Organic Matter Fractionation and Micromorphology From Soils of Trindade Island, South Atlantic

Abstract

This study characterized the soil organic matter (SOM) of Trindade Island from its humic fractions and micromorphological organization, recognizing the influence of environmental aspects on the distribution of these fractions. Eight soil profiles, representative of the different classes (Neosols, Cambisols and Organosols), associated to three parent materials (alkaline, basic rocks and carbonate sediments) and different topographic positions were analyzed. The fractionation of the humic substances and the C / N ratio were analyzed in all horizons. A surface horizon of each class was selected for micromorphological characterization in thin sections. Humina constituted the predominant fraction in the composition of the MOS of the Trindade soils. The highest concentrations occur in soils located in the highest, humid areas, and under larger vegetation. The majority accumulation of the humina fraction is due to the limited or low transformation of MOS, in turn associated with low macro and mesofauna activity. It is a humina inherited directly from the little transformed material. Other aspects such as texture, vegetal cover, pedoclimate explain the greater or lesser accumulation, and contribute to explain the differences between the profiles. The predominant humina fraction emphasizes the low mobility of MOS in the superficial horizons. However, profiles of the high areas presented indicative of incipient podzolization, concentrating AF and AH in depth. The study contributes with a first approximation in the characterization of Trindade MOS, important for the understanding of the carbon dynamics in the soil and fundamental for the environmental recovery of the Island.