Abstract
Different vegetation types used for the extensive green roofs have characteristic physiological and morphological traits (e.g., C3, C4, or CAM photosynthesis, deciduous or evergreen). Several Sedum species are recognized as “inducible CAM” type plants. These differences in the physiological and morphological traits have a considerable effect on the carbon sequestration in the green roofs. The objective of the present study was to quantify the carbon sequestration in several green roof plants during the first year after the construction of the green roofs and to clarify the relevance of the physiological and morphological traits to each plant’s ability to sequester carbon in its body using the growth analysis method. We used Zoysia matrella , Ophiopogon japonicus , and Sedum mexicanum species for the study wherein, S. mexicanum was assigned to the wet, dry, and non-irrigation treatments, and Z. matrella and O. japonicus only received the wet treatment. During the first year after the construction, carbon sequestration in the plants and the substrate of S. mexicanum was in the range of 276 to 364 g-C/m2/year, which was similar to that of O. japonicus and the finding of a previous study. In contrast, Z. matrella exhibited the highest carbon sequestration (670 g-C/m2/year), which is also expressed as the relative plant C-sequestration rate per whole-plant C-content (RGRc), because Z. matrella is a C4 plant and exhibits the highest net assimilation rate (NARc) of all species. Significant differences were not observed in RGRc , NARc , and RMF (root mass fraction) in S. mexicanum between the wet and dry treatments. These results suggest that in countries with high rainfall, a high frequency of irrigation has an insignificant effect on the physiological and morphological characteristics, and carbon sequestration in the Sedum green roofs.
Highlights
Green roofs are considered an effective technology for solving urban environmental problems
The growth analysis is generally applied to the dry weight of the plant, we focused on the carbon content of the plant and calculated RGRc, NARc, and LARc
During the first year after the construction of the green roofs, carbon sequestration of the three species is represented as grams of carbon per m2 per year (Table 6) as Z. matrella: 670 g-C/m2/year, O. japonicus: 282 g-C/m2/year, S. mexicanum: 336 g-C/m2/year in the wet treatment, S. mexicanum in the dry and nonirrigation treatments was 364 and 276 g-C/m2/year, respectively
Summary
Green roofs are considered an effective technology for solving urban environmental problems. Some of their benefits include mitigation of the urban heatisland effect [1], cooling and insulation of buildings [2] [3], storm water management [4] [5], air pollution reduction [6], habitat provision for other organisms [7], and carbon sequestration [8] [9]. It was identified that the carbon content in rooftop lawns tends to increase for thirteen years and green roofs are considered a sink for carbon dioxide (CO2). These benefits arise from the presence of living plants and the growing medium. Carbon sequestration in green roofs has a direct relationship with the physiological and morphological traits of the vegetation because the plants sequester atmospheric CO2 through photosynthesis, fix carbon, and supply carbon through the litter and root exudates
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