Pedogenesis induced by Genista aetnensis (Biv.) DC. on basaltic pyroclastic deposits at different altitudes, Mt. Etna, Italy

Abstract

The paper deals with the role of Etnean broom [ Genista aetnensis (Biv.) DC.] on the early stages of pedogenesis on basaltic pyroclastic deposits (Mt. Etna, Italy) of different age and altitude previously not vegetated. After a few decades, this plant has been capable to arrest erosion and produce some soil features in both Entisols. The soil of Mts. Rossi, at a lower altitude, formed from a centenary parent material and hosted a broom plantation of about 50 years old. Here, the regimes of soil moisture ( ustic) and temperature ( mesic) limited the diffusion of the grass to the projection of the broom crowns, but favoured the diffusion of microorganisms and pedofauna. These conditions favoured a generalised alteration of the parent material and induced a certain horizon organisation. The soil of Mt. Vetore, at higher altitude, formed from a millenary parent material, and hosted a broom plantation of about 35 years old. At this site, the soil moisture ( udic) and temperature ( frigid) regimes favoured the formation of a thick and continuous carpet of gramineae. Yet, these conditions limited the activity of microorganisms and pedofauna, thus inducing a poorer horizon organisation. In this soil, because of the higher mean annual precipitation and root activity, most of the chemical modifications of the parent material occurred at the level of the rhizosphere, which acquired a thickness of 2–3 cm. From a chemical and mineralogical point of view, horizontal variations between rhizosphere and matrix were more evident than those among horizons. The most striking change occurring in the rhizosphere was the accumulation of secondary minerals such as oxalates and easily reducible Fe-oxyhydroxides. We also inferred that, in the environment of Mt. Etna, the excretion of oxalic acid from the roots of the broom could represent a strategy of nutrient uptake, in particular P, Mg and K.