils under C-type with L-type vegetation (short-term effects; a few decades). To do so, we examined soil characteristics including the dithionite-, oxalate- and pyrophosphate-extractable forms of Fe, Al and Si as well as the phyllosilicate mineralogy of the clay fraction with a pair-wise comparison procedure. On L-type patches, short-term changes resulted in higher contents of secondary, poorly crystalline Fe. The accumulation of pedogenetic Fe probably results from a lower availability of organic complexing moieties under L-type vegetation and thus leading to a reduced removal. As soil acidity did not change with the vegetation types, a strong effect of organic compounds on Fe and Al chemistry must be assumed. A correlation analysis confirmed that metal binding to organic matter was different between L-type stands (correlation of Fe and Al with organic matter was less significant) and C-type stands. The differences in clay phyllosilicate assemblage between the different vegetation sites were rather small. There was, however, a trend towards higher contents of hydroxy-interlayered vermiculite (HIV) under L-type vegetation when compared to C-type sites. It seems that Al-polymers fixation in interlayers of 2:1 clay minerals was increased or their removal hindered at sites having L-type vegetation. Changes in the long-term (response to C-type vegetation) were only measurable for the pyrophosphate-extractable Si content (formation of phytolithe?). The colonisation of laurophyllous species led in the short-term to significant alterations of the soil system that were even more pronounced than the long-term effect of chestnut on soil quality.
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Remo Zanelli, Markus Egli, Aldo Mirabella, Daniele Giaccai, Mustapha Abdelmoula. Vegetation effects on pedogenetic forms of Fe, Al and Si and on clay minerals in soils in southern Switzerland and northern Italy. Geoderma, Elsevier, 2007, 141 (1-2), pp.119 - 129. ⟨10.1016/j.geoderma.2007.05.008⟩. ⟨hal-01848976⟩

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