Temperature and soil moisture control CO2 flux and CH4 oxidation in urban ecosystems

Climate-driven shifts in soil temperature and soil moisture are crucial factors that control the ecosystem-atmosphere greenhouse gas (GHG) balance. In the present study, the relationship between CO₂, CH₄ fluxes and soil moisture content and temperature sensitivity was examined in three dominating types of urban ecosystems: grassland, city park and arable land. The analysis was based on the field measurements at biweekly intervals over a year using a static closed chamber method in Wroclaw urban area, Poland. The observed patterns of land-atmosphere CO₂ and CH₄ exchange varied across land cover types and were strongly influenced by seasonal variations in temperature and soil water content. Emission of CO₂ from grassland and the city park was two times higher than from the arable land. The calculated CH₄ oxidation rate was one and half times higher (p < 0.05) under grassland and the city park as compared to arable land.

The estimated Q₁₀ values ranged between 1.68 and 1.79 for CO₂ and from 1.26 to 1.49 for CH₄, depending on the ecosystem type. The temperature sensitivity of soil respiration decreased when the temperature was above 24.5 °C across the moisture gradient from 20 to 25 % m/v. Results suggest that despite the urban areas with agricultural land use revealed the lowest CO₂ fluxes compared to grassland and city park, the former showed the lowest seasonal mean CH₄ oxidation. This indicates that with ongoing warming, the higher Q₁₀ of CO₂ production vs. CH₄ oxidation will further shift the carbon balance towards the source and this shift will be especially critical for arable lands in urban areas.