How Does Urban Development Affect Soil Microbial Community?

Microorganisms are essential members of soil ecosystems, and they form complex, interactive networks [4] including communications and interactions with each other that are similar to human communities. The soil microbial community contributes to global ecological stabilization by providing various terrestrial ecosystem services, such as nutrient cycling and degradation of pollutants [4]. Moreover, the soil microbial community is an important carbon storage source [1]. However, the soil microbial community can be easily affected by urban development. Here I review some common urban influences on soil microbes.

The influence of urban land use

The diversity of soil microbial community depends on various environmental factors, such as soil density, vegetation cover and moisture content [2]. However, urban development brings huge alterations in natural environmental conditions, directly or indirectly resulting in the decreasing diversity of urban soil microbial community compared to natural habitats. One main alteration is that the expansion of urban areas and the construction of urban facilities such as roads and buildings cause fragmentation of soil microbial habitats (Fig 1.) [3]. Moreover, plant-microbe interactions are also disrupted due to the loss of plant diversity during urbanization [4]. Compared with places away from urban areas or that have more plants—such as parks or urban forests—soil microbial diversity has been shown to be lower in more urbanized areas [4, 7].

Fig 1. Types of urban soil ecosystems [3]

Different types of land use also have huge impacts on the structure and the composition of soil microbial communities. For example, land hardening for urban facility construction transforms natural soil surfaces into impermeable surfaces that restricts the flow of oxygen, water and nutrients into soil [2]. This enclosed environment leads to the increase of anaerobic soil bacteria that release greenhouse gases such as methane [2].

The influence of urban pollution

Soil pollution in urban development involves industrial pollution, overuse of chemical pesticide or fertilizers, waste disposal and many other types. Here we will simply introduce the types of soil pollution mentioned above and their effects on soil microbes. Hydrocarbons spread from urban gas stations, and heavy metals such as lead, cadmium, cobalt, chromium and copper from industrial emissions are toxic pollutants to soil microbes [6]. Overuse of fertilizers containing nitrogen or phosphorus in soil can change the original soil nutrient cycle and disrupt the balance in soil ecosystems [9]. Landfill rubbish such as plastic waste may release harmful chemical compounds that disturb the physiological activities of soil microbes and decrease microbial diversity in soil [5]. What’s worse, some pollutants such as heavy metals accumulate in soil and organisms, causing continuous and increasing harm to soil biodiversity and other urban organisms [5].

Urban greening reduces the impact of urban development

Urban greening is one of the few measurements in urban development that effectively help preserve the natural habitats of soil microbes (Fig 2). The parks, gardens, and urban forests in cities have relatively abundant vegetation [7]. Plant root systems can regulate the chemical properties (e.g., pH) and physical properties (e.g., moisture levels and the size of soil particles) of soil, and enhance air exchange inside and outside the soil [8], creating diverse and dynamic living environments for soil microorganisms. Diverse plant species and vegetation types are essential factors to determine soil biodiversity [8], which are considerable points in an urban greening plan.

Fig 2. How plants affect soil microbial community [8]

Conclusion

Urban development significantly affected soil microbial community through land use and impervious surfaces, harmful pollutants, and soil nutrient changes. These alterations lead to a decline in soil microbial diversity and function. However, the protection of urban soil is easily ignored in urban development despite its importance for ecosystem health. We call for the attention from urban construction planners to realize the importance of soil microbial community in urban ecosystems and carbon cycle as well as enhance soil health conservation, ensuring healthy and functional soil microbial ecosystems in cities. The actions such as increasing urban green space to include diverse species will help reduce the negative impacts of urban development on soil microbial community diversity.

 

References

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2. Nugent, A., & Allison, S. D. (2022). A framework for soil microbial ecology in urban ecosystems. Ecosphere (Washington, D.C), 13(3). https://doi.org/10.1002/ecs2.3968
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