The influence of green roof features on their carbon and nutrient stocks
摘要
Extensive green roofs can mitigate the adverse effects of urban nature loss by providing ecosystem services, such as biodiversity increase, stormwater management and temperature regulation. They also sequester carbon, retain nutrients and potentially improve urban air and rainwater quality. This study examined how roof age, substrate depth, fertilization and vegetation type affect carbon, nitrogen and phosphorus substrate stocks, as well as two nitrogen fluxes (mineralization and nitrification). We hypothesized that vegetation type (Sedum-only vs. diverse vegetation), substrate depth and fertilization would be the main drivers of these stocks and fluxes. Twelve extensive green roofs in three cities in Flanders, Belgium, were sampled across four seasons. Results suggest limited carbon sequestration potential. Roofs with diverse vegetation, particularly those with mosses and herbs, had higher total carbon and nitrogen substrate stocks. Carbon stocks ranged from 1400 to 2880 g m− 2 (mean: 1600 g m− 2) in diverse roofs, compared to 700–1050 g m− 2 (mean: 860 g m− 2; p < 0.001) in species-poor roofs. Nitrogen stocks ranged from 62 to 100 g m− 2 (mean: 83 g m− 2) in diverse roofs and between 38 and 60 g m− 2 (mean: 50 g m− 2; p < 0.001) in species-poor roofs. Fertilization had no significant effect, while substrate depth only influenced phosphorus substrate stocks (p = 0.012). Overall, extensive green roofs offer limited carbon sequestration and nutrient retention. However, optimizing substrate composition and increasing plant diversity could enhance these benefits. This study highlights the potential for improving green roof performance through better design and management.