Urban parks and residential green spaces are home to higher, but also much more homogenous soil biodiversity than nearby natural forests and farmlands which could make the belowground world in cities less resilient to climate change, according to a new study.
"The findings show that we may have underestimated the impact of urbanization on soil biodiversity," says Scott Chang, a professor in the University of Alberta Faculty of Agricultural, Life & Environmental Sciences and co-author of the research, published in Nature Cities.
"We didn't expect it to have profound homogenization in soil microbial populations in urban green spaces across an entire continent. Those findings have implications for the impact of urbanization on ecosystem functions and services."
(Photo: John Ulan)
In an analysis of more than 200 soil samples from 13 Chinese cities across different climate regions, a team of international researchers compared microbial communities across four land-use types: forests, farmlands, urban parks and residential green spaces in the cities.
The results showed that city parks and residential areas consistently had a greater variety of bacteria, fungi and other tiny organisms called protists living in the soil than nearby forests or farmlands. For example, compared with forests, the number of species of those organisms in a sample increased by 14 to 17 per cent in urban parks. In residential areas, the diversity of bacteria and protists was 15 and 20 per cent higher, respectively.
This elevated richness was linked to higher pH levels in soil, likely due to urban management practices such as liming and fertilization, which create more favourable growing conditions for diverse species of fungi and bacteria.
However, the study also showed that while these urban soil communities were very diverse locally, they became about 13 per cent more alike, or homogenous, across the different cities, compared with nearby forests.
That loss of ecological uniqueness in urban soils across cities at larger scales leaves them more vulnerable to environmental stresses such as extreme weather, Chang says.
"There is a risk for those otherwise locally diverse microbial communities to respond to large-scale environmental changes all in a similar way, and as a result, ecosystem resilience could be lowered."
The findings can shape more effective urban planning and soil management to better protect both local and large-scale microbial diversity and function, through measures such as creating and stocking parks with diverse plant species, aerating the soil and applying liming materials like biochar, which promotes soil health.
Chang is also working with researchers at the University of Toronto, Université Laval and Concordia University to evaluate how applying biochar to urban green spaces in Canada might affect soil properties, including microbial diversity and functions such as the mitigation of greenhouse gas emissions.
As urbanization continues to intensify globally, understanding its impact on soil communities becomes increasingly important for maintaining environmental sustainability, says Chang, noting that future research needs to explore how these biodiversity changes could affect vital ecosystem services such as carbon sequestration.
"If microbial populations in urban soils across large scales are less vulnerable and more resilient to environmental changes, the services that they provide to society could be less negatively affected."
The study was a collaborative effort among researchers from China, Australia, Germany, Russia, Spain and the United Kingdom.
