Urban greenspaces are fundamental for sustaining healthy and vibrant human populations, and, in many cases, represent the only point of contact citizens have with nature. Urban forests and lawns play critical roles in supporting biodiversity and ecosystem services that are at the core of the Sustainable Development Goals.
A better understanding of the environmental factors and management practices associated with these ecosystem functions and services is critical to ensure the sustainability of urban greenspaces. This is likely to become more crucial with an increase in the global human population and rising concerns of climate change.
Global surveys and experiments demonstrate that soil biodiversity can drive the multifunctionality of natural environments, however, much less is known, about the relationship of above- and below-ground biodiversity with ecosystem multifunctionality in urban greenspaces.
In a study published Nature Ecology and Evolution, a team of international scientists led by the Institute of Soil Science, Chinese Academy of Sciences and Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS) has published the results of the first standardized survey of urban greenspaces from 56 municipalities across six continents.
They investigated the relationship of plant and soil biodiversity with ecosystem functions, considering diverse community of microbes and multiple ecological functions, including multifunctionality, multiple individual functions, number of functions working over multiple thresholds, multiple dimensions of ecosystem functions, and key ecosystem services such as microbial-driven C pools, organic matter decomposition, plant productivity, nutrient cycling, water regulation, plant–soil mutualism, plant pathogen control, and antibiotic resistance regulation.
Here scientists found that soil biodiversity is positively correlated with multiple dimensions of ecosystem functions in urban greenspaces. In other words, urban greenspaces with greater soil biodiversity support higher levels of key groups of functions. Thus, conserving soil biodiversity is key to sustaining the multiple ecosystem functions provided by urban greenspaces. Specifically, the biodiversity of soil invertebrates was especially vital for supporting a high number of functions working at high levels of functioning in urban greenspaces.
The biodiversity of soil common taxa can be particularly important for ecosystem multifunctionality in urban greenspaces compared with that of rare taxa. “This result is commonly found when ecosystem functioning is determined by plant communities, just like Grime’s mass-ratio hypothesis. Soil common taxa that account for most biomass with high frequency of occurrence in urban greenspaces could competitively and efficiently utilize an array of resources, and occupy the highly dynamic and diverse environment.” says author Professor CHU Haiyan.
Unexpectedly, they also found that plant diversity had a limited capacity to influence ecosystem functions in urban greenspaces. “Plants in urban greenspaces are often non-indigenous species, have come from elsewhere, often a different continent, and have been selected for their horticultural value rather than their capacity to improve surface soils.” says senior author Dr Manuel Delgado-Baquerizo from the Instituto de Recursos Naturales y Agrobiología de Sevilla. “These introduced plants will be unlikely to have co-evolved with the soils and their microbial communities, or the climatic and environmental conditions (e.g., pollution, salinity, soil texture, water deficit) at a site, reducing their positive influence on ecosystem functions.”
Despite these limitations, Dr Manuel Delgado-Baquerizo also highlighted that “plant diversity is likely to be indispensable for other non-measured ecosystem services such as air purification, cooling, relaxation, and beautification, other than the basic ecosystem functions in natural ecosystems, and therefore, a fundamental component of urban greenspaces”.
Thus, conserving biodiversity (both soil biodiversity and plant diversity) in urban greenspaces is key to support the sustainability of urban ecosystems and human well-being.