Soil CO2 Fluxes in an Urban Green Space: A Case Study during the Northern Portuguese Spring Season

Abstract

Globally cities account for more than 70% of CO₂ emissions. The potential of urban green spaces as a biotechnology to reduce the net emissions is influenced by the type of vegetation and soil management. Thus, appropriate management of urban soils plays an important role in mitigating climate change, as it affects the biological processes responsible for carbon loss or gain in the soil. The knowledge about the carbon (C) sequestration capacity of grass soils in urban green spaces is still incipient. The study of soil CO₂ fluxes is essential to implement more appropriate forms of mitigation in the management of areas with this type of ground vegetation cover. Therefore, this study aimed at investigating CO₂ fluxes in a lawn area located in the city of Bragança. CO₂ fluxes were measured continuously at a sampling interval of 30 minutes (total number of samples 5523) using the LI-8100A system from LI-COR Biosciences^®, together with monitoring of edaphoclimatic and vegetative parameters, during the last month of winter and the tree months of spring. The results showed the importance of herbaceous vegetation in reducing CO₂ emissions compared to those that would result from bare soil. However, throughout the observation period, the lawn surface acted as an emitting source with an average magnitude of 1.25 ± 5.31 g C m^-2 d^-1. The study allowed the identification of phytovolume and soil water availability as the most determining factors in this complex process that underlies the vertical fluxes that occurring at the surface/atmosphere interface. In this sense, management practices related to the frequency and amount of water used in irrigation, as well as the height and frequency of vegetation cutting were identified as key factors on the net exchange of CO₂ on these lawn surfaces.