Soil properties and tree species drive ß-diversity of soil bacterial communities

Soil properties and tree species drive ß-diversity of soil bacterial communities

Soil Biology & Biochemistry 76 (2014) 201e209 Contents lists available at ScienceDirect Soil Biology & Biochemistry journal homepage: www.elsevier.c...

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Soil Biology & Biochemistry 76 (2014) 201e209

Contents lists available at ScienceDirect

Soil Biology & Biochemistry journal homepage: www.elsevier.com/locate/soilbio

Soil properties and tree species drive ß-diversity of soil bacterial communities William J. Landesman a, b, *, David M. Nelson a, Matthew C. Fitzpatrick a a b

University of Maryland Center for Environmental Science, Appalachian Laboratory, Frostburg, MD 21532, USA Green Mountain College, One Brennan Circle, Poultney, VT 05764, USA

a r t i c l e i n f o

a b s t r a c t

Article history: Received 17 February 2014 Received in revised form 25 April 2014 Accepted 17 May 2014 Available online 29 May 2014

A challenge in ecology and biogeography is to understand the drivers of the composition and distribution of biological communities. Environmental factors (especially pH) and dispersal limitation are thought to exert the primary controls on the composition of soil bacterial communities. However, quantifying their relative importance remains difficult because of analytical uncertainties. For example, the relationship between bacterial community composition and soil pH, which is often nonlinear, is typically evaluated with a linear test and without accounting for variability in rates of turnover along environmental gradients. Furthermore, potential drivers of variation in soil pH, and therefore bacterial community composition, are not commonly analyzed during microbial biogeographical studies. To address these issues we collected 700 soil samples across multiple spatial scales from beneath four late-successional tree species within 12 forests in the eastern United States. We performed high-throughput sequencing of 16S rDNA amplicons and measured soil properties thought to influence soil bacterial composition. Generalized Dissimilarity Modeling, a non-linear form of matrix regression, indicated that geographic distance and soil properties explained 77.3% of the deviance in turnover in overall bacterial community composition. However, only 2.1% of the explained deviance was attributable to geographic distance, indicating little contribution of dispersal limitation to bacterial ß-diversity across scales of ~1.7 m to >1000 km. Although 81.7% of the explained deviance in overall bacterial composition was attributable to soil properties, particularly soil pH, the magnitude and rate of compositional turnover varied among bacterial families across the pH gradient. The ß-diversity of three dominant families (Bradyrhizobiaceae, Hyphomicrobiaceae and Burkholderia) was explained by neither soil properties nor geographic distance. Differences in soil pH between certain tree species likely led to distinct bacterial communities at several sites. Thus, shifts in soil pH, potentially as the result of shifts in tree composition, will likely have important consequences for the composition of soil bacterial communities. © 2014 Elsevier Ltd. All rights reserved.

Keywords: Microbial ecology Generalized dissimilarity modeling Plantesoil interactions Bacteria Soil pH

1. Introduction A fundamental goal in microbial ecology is to understand the factors controlling variation in the composition and distribution of bacterial communities (e.g. Martiny et al., 2006; Ramette and Tiedje, 2007a; Hanson et al., 2012). Such information, in conjunction with knowledge of the functional characteristics of different taxa (e.g. Ferrier et al., 2007), is useful for projecting how environmental change may alter bacterially-mediated ecosystem processes (Wardle et al., 2004; Bardgett et al., 2008; van der Heijden

* Corresponding author. Green Mountain College, One Brennan Circle, Poultney, VT 05764, USA. Tel.: þ1 802 287 8323. E-mail address: [email protected] (W.J. Landesman). http://dx.doi.org/10.1016/j.soilbio.2014.05.025 0038-0717/© 2014 Elsevier Ltd. All rights reserved.

et al., 2008). Two conceptual frameworks have been used to explain the biogeography of bacterial communities. The first posits that the occurrence of bacteria is mainly a function of local environmental conditions, since microbes have largely unlimited dispersal potential and the ability to remain dormant until conditions become favorable for growth and reproduction (de Wit and Bouvier, 2006). The second argues that spatial processes, most notably dispersal limitation, are the primary constraint on community composition, because they exclude taxa from otherwise suitable environments (Ramette and Tiedje, 2007a). However, quantifying the relative importance of these hypotheses remains a challenge. High-throughput sequencing of 16S rDNA in environmental samples enables assessment of microbial b-diversity and thus investigation of environmental vs. spatial controls of bacterial

oak trees (Fig. 4), but individual soil samples from beneath these tree species that overlapped in NMDS space (Fig. S5) also shared similar pH values. At some sites (e.g. PS), the magnitude of the difference between the average pH of tree species was small (<0.25 pH units); consequently there was relatively poor separation of bacterial communities among samples (Fig. S5). Furthermore, many factors that are generally independent of tree species contribute to

soil acidity, including the composition of the soil parent material (Dijkstra and Smits, 2002), leaching of base cations via acid deposition (Likens et al., 1996; Warby et al., 2009), climate, soil texture and the contribution of neighboring trees and understory species (Binkley, 1995; Brady and Weil, 2008). These factors may contribute to the observed variability in the relationship between trees and soil pH across sites.