Soil CO2 emission, microbial biomass, and microbial respiration of woody and grassy areas in Moscow (Russia)

Purpose: Urbanization significantly changes the carbon balance of the terrestrial ecosystem, an important component of which is soil CO2 emission. One of the main sources of soil CO2 emission is microbial decomposition of soil organic matter. In this regard, we hypothesized a relationship between soil CO2 emission and soil microbial properties (biomass, respiratory activity) in Moscow megapolis areas. Materials and methods: Soil CO2 emission was measured monthly (May–October) from the surface (or soil respiration, RS) and after the sequential removal of the two top 10-cm soil layers at woody (forest park, public garden) and grassy (grassland, arable) areas. Soil temperature (ST) and soil water content were recorded in 0–10-, 10–20-, and 20–30-cm layers, from which samples were taken to measure microbial biomass carbon (Cmic) and basal (microbial) respiration (BR). Results and discussion: RS ranged from 0.3 to 14.7 μmol СО2 m−2 s−1, with average values of 1.0, 5.4, 7.5, and 8.8 μmol СО2 m−2 s−1 for arable, forest park, public garden, and grassland, respectively. Removing the topsoil layer in woody areas resulted in higher CO2 release to the atmosphere than in grassy ones. Topsoil Cmic was on average 110, 331, 517, and 549 μg C g−1 and BR was 0.42, 0.87, 0.47, and 0.92 μg C-СО2 g−1 h−1 for arable, forest park, public garden, and grassland, respectively. Subsoil Cmic and BR were 1.5–3 times and 30–62% lower than in topsoil. RS in woody areas was more strongly dependent on ST than in grassy areas. Strong positive correlation between RS and topsoil Сmic and Corg (R2 = 0.98–0.99) was found. Conclusions: The RS of different Moscow’s areas might be predicted on the base of soil Cmic or Corg experimental data

Microbial C-availability and organic matter decomposition in urban soils of megapolis depend on functional zoning

Urbanization has various strong effects on soil processes. Despite an increasing number of studies focused on soil carbon (C) distribution and stocks within cities, the C and nutrient availability to microorganisms and their capacity to decompose organic matter remain nearly unknown. The factors responsible for these processes in megacities are characterized by a very high spatial heterogeneity and therefore, their effects should be investigated as related to specific environmental conditions – common for urban functional zones. This study focuses on the examination of the texture, C, available phosphorus (AP) and potassium (AK), mineral nitrogen, pH, and heavy metals (HMs) contents considering microbial C-availability (ratio of microbial biomass to C) and organic matter decomposition (BR) in soils of Moscow megapolis. The sampling sites were referred to recreational, residential and industrial zones. In the industrial and residential zones, the pH, AK, AP, and HMs were increased compared to recreational. Concurrently, the microbial С-availability and BR were much less in these zones. The high pH and AP content had negative effects on the BR for all soils. Soil segregation into groups (C-poor and C-rich, light texture and heavy texture) reduced heterogeneity and showed the additional patterns. In C-poor soils, the AP effect on BR was confirmed, but not of pH. The AK and Cu contents had negative effects on C-availability for C-poor and light soils, respectively. We conclude that careful control of the soil phosphorus and potassium contents as well as texture is necessary for planning the soil construction in megacities to consider their optimal functioning

Microbial Properties of Urban Soils With Different Land-Use History in New Moscow

Soil microbial properties are highly sensitive to present and past anthropogenic influences such as urban expansion, which is among the most drastic form of land-use change having substantial consequences for soils. New Moscow is an ambitious project to reduce the population of Moscow city that resulted in a rapid urbanization of former croplands, fallow lands, and forested areas. This study aimed to investigate the effects of historical land use in New Moscow on urban soil microbial properties. The land-use map of New Moscow from 2016 was compared with a similar map from 1981 to investigate the main urbanization pathways and land-use history of the new urbanized areas. Compared with 1981, the 2016 urban areas were more than three times greater, and the forest, pasture, and cropland areas were reduced by 9%, 87%, and 18%, respectively. Topsoil (0–10 cm) and subsoil (10–30 cm) samples were collected from 11 nonurbanized and 11 urbanized areas from current and former forest, pasture, and cropland soils. Soil microbial biomass carbon and respiration rates and chemical (pH and total C and N) and physical (bulk density and texture) properties were compared. Urban soils converted from forests and pastures showed negative effects of urbanization on topsoil microbial properties, whereas a conversion of cropland to urban soil increased microbial biomass carbon and microbial respiration. Soil microbial properties and N and C contents showed a strong correlation. The influence of historic land use on subsoil microbial properties was not significant

Carbon dioxide emission and soil microbial respiration activity of Chernozems under anthropogenic transformation of terrestrial ecosystems

The total soil CO2 emission (EM) and portion of microbial respiration were measured (in situ; May, June, July 2015) in Chernozems typical of virgin steppe, oak forest, bare fallow and urban ecosystems (Kursk region, Russia). In soil samples (upper 10 cm layer), the soil microbial biomass carbon (Cmic), basal respiration (BR) and fungi-to-bacteria ratio were determined and the specific microbial respiration (BR / Cmic = qCO2) was calculated. The EM was varied from 2.0 (fallow) to 23.2 (steppe) g СО2 m-2 d-1. The portion of microbial respiration in EM was reached in average 83, 51 and 60% for forest, steppe and urban, respectively. The soil Cmic and BR were decreased along a gradient of ecosystems transformation (by 4 and 2 times less, respectively), while the qCO2 of urban soil was higher (in average by 42%) compared to steppe, forest and fallow. In urban soil the Cmic portion in soil Сorg and Сfungi-to-Сorg ratio were by 2.6 and 2.4 times less than those for steppe. The relationship between microbial respiration and BR values in Chernozems of various ecosystems was significant (R2 = 0.57)

Assessing soil-like materials for ecosystem services provided by constructed technosols

Urbanization results to a wide spread of Technosols. Various materials are used for Tech-nosols’ construction with a limited attention to their ecosystem services or disservices. The research focuses on the integral assessment of soil-like materials used for Technosols’ construction in Moscow megalopolis from the ecosystem services’ perspective. Four groups of materials (valley peats, sediments, cultural layers, and commercial manufactured soil mixtures) were assessed based on the indicators, which are integral, informative, and cost-effective. Microbial respiration, C-availability, specific respiration, community level physiological profile, and Shannon’ diversity index in the materials were compared to the natural reference to assess and rank the ecosystem services and disser-vices. The assessment showed that sediments and low-peat mixtures (≤30% of peat in total volume) had a considerably higher capacity to provide C-sequestration, climate regulation and functional diversity services compared to peats and high-peat mixtures. Urban cultural layers provided ecosystem disservices due to pollution by potentially toxic elements and health risks from the pathogenic fungi. Mixtures comprising from the sediments with minor (≤30%) peat addition would have a high potential to increase C-sequestration and to enrich microbial functional diversity. Their implementation in urban landscaping will reduce management costs and increase sustainability of urban soils and ecosystem