Archaea rather than bacteria govern green roofs greenhouse gas production

Urban air quality can be improved through a variety of strategies, one of which is to increase the amount of urban vegetation. In cities where there is insufficient ground space for increased vegetation, roof space can be utilised to establish green roofs that help to mitigate harmful gas content in air. This study uses the closed static chamber method to determine the scale of greenhouse gas (GHG) fluxes from three green roof types: Sedum mat roofs (three sites), lightweight clay aggregate (LECA)-based roofs (four sites), and Gramineae sod roofs (six sites). GHG fluxes from these sites were also compared with those from a flat roof lawn garden and a natural control area. Our results highlight the importance of soil-based archaea in affecting all GHGs from green roofs. Mat and LECA roofs had similar carbon dioxide (CO₂) fluxes, but CO₂ flux from sod roofs was strongly affected by substrate composition. Furthermore, CO₂ flux had a similar seasonal variation across all study sites, with the lowest fluxes in May and September, and the highest fluxes in June, July and August. The main process involving methane (CH₄) on green roofs was oxidation, with sod roofs having stronger oxidation levels than either mat or LECA roofs. This was further confirmed by microbial data on methanogens and methanotrophs. There was no significant nitrous oxide (N₂O) flux from any of the study sites. According to the results, we conclude that non-fertilised green roofs are not significant sources of GHGs and will rather help to mitigate GHG levels in urban areas, like Gramineae-based roofs may be used effectively for CH₄ consumption.