Carbon sequestration potential of native grasses in extensive green roof systems

Green roofs are increasingly adopted as nature-based solutions to mitigate urban environmental impacts, including carbon storage. however, information on the performance of native grasses in green roofs conditions remains limited. This study evaluated growth dynamics and carbon sequestration potential of native ornamental grasses cultivated under extensive green roof. Eight genotypes were assessed, including accessions and cultivars of Paspalum notatum (BRA006513, BRA019178, BRA023558, Aruaí, Tiriba and Tuim), Axonopus parodii (Curica), and the exotic grass Zoysia japonica as a commercial reference. Plants were grown in trays with a 8 cm substrate depth and monitored over 365 days, with evaluations at 90, 180, 270 and 365 days after planting. Plant height, surface coverage, fresh biomass, dry mass, organic carbon concentration and carbon stocks were quantified in above- and belowground compartments. Biomass accumulation and carbon storage increased over time, with root systems becoming the main carbon sink after establishment. However, reductions in plant height and surface coverage were observed after intermediate periods, likely due to environmental and structural constraints of extensive green roofs, such as shallow substrate depth, limited rooting volume, and periodic water restriction, which induced physiological adjustments including reduced vertical growth and canopy senescence. At 365 days, accession BRA023558 showed higher root carbon concentration than Z. japonica, while BRA019178 exhibited consistently greater carbon stock, including higher aboveground accumulation at 270 days. Overall, native grasses performed similarly or better than the exotic reference species, with BRA019178 and BRA023558 showing the greatest potential for biomass development and carbon accumulation under extensive green roof conditions.