Abstract
The objective of this work was to evaluate the catabolic gene diversity for the bacterial degradation of aromatic hydrocarbons in anthropogenic dark earth of Amazonia (ADE) and their biochar (BC). Functional diversity analyses in ADE soils can provide information on how adaptive microorganisms may influence the fertility of soils and what is their involvement in biogeochemical cycles. For this, clone libraries containing the gene encoding for the alpha subunit of aromatic ring-hydroxylating dioxygenases (α-ARHD bacterial gene) were constructed, totaling 800 clones. These libraries were prepared from samples of an ADE soil under two different land uses, located at the Caldeirão Experimental Station - secondary forest (SF) and agriculture (AG) -, and the biochar (SF_BC and AG_BC, respectively). Heterogeneity estimates indicated greater diversity in BC libraries; and Venn diagrams showed more unique operational protein clusters (OPC) in the SF_BC library than the ADE soil, which indicates that specific metabolic processes may occur in biochar. Phylogenetic analysis showed unidentified dioxygenases in ADE soils. Libraries containing functional gene encoding for the alpha subunit of the aromatic ring-hydroxylating dioxygenases (ARHD) gene from biochar show higher diversity indices than those of ADE under secondary forest and agriculture.
Highlights
The Anthrosols associated with pre-Colombian settlements in the Amazonian region are examples of how anthropogenic activities can promote the metabolic diversity of microbial populations in soil
High values were noted for P, cation exchange capacity (CEC) and soil organic matter (Table 1)
The high-CEC values were mainly due to organic matter content whose property of organic carbon is specific to soils with a high content of biochar, such as ADE soils
Summary
The Anthrosols associated with pre-Colombian settlements in the Amazonian region are examples of how anthropogenic activities can promote the metabolic diversity of microbial populations in soil. Anthrosols contain large pools of stable soil organic matter and are highly fertile. These soils, known as the anthropogenic dark earth of Amazonia (ADE) or “terra preta de índio”, Pesq. Content of charred biomass of unknown organic origin or pyrogenic black carbon, referred in the present study as biochar (BC), is 70 times higher in ADE, in comparison to their adjacent infertile soils (ADJ) without a past history of anthropogenic activities (Glaser, 2007). Biochar is the major structural distinction between the “terra preta de índio” and the adjacent soils and constitutes an important fraction of many soils worldwide, playing an important role in global carbon biogeochemistry (Liang et al, 2010). Because of its highly aromatic structure, biochar is chemically and biologically stable and remains in the environment for thousands of years
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