The role of soils in carbon sequestration by urban green infrastructures: a university campus case study

Urban green infrastructures (UGI) are considered among the main nature-based solutions to reach carbon (C) neutrality and support climate mitigation strategies in cities. City governments have high expectations from C sequestration by UGI, however, the role of soils remains overlooked. Lack of information on C stocks and fluxes in urban soils increases uncertainty in C accounting and probably overestimates the real potential for C sequestration. Soil organic carbon (SOC) stocks and CO2 emissions are highly variable in space and time. It is important to understand the factors driving this variability to support C-smart solutions in UGI planning and management. This study aimed to explore the effect of UGI typology and age on SOC stocks and soil respiration by using the Wageningen University campus as a living lab. The campus is dominated by lawns, herbaceous meadows, shrubs and trees with well-documented management practices. To study the
effect of time since construction, the vegetation was further classified according to their age. Overall, the topsoil SOC stocks were quite low (3.01 kg m-2). Soils under trees (3.27 kg m-2) and shrubs (3.14 kg m-2) had higher SOC stocks compared to lawns (2.93 kg m-2) and herbs (2.74 kg m-2). SOC stocks of recently constructed sites were higher compared to older ones. Carbon fractionation further determined the quality of the SOC stocks. Lawns showed the highest respiration rates indicating that lawns in urban greenspace are less favourable for climate change mitigation. Temperature sensitivity analysis of respiration indicated how the soils respond to increasing temperatures.