Urban soils and cultural layers may accumulate C over centuries and consequently large C stocks may be sequestered beneath cities. Processes and mechanisms leading to high C accumulation in urban soils remain unknown. Data on soil organic carbon (SOC), soil inorganic carbon (SIC), black (pyrogenic) carbon (BC), and nitrogen contents and stocks in urban soils were collected from 100 peer‐reviewed papers. The database (770 data points for SOC, SIC, and BC stocks from 116 cities worldwide) was analysed considering the effects of climate and urban‐specific factors (city size, age, and functional zoning) on C stocks. The processes of C accumulation specific for urban soils were analysed, and C sequestration rates were assessed. For the wide range of climatic conditions, total C content in urban soils was 1.5–3 times higher, and C accumulation was much deeper compared with natural soils, resulting in 3–5 times larger total C stocks. Urban SOC stocks increased with latitude, whereas SIC stocks were less affected by climate. City size and age were the main factors explaining intercity differences in C stocks. The intracity variability of C and N stocks was dominated by functional zoning: Large SOC and N stocks in residential areas and large SIC and BC stocks in industrial zones and roadsides were consistent across all climates and for cities of various sizes and ages. Substantial amounts of SOC, SIC, and N are sequestered in the subsoils, cultural layers, and sealed soils, underlining the importance of these hidden stocks for C assessments. Long‐term С input from outside the cities and associated C accumulation coincided with upward soil growth of ~50 cm per century, and continuous accumulation of 15–30 kg C/m2 per century in urban soils and cultural layers. We conclude that, despite the relatively small area of cities, urban soils are hot spots of long‐term soil C sequestration worldwide, and the importance of urban soils will increase in future with global urbanization.

Significant challenges of the COVID-19 pandemic highlighted that features of a modern, sustainable and resilient city should not only relate to fulfilling economic and social urban strategies, but also to functional urban design, in particular, related to urban blue and green infrastructure (BGI). Using results from a web-based questionnaire survey conducted May–July 2020 in Moscow (Russia) and Perth (Australia), this paper provides insights regarding citizens’ needs for and values of urban BGI as well as their changes during and after the COVID-19 restrictions. Survey data collected during the lockdown period have captured information about people’s ability to access green and blue spaces within urban BGI, inequalities in access, feelings, and values as well as needs and perceived pathways of future development of urban natural environment. In both cities, lockdowns limited access of people to green spaces which affected their mental and physical health. Survey results revealed that the quality, functionality, and location of open green spaces illustrated a disparity in distribution, meaning that in many cases several communities from particular neighborhoods suffered from limited access to BGI. Furthermore, in addition to analyzing perceptions and values of urban nature during the COVID-19 pandemic, some suggestions for improvement of urban BGI based on the survey responses are provided.

Abstract. With the rise in urban population comes a demand for solutions to offset environmental problems caused by urbanization. Green infrastructure (GI) refers to engineered features that provide multiecological functions in urban spaces. Soils are a fundamental component of GI, playing key roles in supporting plant growth, infiltration, and biological activities that contribute to the maintenance of air and water quality. However, urban soils are often physically, chemically, or biologically unsuitable for use in GI features. Constructed Technosols (CTs), consisting of mixtures of organic and mineral waste, are man-made soils designed to meet specific requirements and have great potential for use in GI. This review covers (1) current methods to create CTs adapted for various GI designs and (2) published examples in which CTs have been used in GI. We address the main steps for building CTs, the materials and which formulae should be used to design functional CTs, and the technical constraints of using CTs for applications in parks and square lawns, tree-lined streets, green buffer for storm water management, urban farming, and reclaimed derelict land. The analysis suggests that the composition and structure of CTs should and can be adapted to available wastes and by-products and to future land use and environmental conditions. CTs have a high potential to provide multiple soil functions in diverse situations and to contribute to greening efforts in cities (and beyond) across the world.