Patterns in species persistence and biomass production in soil microcosms recovering from a disturbance reject a neutral hypothesis for bacterial community assembly.

Fen-Guo Zhang,Quan-Guo Zhang,Zhili He

doi:10.1371/journal.pone.0126962

Fen-Guo Zhang, Quan-Guo Zhang + Show 1 more

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https://doi.org/10.1371/journal.pone.0126962

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Journal: PloS one	Publication Date: May 11, 2015
Citations: 42	License type: CC BY 4.0

Affiliation: Beijing Normal University

Abstract

The neutral theory of biodiversity has emerged as a major null hypothesis in community ecology. The neutral theory may sufficiently well explain the structuring of microbial communities as the extremely high microbial diversity has led to an expectation of high ecological equivalence among species. To address this possibility, we worked with microcosms of two soils; the microcosms were either exposed, or not, to a dilution disturbance which reduces community sizes and removes some very rare species. After incubation for recovery, changes in bacterial species composition in microcosms compared with the source soils were assessed by pyrosequencing of bacterial 16S rRNA genes. Our assays could detect species with a proportional abundance ≥ 0.0001 in each community, and changes in the abundances of these species should have occurred during the recovery growth, but not be caused by the disturbance per se. The undisturbed microcosms showed slight changes in bacterial species diversity and composition, with a small number of initially low-abundance species going extinct. In microcosms recovering from the disturbance, however, species diversity decreased dramatically (by > 50%); and in most cases there was not a positive relationship between species initial abundance and their chance of persistence. Furthermore, a positive relationship between species richness and community biomass was observed in microcosms of one soil, but not in those of the other soil. The results are not consistent with a neutral hypothesis that predicts a positive abundance-persistence relationship and a null effect of diversity on ecosystem functioning. Adaptation mechanisms, in particular those associated with species interactions including facilitation and predation, may provide better explanations.

Highlights

A major advance in ecology in the past several decades is the development of the neutral theory of biodiversity [1,2,3]
One sample was frozen at -80°C, one sample was stored at 4°C and later used for preparing soil suspension, and the remaining was divided into 25 microcosms of 100 g in 250 mL Schott Duran bottles
The microcosms exposed to, and recovered from, the dilution disturbance showed dramatic decreases in the diversity indices compared with the source soils; and the extent of the decrease became larger with increasing magnitude of dilution disturbance (Fig 1)

Summary

Introduction

A major advance in ecology in the past several decades is the development of the neutral theory of biodiversity [1,2,3]. High functional equivalence among microbes is expected: a large number of microbial taxa may be replaceable in terms of their ecological effects on interacting species or ecosystem processes [13,14,15,16]. This can lead to two specific hypotheses: (i) the structure of microbial communities is largely governed by drift effects in ecological processes including extinction, recruitment, immigration and speciation [2,4,5,9,10] and (ii) decline of microbial diversity does not impair ecosystem functions [2,12,17,18]. Microcosm experiments that simulated microbial species loss have found both positive [20,21] and neutral effects [14,22] of diversity on ecosystem functions

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