Abstract
Members of the phylum Acidobacteria are among the most abundant soil bacteria on Earth, but little is known about their response to environmental changes. We asked how the relative abundance and biogeographic patterning of this phylum and its subgroups responded to forest-to-pasture conversion in soils of the western Brazilian Amazon. Pyrosequencing of 16S rRNA genes was employed to assess the abundance and composition of the Acidobacteria community across 54 soil samples taken using a spatially nested sampling scheme at the landscape level. Numerically, Acidobacteria represented 20% of the total bacterial community in forest soils and 11% in pasture soils. Overall, 15 different Acidobacteria subgroups of the current 26 subgroups were detected, with Acidobacteria subgroups 1, 3, 5, and 6 accounting together for 87% of the total Acidobacteria community in forest soils and 75% in pasture soils. Concomitant with changes in soil chemistry after forest-to-pasture conversion—particularly an increase in properties linked to soil acidity and nutrient availability—we observed an increase in the relative abundances of Acidobacteria subgroups 4, 10, 17, and 18, and a decrease in the relative abundances of other Acidobacteria subgroups in pasture relative to forest soils. The composition of the total Acidobacteria community as well as the most abundant Acidobacteria subgroups (1, 3, 5, and 6) was significantly more similar in composition across space in pasture soils than in forest soils. These results suggest that preponderant responses of Acidobacteria subgroups, especially subgroups 1, 3, 4, 5, and 6, to forest-to-pasture conversion effects in soils could be used to define management-indicators of agricultural practices in the Amazon Basin. These acidobacterial responses are at least in part through alterations on acidity- and nutrient-related properties of the Amazon soils.
Highlights
Statistical comparison of soil chemical properties for forest and pasture soils indicated that forest conversion to pasture resulted in an increase in properties linked to soil acidity and nutrient availability in soil (Table S2)
The taxonomic analysis of the soil acidobacterial community was based on the retrieval of approximately 45,000 and 20,000 sequences of acidobacterial 16S rRNA gene fragments from forest soils and pasture soils, respectively (Table S3)
Significant differences between forest vs. pasture soils were found for the relative abundances of the Acidobacteria subgroups 2 (P < 0.005), 4 (P < 0.05), 7 (P < 0.0005), 10 (P < 0.05), 13 (P < 0.0005), (P < 0.0005) and (P < 0.005) (Table 1)
Summary
Land use change driven by human activities is considered the most important factor for biodiversity losses in the tropics (Sala et al, 2000) and a large number of studies have documented the negative effects of land use change for plants, animals (Gibson et al, 2011; Wearn et al, 2012), and most recently, microorganisms (Cenciani et al, 2009; Jesus et al, 2009; Navarrete et al, 2010, 2011, 2013, 2015; Taketani and Tsai, 2010; Rodrigues et al, 2013; Mirza et al, 2014; Mueller et al, 2014; Paula et al, 2014; Ranjan et al, 2015). Rodrigues et al (2013) reported that forest-to-pasture conversion resulted in a substantial decrease in the abundance of members of the bacterial phylum Acidobacteria. Acidobacteria are among the most common bacteria in soils worldwide, including in Amazon soils (Kim et al, 2007; Jesus et al, 2009; Navarrete et al, 2010, 2013, 2015). Greening et al (2015) proposed that consumption of trace gases such as H2 provides a dependable general mechanism for Acidobacteria to generate maintenance energy required for long-term survival in soils
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