Short-term dynamics of C stocks and fluxes in constructed Technosols under green lawns along the bioclimatic gradient

The contribution of constructed Technosols to the C balance is still poorly understood since high C stocks in topsoil and biomass coincide with intensive CO₂ emissions. Moreover, geographical location can have an impact on C stocks and fluxes from Technosols, distinguishing hydrothermal regimes and specific substrates used for Technosols constructions in different regions. This study aims to study C stocks and fluxes in urban lawns on Technosols constructed in three cities in European Russia, following the bioclimatic gradient: Apatity (subarctic climate, north taiga) – Moscow (temperate climate, south taiga and mixed forests) – Rostov-on-Don (semi-arid climate, dry steppes). In each city, Technosols were constructed on summer 2020 to investigate dynamics in C stocks and fluxes at the very early stages after development, when the ecosystems are the most unstable. Both universal (constructed from similar materials and following the same technology) and regional-specific (different in substrates and the sequence of layers) Technosols were observed from September 2020 to April 2021. Soil C stocks were measured in the initial substrates (prior constructing) as well as in constructed Technosols after 2 months after construction. Dynamics in aboveground biomass was measured during the second half of the 2020 growing season (which duration differed between the regions considerably) and the length of the roots was measured at each of the cities once at the end of the 2020 growing season. Dynamics of CO₂ was monitored by IRGA once in two weeks during the growing season and once a month during the winter period (in Moscow the chamber approach with GC ending was used instead of IRGA in winter, whereas in Apatity both approaches were measured in parallel). Continuous measurements of the soil temperature were performed by iButtons with a 6-hour frequency.

The average air temperature in Rostov-on-Don was 4ºC higher than in Moscow and more than 10ºC higher than in Apatity, which generally follows the multiannual trends. The similar patterns were observed for the topsoil temperatures however the dynamics was smoother, especially in subsoil during the wintertime. The average CO₂ emission were in good coherence with soil temperatures: 0.25, 0.15 and 0.07 gC m^-2 hour^-1 were obtained in Rostov-on-Don, Moscow and Apatity respectively. Although the full seasonal biomass observation was not complete, preliminary the highest aboveground biomass was obtained in Apatity and the highest root biomass – in Rostov-on-Don. Overall lawn quality estimated based on the projected cover and shoot density was high and confirms that high-quality lawns can be grown almost regardless the bioclimatic conditions.

Acknowledgements The experimental research of C stocks and fluxes was performed with the support of Russian Science Foundation project № 17-77-20046. The climatic monitoring was carried out with the support of Russian Foundation for Basic Research project № 19-29-05187.