Data_Sheet_1_Disturbance Size Can Be Compensated for by Spatial Fragmentation in Soil Microbial Ecosystems.PDF

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 toward 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.

土壤系统生态学的核心研究议题之一，是维持生态系统的功能。由于土壤会遭受不同空间构型的干扰，甄别出仍可维持生态系统功能的干扰特征，具备关键意义。在宏观生态学（macro-ecology）领域，破碎化对生态系统的影响始终存在学术争议，尤其是在景观尺度的灭绝阈值维度。该影响的正负性取决于所考量的破碎化类型：生境破碎化（habitat fragmentation）通常会加剧种群灭绝风险，而空间分布呈破碎状态的干扰事件，则在多数情形下会降低种群灭绝概率。本研究依托上述理论框架，剖析空间干扰特征如何决定微观尺度下的功能恢复力（functional resilience）。我们采用数值模型eColony，该模型覆盖细菌生长、底物消耗与扩散过程，用以分析作为典型核心微生物生态系统功能的生物降解作用，对干扰事件的动态响应。我们系统调控了干扰事件的发生频率，以及受干扰区域的规模与破碎化程度。研究发现，干扰规模对功能恢复的影响，取决于干扰的空间破碎化程度，这表明在一定范围内，干扰规模可通过受干扰区域的空间构型予以补偿。总体而言，生物降解性能会随受干扰区域规模扩大而下降，且随区域连通性提升而进一步降低。然而，若干扰呈现高度破碎化特征，则干扰规模的提升并不会对生物降解性能产生显著影响，除非干扰规模达到临界阈值。此时，生态系统功能性能会出现急剧下滑。在周期性重复干扰条件下，该临界干扰规模会随干扰频率升高向更低的数值偏移。本研究结果表明，空间干扰特征对土壤微生物生态系统的功能恢复力至关重要。干扰规模与破碎化程度的临界值，源自二者之间的相互作用。因此，在景观尺度上被广泛讨论的这些特征，在评估土壤生态系统功能恢复力时，同样需要在更小尺度上予以充分考量。