Interactive effects of urbanness and land cover types on soil carbon and nitrogen pools in green spaces.

Green spaces have potential to contribute substantially to carbon (C) capture and storage in urban environments. Yet, the impact of urbanisation and land cover change on key pools of C and nitrogen (N) in soils and soil organic matter (SOM) fractions is poorly resolved, which limits the ability to optimise management of urban environments. Here, we investigated the associations among urbanness and land cover change with C and N pools in bulk soil and SOM fractions in green spaces. Soils were sampled along an urbanness gradient from green spaces that contained three land cover classes (woodland, grassland and a transition area between each) across the metropolitan borough of Greater Manchester, northern England. We found that soil C and N concentrations in green space generally increased from rural to urban areas and from woodland to grassland. Plant species diversity plays a key role in connection between urbanness and soil C and N sequestration. We also found a significant interaction between land cover types and urbanness, which positively influenced soil C and N storage. Green space in the most urbanised areas contained higher mass percentage of particulate organic matter (POM) fractions compared to green space in the least urbanised areas, which indicated that urban soil is much more labile. However, the concentrations of C and N in these two fractions was also interactively mediated by the urbanness and land cover types. These findings demonstrate that urbanness and land cover types have significant effects on key pools of soil C and N and emphasise the importance of considering these pools for future urban planning and design amidst ongoing urbanisations to meet the target of carbon neutrality and sustainable living environment.