The Relation Between Biological Activity of the Rain Forest and Mineral Composition of Soils

Abstract

In most soils of the humid tropics, kaolinitic topsoil horizons overlie more gibbsitic horizons. This arrangement cannot be produced simply by leaching. Quantitative measurement of the turnover of chemical elements in the litterfall in an Amazonian ecosystem indicates that the forest cycles a significant amount of elements, particularly silicon. As a result, fluids that percolate through topsoil horizons already contain dissolved silicon. This effect keeps silicon from being leached down and may account for the stability of kaolinite in the soil upper horizons. The soil mineral composition is thus maintained by biological activity.

Biogenic silica in tidal freshwater marsh sediments and vegetation (Schelde estuary, Belgium)

“…The BSi stocks in the aboveground P. australis vegetation were comparable to those found in an Amazon rain forest (83.4 g BSi m -2 ) (Lucas et al 1993), while the BSi in the upper 30 cm of sediment was comparable to the phytolith content of the soil of an equatorial rain forest in the Congo (1124 g m -2…”

Atributos químicos, físico-hídricos e mineralogia da fração argila em solos do Baixo Amazonas: Serra de Parintins

“…Latossolos cauliníticos são normalmente mais microagregados, com as partículas granulares menos arredondadas e mais parecidas com blocos (Schaefer, 1996), conforme observado neste estudo. Para Lucas et al (1993), o predomínio de caulinita sobre gibbsita em solos da Amazônia deve-se a intensa reciclagem de silício pela vegetação florestal, favorecendo a estabilidade da caulinita, mesmo em ambiente altamente intemperizado.…”

Genesis of Soils from Bauxite in Southeastern Brazil: Resilication as a Soil-Forming Process

“…Although some authors interpret the origin of these soil horizons as simultaneous to the formation of the bauxite, most understand that these horizons are the result of the geochemical degradation of bauxite from the growth of dense vegetation cover (Lucas et al, 1993). In this perspective, pedogenesis occurred on material that was already quite weathered, and not directly on fresh rock.…”