Microbial Conversion

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Science  11 Jan 2013:
Vol. 339, Issue 6116, pp. 121
DOI: 10.1126/science.339.6116.121-a

Conversion of tropical forest to pasture has been widespread in the Amazon Basin in recent decades, a process that has been accompanied by a loss of diversity of flora and fauna and often by a reduction in soil fertility. However, how conversion affects soil microorganisms is largely unknown. Using DNA sequencing techniques, Rodrigues et al. compared the bacterial composition of forest and pasture soils at a site in Rondonia, Brazil. In pasture soils, there was a reduction in the diversity of taxa in the phylum Acidobacteria, organisms that are sensitive to increases in pH and soil carbon content, both of which occur after forest clearance. On the other hand, there was an increase in diversity within the phylum Firmicutes, which are tolerant of desiccation and greater extremes of temperature. At individual sample sites, the alpha diversity (number of taxa) of bacteria was higher in the pasture soils than in forest soils, but the beta diversity (variation between sites) of the pasture soils was significantly lower than in the forest. The lower beta diversity of the pasture soils implies a biotic homogenization of the soil microbiota after the conversion to pasture, and an eventual loss of overall diversity despite local increases in alpha diversity.

Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.1220608110 (2012).

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