The impact of amendments on the microbial community response in green roof substrate layers

Currently, extensive research has focused on optimizing the materials of the matrix layer in green roofs to enhance their performance, while studies on the impact of green roof improvements on microorganisms remain limited, despite the critical role of microorganisms in facility longevity and environmental sustainability. This study simulated rainfall in a city in China, applied different amendments, and analyzed the nitrogen and phosphorus pollution characteristics of the substrate layer of green roofs composed of zeolite and peat soil, as well as the response of microbial communities in the substrate. The results indicated that Polyacrylamide (PAM) led to leaching of total nitrogen (TN); while Polyaluminium chloride (PAC), Aluminum sulfate (AS), and Polymeric ferrous sulfate (PFS) all exhibited retention effects on TN, with PFS demonstrating the greatest TN reduction effect. The three amendments of PAC, AS, and PFS all showed good reduction efficiency for total phosphorus (TP). In terms of microbial community response, the application of PAC, AS, and PFS led to a significant decrease in α-diversity in the substrate layer, while the PAM group showed slightly higher α-diversity compared to the control group. The five phyla with the highest abundance were Proteobacteria, Actinobacteriota, Chloroflexi, Bacteroidota and Acidobacteriota. After the experiment, the microbial diversity of the PAC, AS, PFS groups increased, whereas the microbial diversity of the control group (CK) and the PAM group decreased. Based on the development trends of microbial community diversity and structure, it was found that the PAC, AS, and PFS treatment groups not only exhibited resistance to continuous rainfall conditions but also adapted to the stress of nitrogen and phosphorus pollution in the substrate layer.