Disturbance Promotes Non-Indigenous Bacterial Invasion in Soil Microcosms: Analysis of the Roles of Resource Availability and Community Structure

Abstract

BackgroundInvasion-biology is largely based on non-experimental observation of larger organisms. Here, we apply an experimental approach to the subject. By using microbial-based microcosm-experiments, invasion-biology can be placed on firmer experimental, and hence, less anecdotal ground. A better understanding of the mechanisms that govern invasion-success of bacteria in soil communities will provide knowledge on the factors that hinder successful establishment of bacteria artificially inoculated into soil, e.g. for remediation purposes. Further, it will yield valuable information on general principles of invasion biology in other domains of life.Methodology/Principal FindingsHere, we studied invasion and establishment success of GFP-tagged Pseudomonas fluorescens DSM 50090 in laboratory microcosms during a 42-day period. We used soil heating to create a disturbance gradient, and hypothesized that increased disturbance would facilitate invasion; our experiments confirmed this hypothesis. We suggest that the key factors associated with the heating disturbance that explain the enhanced invasion success are increased carbon substrate availability and reduced diversity, and thus, competition- and predation-release. In a second experiment we therefore separated the effects of increased carbon availability and decreased diversity. Here, we demonstrated that the effect of the indigenous soil community on bacterial invasion was stronger than that of resource availability. In particular, introduced bacteria established better in a long term perspective at lower diversity and predation pressure.ConclusionWe propose increased use of microbial systems, for experimental study of invasion scenarios. They offer a simple and cost-efficient way to study and understand biological invasion. Consequently such systems can help us to better predict the mechanisms controlling changes in stability of communities and ecosystems. This is becoming increasingly relevant since anthropogenic disturbance causes increasing global change, which promotes invasion. Moreover, a thorough understanding of factors controlling invasion and establishment of artificially amended micro-organisms will mean a major step forward for soil-remediation microbiology.

A conceptual framework for invasion in microbial communities

“…Disturbances tend to decrease community density and diversity, potentially increasing the available niche space -in other words temporarily decreasing competition. The invader establishment then depends on its ability to cover the available niche space of the disturbed community (Liu et al, 2012;De Roy et al, 2013).…”

“…Similarly, the absence or the constant supply of nutrients to the community during an invasion experiment might not simulate the native conditions of the community correctly. In fact, when nutrients are supplied in a dynamic manner, the outcome of the invasion can change (Liu et al, 2012;Mallon et al, 2015a). Overall, we suggest designing experiments that elucidate the role of dispersal, drift, and diversification, because these processes have received less attention.…”

Experimental evolution in fluctuating environments: tolerance measurements at constant temperatures incorrectly predict the ability to tolerate fluctuating temperatures

“…Most importantly, disturbed and heterogeneous environments have been shown to be more vulnerable to invasions than constant and uniform environments (Burke and Grime 1996, Davis et al 2000, Davies et al 2005, Melbourne et al 2007, Liu et al 2012. The significance of resource fluctuation promoting invasions is well known (Davis et al 2000, Li andStevens 2012).…”

Microbial Invasions: The Process, Patterns, and Mechanisms

“…process [15][16][17][18][19][20][21][22][23][24][25][26][27]. A synthesis of these recent conclusions and their eventual merging into existing ecological and microbiological theory will enhance our understanding of the fundamental processes that govern microbial life.…”