Disturbance Size Can Be Compensated for by Spatial Fragmentation in Soil Microbial Ecosystems

Sara König,Thomas Banitz,Merlin C Köhnke,Martin Thullner,Florian Centler,Karin Frank,Anouk-Letizia Firle

doi:10.3389/fevo.2019.00290

Abstract

One major interest in soil systems ecology is to maintain ecosystem functions. As soil is exposed to disturbances of different spatial configurations, identifying disturbance characteristics that still allow for maintaining functions is crucial. In macro-ecology, the influence of fragmentation on ecosystems is continuously debated, especially in terms of extinction thresholds on the landscape scale. Whether this influence is positive or negative depends on the considered type of fragmentation: habitat fragmentation often promotes population extinction, whereas spatially fragmented disturbances reduce extinction probability in many cases. In this study, we make use of these concepts to analyze how spatial disturbance characteristics determine functional resilience on the microscale. We used the numerical model eColony considering bacterial growth, substrate consumption and dispersal for analyzing the dynamic response of biodegradation as an exemplary important microbial ecosystem function to disturbance events. We systematically varied the frequency of the disturbance events, and the size and fragmentation of the disturbed area. We found that the influence of the disturbance size on functional recovery depends on the spatial fragmentation of the disturbance, indicating that to some extent disturbance size can be compensated for by the spatial configuration of the disturbed area. In general, biodegradation performance decreases as the disturbed area increases in size and becomes more contiguous. However, if a disturbance is highly fragmented, an increase in disturbance size has no influence on biodegradation performance unless the disturbance is critically large. In this case, the functional performance decreases dramatically. Under recurrent disturbances, this critical disturbance size is shifted towards lower values depending on the disturbance frequency. Our results indicate the importance of spatial disturbance characteristics for functional resilience of soil microbial ecosystems. Critical values for disturbance size and degree of fragmentation emerge from an interplay between both characteristics. Consequently, these characteristics which are widely discussed on the landscape scale need to be equally considered on smaller scales when assessing functional resilience of soil ecosystems.

Highlights

Soil ecosystems are complex and exhibit a high spatial heterogeneity, for instance due to soil particles of different sizes resulting in a specific pore size distribution (Bartoli et al, 1991; Paz Ferreiro and Vidal Vázquez, 2010)
Our study indicates that functional resilience of microbial ecosystems in soil in terms of biodegradation performance depends on the spatial characteristics of the disturbance regime
The mean distance between disturbed und undisturbed habitats turned out to be a critical factor for recovery dynamics

Summary

Introduction

Soil ecosystems are complex and exhibit a high spatial heterogeneity, for instance due to soil particles of different sizes resulting in a specific pore size distribution (Bartoli et al, 1991; Paz Ferreiro and Vidal Vázquez, 2010). Disturbance events such as drought events or the release of toxic chemicals are often modulated by this soil texture. For determining the impact of disturbance events in soil ecosystems; we need to explicitly consider the spatial characteristics of such events This is especially important for understanding key factors that stabilize soil ecosystem functions. This ability is called “functional resilience” (Biggs et al, 2012), and can be further classified into “functional recovery” (i.e., the ability to recover a function after a disturbance), and “functional resistance” (i.e., the ability to stay essentially unchanged despite disturbances; Grimm and Wissel, 1997)

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