High respiration rates induce net CO2 emissions in an urban allotment garden in Finland

Abstract

The carbon balance in urban allotment gardens remains poorly quantified. We assessed the carbon dioxide (CO₂) balance in an allotment garden in southern Finland using the eddy covariance method (EC) and soil chamber measurements. The year-round EC measurement showed that despite of 77 % vegetation cover, this ecosystem functioned as a net CO₂ source (0.69 kg m⁻²yr⁻¹). This resulted from high respiratory emissions (4.7 kg m⁻²yr⁻¹) exceeding substantial photosynthetic uptake (4.0 kg m⁻²yr⁻¹). This respiratory surplus was likely linked to elevated soil organic carbon (13.4 ± 8.7 %) and high soil C:N ratio originating from management amendments. While vegetation density enhanced photosynthesis in certain sectors within the garden, proportionally high respiration in the same sectors cancelled out any major net carbon uptake differences across the garden. These case-specific findings challenge assumptions about urban gardens as inherent carbon sinks and highlight that carbon-smart management practices may be needed to enhance carbon uptake and reduce emissions in urban gardens.