Substrate microorganisms can be an ideal tool for improving green roof sustainability

Green roof (GR) ecosystems function as a result of a series of complex interactions between plants and substrates, which are poorly understood. This ambiguity hinders the scientific application of GRs to tackle urban eco-environmental problems. The goal of this study was to clarify the response of plants to various abiotic and biotic characteristics of GR substrates, including physical properties, nutrients, and microbes. We systematically analyzed the statistical association between 43 indicators of plant and substrate characteristics using four GR substrates and one common plant type (Sedum lineare Thunb) in a subtropical monsoon climate. Height, coverage, root-shoot ratio, total carbon, total nitrogen, total phosphorus, total potassium, root vitality, and malondialdehyde levels were considered sensitive indicators of the plant's response to the substrate. Substrate nutrients and microbial biomass were most closely associated with the plant response, whereas the material properties of the substrate could indirectly affect plant growth by influencing substrate microbes and plant nutrients. Our results suggest that when optimizing GR substrates for plant responses, it is necessary to respect the plants and account for the abiotic and biotic relationships. It may be possible to manage GR performance in a more scientific and effective manner through the control of substrate microorganisms.