Diversity or standardization: CO2 emission from universal and locally specific green roof constructions along a climatic gradient

Purpose: Green roofs are promoted as nature-based solutions for urban climate mitigation, yet their net carbon sequestration potential across contrasting climates remains poorly constrained. Methods: We quantified July–September CO₂ emissions and carbon (C) balances of extensive green roofs during the first season after construction and identified key climatic and design drivers. Roofs were established along a climatic gradient in Russia (Ekaterinburg, Moscow, Rostov-on-Don) using universal (15 cm) and local substrates (15 and 25 cm), planted with Sedum (on shallow substrates only) and native herbaceous communities (on both substrate depths). All treatments were replicated three times giving a total of 18 roof plots per city. CO₂ was measured twice a month using dynamic closed chambers; substrate temperature and moisture were monitored continuously. Results: Mean CO₂ emissions ranged from 3.47 ± 1.51 g C m⁻² day⁻¹ in Ekaterinburg to 7.65 ± 5.39 g C m⁻² day⁻¹ in Moscow and 7.13 ± 6.53 g C m⁻² day⁻¹ in Rostov-on-Don. Seasonal dynamics in Ekaterinburg and Moscow were controlled by temperature (Q₁₀= 2.86–3.44), while moisture dominated in Rostov-on-Don. Substrate type was the main driver, with compost-enriched universal substrates emitting more CO₂ than local substrates; substrate depth had a city-dependent effect, while plant community had no influence on emissions. Across all sites, CO₂ emissions exceeded plant C uptake into aboveground biomass, indicating that most systems were net C sources during the first growing season. Higher biomass on universal substrates did not translate into greater C sequestration due to elevated emissions. Conclusions: Thus, climate-specific design is important to optimize green roof carbon performance.