The microbiome of Amazonian dark earth: structure and function of the microbial communities from rhizosphere and biochar associated to the biogeochemical cycles

Abstract

In many tropical forests, turnover of organic material occurs rapidly and near to the soil surface, leading to a rapid loss of soil organic matter when forests are burned and land is used for agriculture. The organic matter fluxes in soil are a dynamic interaction of chemical and physical factors that affect biological processes. The anthropogenic addition of organic amendments including plant and animal material, pottery, and charcoal, into extant soil formed what are known as Terra Preta do Índio or Anthropogenic Dark Earth (ADE), which are prized by farmers for their sustained fertility, in regions where chronic soil infertility has lead, in part, to on-going destruction of primary forest to create marginal cropland. In ADE, the higher fertility at greater soil depth appears to be stabilized by the presence of black carbon (BC) and leads to large and diverse microbial populations. Understanding the biogeochemical processes involved in maintaining of fertility of ADE soils may lead to new technologies for soil management in the tropics, and provide a novel strategy for mitigating atmospheric CO2 by sequestering BC in soils, which may also serve as a nucleus for improved soil fertility. In addition, the understanding the functional diversity associated with organic matter degradation in ADE, and soil in general, may pose as much of a challenge to understanding soil microbial processes as trying to describe the actual taxonomic diversity. Measuring the microbial communities associated and their roles and contribution to biogeochemical processes of C and N cycles associated to the soil black carbon and also to the rhizosphere will illuminate how ADE has retained stable fertility for hundreds to thousands of years. The effect of rhizosphere will be considered in order to identify which microorganisms are carrying out a specific set of metabolic processes in the environment, until recently the usual way was to cultivate microbial strains in the laboratory, using growth media that contained a specific substrate, and then to identify the cultivated bacteria at the physiological, biochemical and, more recently, molecular levels. Or of our main goals will be attached to investigate and promote studies on cultivation of C-aromatic biodegraders, under aerobic and anaerobic growth, conditions. (AU)