Bacteria diversity and microbial biomass in forest, pasture and fallow soils in the southwestern Amazon basin

Abstract

It is well-known that Amazon tropical forest soils contain high microbial biodiversity. However, anthropogenic actions of slash and burn, mainly for pasture establishment, induce profound changes in the well-balanced biogeochemical cycles. After a few years the grass yield usually declines, the pasture is abandoned and is transformed into a secondary vegetation called "capoeira" or fallow. The aim of this study was to examine how the clearing of Amazon rainforest for pasture affects: (1) the diversity of the Bacteria domain evaluated by Polymerase Chain Reaction and Denaturing Gradient Gel Electrophoresis (PCR-DGGE), (2) microbial biomass and some soil chemical properties (pH, moisture, P, K, Ca, Mg, Al, H + Al, and BS), and (3) the influence of environmental variables on the genetic structure of bacterial community. In the pasture soil, total carbon (C) was between 30 to 42 % higher than in the fallow, and almost 47 % higher than in the forest soil over a year. The same pattern was observed for N. Microbial biomass in the pasture was about 38 and 26 % higher than at fallow and forest sites, respectively, in the rainy season. DGGE profiling revealed a lower number of bands per area in the dry season, but differences in the structure of bacterial communities among sites were better defined than in the wet season. The bacterial DNA fingerprints in the forest were stronger related to Al content and the Cmic:Ctot and Nmic:Ntot ratios. For pasture and fallow sites, the structure of the Bacteria domain was more associated with pH, sum of bases, moisture, total C and N and the microbial biomass. In general microbial biomass in the soils was influenced by total C and N, which were associated with the Bacteria domain, since the bacterial community is a component and active fraction of the microbial biomass. Results show that the genetic composition of bacterial communities in Amazonian soils changed along the sequence forest-pasture-fallow.

Genetic and Functional Diversities of Microbial Communities in Amazonian Soils Under Different Land Uses and Cultivation

“…Only in Brazil the total area is 5.1 million km 2 (Fearnside, 2005). Despite its great beauty and exuberance, the Amazon rainforest is found in soils of low fertility, while its maintenance depends on the cycling of nutrients from vegetation covering (Cenciani et al, 2009). The quality and soil fertility are defined from the point of view of some essential attributes that maintain the agricultural productivity, namely as: soil ability to promote plant growth, water supply and nutrient processing, efficient gases exchange in the atmosphere-soil interface and the activity of micro and macro organisms (Dilly & Nannipieri, 2001).…”

“…In this context it is highlighted the role of soil microbial biomass (SMB), defined as the living portion of soil organic matter, excluding roots and larger organisms than, approximately, 5000 m 3 . The microbial biomass comprises the dormant and the metabolically active organisms in the soil; performing a primary role for maintenance and the products of microbial recycling are then absorbed by plant roots (Cenciani et al, 2009). Soil quality or even "soil health" can be analyzed by the activity of microbial biomass, one of few active fractions of organic matter, sensitive to tillage and that can be quantified.…”

“…The quality and soil fertility are defined from the point of view of some essential attributes that maintain the agricultural productivity, namely as: soil ability to promote plant growth, water supply and nutrient processing, efficient gases exchange in the atmosphere-soil interface and the activity of micro and macro organisms (Dilly & Nannipieri, 2001). In this context it is highlighted the role of soil microbial biomass (SMB), defined as the living portion of soil organic matter, excluding roots and larger organisms than, approximately, 5000 m 3 (Cenciani et al, 2009). In recent years many technological advances and the development of new and independent cultivation techniques led microbiologists to explore more precisely the "black box" of soil microbial diversity.…”

Land-use systems affect Archaeal community structure and functional diversity in western Amazon soils

“…In this context, Brazil has been slowing down deforestation by trying to make better use of already cleared land (Tollefson, 2010). However, the establishment of policies for the sustainable use of land in the Amazon region requires considering not only the diversity of flora and fauna but also the aspects of microbial ecology and biogeochemistry represented in this region as well (Piccolo et al, 1994;Borneman & Triplett, 1997;Moraes et al, 2002;Cenciani et al, 2009;Chaves et al, 2009;Jesus et al, 2009;O'Neill et al, 2009;Pazinato et al, 2010).…”

Early Changes in Soil Metabolic Diversity and Bacterial Community Structure in Sugarcane under Two Harvest Management Systems

“…Determination of significant shifts in the structure of the bacterial community, based on the profiles of 16S rRNA gene amplicons after denaturing gradient gel electrophoresis (PCR-DGGE), were observed in soils under forest, pasture, organic, and conventional management systems (Cookson et al, 2007;Liu et al, 2007;Cenciani et al, 2009;Rachid et al, 2012). …”