Change of nutrients, microorganisms, and physical properties of exposed extensive green roof substrate

Green roofs (GR) can be used as a nature-based solution to tackle eco-environmental problems caused by climate change and rapid urbanization. The substrate in the GRs is the growing medium for vegetation, and its properties directly affect the ecosystem services of GRs. To investigate the characteristic changes of an exposed substrate after the removal of vegetation, a one-year field experiment was conducted. Substrate properties were comprehensively compared for areas in GR that were planted with Sedum lineare and those with bare substrate. Results show that vegetation cover not only prevented substrate loss by 5.14% (p < 0.05) but also protected the chemical, microbial, and physical properties of the substrate. Moreover, the structure of the substrate changed, as evidenced by a significant increase in fine sand (p < 0.05). The results highlight that attention should be paid to maintaining vegetation cover during GR management. In addition, extensive GRs may not be suitable for fallowing. Once a GR has been established, it needs regular maintenance. Otherwise, the ecological and economic benefits of the GR may be reduced. The findings of the present study can be used to determine the life-cycle costs. Further research should focus on differences in the substrate loss rates, runoff, and temperatures of the substrates under exposure and vegetation cover. The microbial changes after revegetation should also be studied to clarify the role of vegetation in GR ecosystems. The present study provides a reference for improving GR management and ensuring their sustainability.