Distribuição das frações do carbono orgânico nos solos de florestas maduras na bacia Amazônica: o papel das propriedades do solo, da qualidade da liteira e do clima

Abstract

Soil organic carbon (SOC) stability is a function of environmental and biological conditions such as edaphic factors, climate and organic matter quality. Considering that a wide variation occurs in all these parameters across Amazonia, one could expect that there should be systematic variations in SOC fractions across the area. Understand the processes involved in carbon stabilization in tropical pristine forests is very important to improve our understanding of ecosystem function and to allow the preparation of better and more accurate models of soil carbon dynamics. We used soil carbon fractionation techniques to answer the following questions: (i) How the different soil carbon fractions are distributed among the different soil types, at varying depths (ii) How they are inter-related and (iii) What is the role of soil properties, climate and litter quality in modulating SOC fractions across the Amazon Basin. This study was carried out on 30 1 hectare pristine rainforest plots located at Brazil, Peru, Colombia and French Guyana. Our results show that SOC concentration in the different fractions vary following a soil weathering gradient, where soil carbon on young, more fertile soils is predominantly associated to relatively stable pools (silt+clay fraction) while highly weathered soils such as Ferralsols and Acrisols have large proportion of their soil carbon associated with stable aggregates. Very sandy and infertile soils have organic matter mainly associated with the maintenance of particulate organic matter on soil surface, which is clearly associated to poor organic matter quality and low decomposability. Concentration of SOC on most fractions was found to be mainly associated to edaphic properties, with the exception of the light fraction which is related to litter quality. We have found little evidence of climate influence on SOC fractions.