The effect of urbanisation on wintertime soil respiration in the Russian Arctic

Samenvatting

Purpose: With ongoing global warming, the carbon (C) balance of Arctic ecosystems has become a ‘hot’ topic; however, C stocks and fluxes in the soil of Arctic cities remain overlooked. The research aimed to estimate wintertime soil respiration and its contribution to the cumulative annual CO₂ emission from urban and natural soil of Apatity town in the Russian Arctic zone. Materials and methods: Soil respiration and microclimatic parameters (i.e., air temperature, soil temperature at 0 cm, 7 cm and 20 cm, and snow height) were observed from November 2020 until May 2023 at two urban (UR) sites (UR1 was in the town centre, and UR2 was in the town’s outskirts) in comparison to the natural forested area. Soil chemical (i.e., bulk density, pH_w, contents of available P, total C, N, bulk contents of Cu and Ni) and microbial (i.e., C_mic, BR, qCO₂, number of rRNA gene copies and community-level physiological profile) properties were analysed to explain patterns in soil respiration. Results: A thicker snow layer and warmer soil temperature at the urban sites determined a higher than at the natural site cumulative annual soil CO₂ efflux. The wintertime and snowy-period respiration accounted for 20% and 50% of the cumulative annual soil CO₂ efflux, respectively, with remarkable spikes during the thawing period. The high variation in soil respiration between urban sites was explained by different states of microbial communities, with higher activity shown for younger and more intensively managed soil at the UR2 site. Conclusion: An adequate estimate of soil C balance in Arctic cities must consider the wintertime soil respiration as an essential part of the cumulative annual CO₂ efflux, whereas monitoring points inside the cities represent the gradient in mesoclimatic conditions driven by the urban heat island effect as well as the age and management of urban soils.