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

Temperature Sensitivity of Topsoil Organic Matter Decomposition Does Not Depend on Vegetation Types in Mountains

Rising air temperatures caused by global warming affects microbial decomposition rate of soil organic matter (SOM). The temperature sensitivity of SOM decomposition (Q(10)) may depend on SOM quality determined by vegetation type. In this study, we selected a long transect (3.6 km) across the five ecosystems and short transects (0.1 km) from grazed and ungrazed meadows to forests in the Northwest Caucasus to consider different patterns in Q(10) changes at shift of the vegetation belts. It is hypothesized that Q(10) will increase along altitudinal gradient in line with recalcitrance of SOM according to kinetics-based theory. The indicators of SOM quality (BR:C, respiration per unit of soil C; MBC:C, ratio of microbial biomass carbon to soil carbon; soil C:N ratio) were used for checking the hypothesis. It was shown that Q(10) did not differ across vegetation types within long and short transects, regardless differences in projective cover (14-99%) and vegetation species richness (6-12 units per plot). However, Q(10) value differed between the long and short transects by almost two times (on average 2.4 vs. 1.4). Such a difference was explained by environmental characteristics linked with terrain position (slope steepness, microclimate, and land forms). The Q(10) changes across studied slopes were driven by BR:C for meadows (R-2 = 0.64; negative relationship) and pH value for forests (R-2 = 0.80; positive relationship). Thus, proxy of SOM quality explained Q(10) variability only across mountain meadows, whereas for forests, soil acidity was the main driver of microbial activity

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