Department of Landscape Design and Sustainable Ecosystems, Agrarian‐ Technological Institute, RUDN University, Miklukho‐Maklaya str., 6, Moscow, Russia Department of Soil Science of Temperate Ecosystems, Department of Agricultural Soil Science, University of Göttingen, Büsgenweg 2, Göttingen, Germany Correspondence V. Vasenev, Department of Landscape Design and Sustainable Ecosystems, Agrarian‐ Technological Institute, RUDN University, Miklukho‐Maklaya str., 6, Moscow, Russia. Email: vasenyov@mail.ru Funding information DAAD‐Mikhail Lomonosov fellowship; Ministry Education and Science of the Russian Federation, Grant/Award Number: Agreement No 02.A03.21.0008; Russian Foundation for Basic Research, Grant/Award Number: 15‐34‐ 70003; Russian Science Foundation, Grant/ Award Number: 17‐77‐20046

Urban soils as hot spots of anthropogenic carbon accumulation: Review of stocks, mechanisms and driving factors

Projection of urban expansion and related changes in soil carbon stocks in the Moscow Region

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.

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Using constructed soils for green infrastructure – challenges and limitations

C-sequestration, as a function of soils, is known to help mitigate climate change. However, the potential of urban soils to be C-sinks or sources, is widely unknown. This study aims to understand the role and significance of urban soils in the C-balance of the region. It reveals several important findings about the C-balance capacities of urban soils and the multiple factors affecting this balance. This two-year study focused on soil organic carbon (SOC) stocks and CO 2 emissions of urban soils in the city of Kursk, located in the Central Chernozemic region of Russia, an area known to have some of the most fertile soils in the world. SOС stocks and emissions were studied in residential, recreational, and industrial functional zones and in comparison to corresponding natural reference soils to analyze the influence of urbanization on C turnover Urban soils were found to store 20 to 50 kg С m − 2 in 1.5 m layer; 10–30% less than in corresponding natural Luvic Chernozems and Chernic Phaeozems, but greater than what has been reported for many other cities. The urban soils with developed cultural layers stored more C in subsoil compared to the natural soils. Emissions of CO 2 in urban soils, however, were higher than from Chernic Phaeozems but comparable to those from Luvic Chernozems. The CO 2 /SOC stocks ratio in urban soils was two–three times higher than in natural soils. These outcomes point to the intensive C turnover and low sustainability of SOC stocks in urban soils. This study found evidence that the recent urbanization of the Chernozemic region has adversely affected the C balance. Natural soils in the region are important C sinks, however they can convert to C sources in result of urbanization.

Carbon stocks and CO2 emissions of urban and natural soils in Central Chernozemic region of Russia

A review of Russian and foreign approaches to analyze and assess the ecological and socioeconomic role of urban and technogenic soils is made in the context of the two popular concepts: the ecological functions of soils and ecosystem services. The modern definitions, classification, and evaluation of ecosystem services and their relationships with soil functions are considered both in general and in relation to urban and technogenic soils. Despite some methodological differences, the work shows that the concepts are closely related, and their joint use is highly promising. Three practical examples for the cities of Moscow, Hangzhou, and Hong Kong show a consistent transition from the analysis of soil properties and functions to the assessment of ecosystem services and decision making in engineering, urban improvement, and sustainable urban development.

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The Ecological Functions and Ecosystem Services of Urban and Technogenic Soils: from Theory to Practice (A Review)

Urbanization coincides with remarkable expansion of turf grasses and their increasing role in environmental processes and functions, including carbon (C) sequestration. Soil organic carbon (SOC) stocks in turf grass soils are substantial, however, an intensive soil respiration is also likely. Therefore C sequestration in turf grasses remains uncertain, especially at the early stages after development, when C uptake and CO2 emissions are unbalanced. We analyzed changes in SOC stocks and CO2 emissions at the experimental turf grasses in Moscow megapolis during the three years period after establishment. An influence of the three contrast depths of organic layers (5, 10 and 20 cm) on soil and biomass C and on the ornamental functions of turf grasses was studied. Total CO2 emission from the turf grasses during the observation period exceeded C uptake in grass and root biomass by two to three times. Therefore the turf grasses at the early stages of development are important source of biogenic C. Although the C losses were substantial, CO2 emission decreased and C uptake in biomass increased by the end of the observation period. The highest ratio of sequestered and emitted C was obtained for the thick turf grass soil constructions with a 20 cm organic layer. The highest ornamental value, indicated by the projective cover and sprout density, was also obtained for the thick turf grasses, which is essential to consider for developing the best management practices and sustainable turf grass soil constructions.

Changes of soil organic carbon stocks and CO2 emissions at the early stages of urban turf grasses’ development

Urbanization is a key land-use change pathway, increasing urban population and resulting in abandonment of rural areas. Urbanization alters profoundly soil properties and functions, including soil respiration [90]. Soil respiration includes heterotrophic (microbial) and autotrophic (root) components. Both are driven by biotic and abiotic factors. Soil respiration and its components in urban ecosystems remain poorly known. In the present study, the spatial and temporal variability of total soil respiration (Rs) and its components were analyzed for different ecosystems included in the Moscow megalopolis area. In particular, highly impacted areas of urban green lawns were compared to arable lands and urban forest sites. Respiration fluxes were monitored during the whole vegetation period. An average Rs was significantly higher for the most disturbed sites, compared to more natural sites. For all the sites, Rh was the dominant component of soil respiration. We report the highest heterotrophic respiration ratio to microbial C (qCO2 = Rh/Cmic) for the lawn land use, followed by arable sites and forest sites, characterized by the lowest qCO2. An average Ra contributed to total Rs only to a minor extent (26%) and increased in all study sites along the season. Ra absolute values and contribution to Rs were similar for different land use types.

Urban Soil Respiration and Its Autotrophic and Heterotrophic Components Compared to Adjacent Forest and Cropland Within the Moscow Megapolis

Urban soil respiration and its autotrophic and heterotrophic components compared to adjacent forest and cropland within the moscow megapolis

The eddy covariance (EC) technique as a powerful statistics-based method of measurement and calculation the vertical turbulent fluxes of greenhouses gases within atmospheric boundary layers provides the continuous, long-term flux information integrated at the ecosystem scale. An attractive way to compare the agricultural practices influences on GHG fluxes is to divide a crop area into subplots managed in different ways. The research has been carried out in the Precision Farming Experimental Field of the Russian Timiryazev State Agricultural University (RTSAU, Moscow) in 2013 under the support of RF Government grant # 11.G34.31.0079, EU grant # 603542 LUС4С (7FP) and RF Ministry of education and science grant # 14-120-14-4266-ScSh. Arable Umbric Albeluvisols have around 1% of SOC, 5.4 pH (KCl) and NPK medium-enhanced contents in sandy loam topsoil. The CO 2 flux seasonal monitoring has been done by two eddy covariance stations located at the distance of 108 m. The LI-COR instrumental equipment was the same for the both stations. The stations differ only by current crop version: barley or vetch and oats. At both sites, diurnal patterns of NEE among different months were very similar in shape but varied slightly in amplitude. NEE values were about zero during spring time. CO 2 fluxes have been intensified after crop emerging from values of 3 to 7 µmol/s∙m 2 for emission, and from 5 to 20 µmol/s∙m 2 for sink. Stabilization of the fluxes has come at achieving plants height of 10-12 cm. Average NEE was negative only in June and July. Maximum uptake was observed in June with average values about 8 µmol CO 2 m −2 s −1 . Although different kind of crops were planted on the fields A and B,  GPP dynamics was quite similar for both sites:  after reaching the peak values at the mid of June, GPP decreased from 4 to 0.5 g C CO 2 m -2 d -1 at the end of July. The difference in crops harvesting time that was equal two weeks did not significantly influence the daily GPP patterns. Cumulative assimilation of CO 2 at the end of the growing season was about 150 g C m −2 for both sites. So the difference in NEE was the consequence of essentially higher respiration rates in case of vetch and oats (about 350 g C m −2 ) comparing to barley (250 g C m −2 ) that needs additional research. The results have shown high daily and seasonal dynamic of CO 2 emission too as a result of different and contrasted conditions: crop type, crop development stage, soil moisture and air temperature. Obtained unique for Russian agriculture data are useful for land-use practices environmental assessment, for soil organic carbon dynamics analysis and agroecological evaluation.

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Ilya Mazirov

Papers

Changes of soil organic carbon stocks and CO2 emissions at the early stages of urban turf grasses’ development

Urban Soil Respiration and Its Autotrophic and Heterotrophic Components Compared to Adjacent Forest and Cropland Within the Moscow Megapolis

Urban soil respiration and its autotrophic and heterotrophic components compared to adjacent forest and cropland within the moscow megapolis

Central Russia agroecosystem monitoring with CO2 fluxes analysis by eddy covariance method

Carbon dioxide fluxes dynamics comparison in Moscow urban forest and adjacent urban areas