Seasonal dynamics of carbon, nitrogen, and phosphorus stoichiometric traits in an extensive green roof in Nanjing, China

Green roofs (GRs) are vital for shaping the material cycles of urban ecosystems as a form of distributed green infrastructure. However, current studies have predominantly focused on the material exchange between GRs and the urban environment, neglecting the internal distribution and equilibrium of constituent elements. By monitoring carbon (C), nitrogen (N), and phosphorus (P) in Sedum lineare Thunb and four substrates throughout the seasons, this study analyzes the ecological stoichiometric characteristics of an extensive GR in Nanjing, China. Intra-annual ratios of C:N (46.02, 13.38, 15.40), C:P (252.41, 57.85, 47.22), and N:P (5.75, 4.23, 3.84) were identified in the plant, substrate, and substrate microbial biomass, respectively. The intra-annual ratios of plant to substrate C, N, and P were roughly 9:1, 7:3, and 6:4, respectively. The use of different substrates resulted in significant variations in plant C, N, and P levels and their quantitative ratios, leading to distribution differences of these elements. Furthermore, substrate C, N, and P levels exhibit a generalized threshold effect on microbial biomass and plant C, N, and P concentrations. Notably, the substrate demonstrates an organic C sink potential of 7.11 g/kg/season, surpassing that of plants in unit mass. These findings contribute to understanding the distribution and dynamics of C, N, and P elements within extensive GRs.