Articles
Assessment of atmospheric CO2 reduction and water use efficiency of C3, C4 and CAM plants in an extensive green roof under drought stress
Article number
1429_28
Pages
233 – 242
Language
English
Abstract
Urban green roofs provide a number of ecosystem services including atmospheric CO2 reduction and urban-heat island effect mitigation.
However, in semi-arid regions such as the eastern Mediterranean, water scarcity is a major issue and brings the water use efficiency (WUE) of plants used in green roofs to the fore.
Succulents (CAM photosynthetic plants) are internationally the most used species on green roofs, mainly due to their low water requirements.
This work examines the question of whether, under severe drought, CAM plants contribute to atmospheric CO2 reduction compared to C4 plants and drought-tolerant C3 plants and compares plant species of the three photosynthetic types under drought conditions based on biomass production and WUE. The CAM species Sedum sediforme and Mesembryanthemum cordifolium, C4 species Atriplex halimus and Muhlenbergia capillaris and C3 drought-tolerant Mediterranean species Pallenis maritima and Cistus × purpureus ‘Alan Fradd’, were grown in a simulated green roof in a greenhouse in Athens, in boxes (5 plants of the same species per box) with a green roof infrastructure installed, in 10 cm deep substrate (grape marc compost:perlite:pumice, 3:3:4, v/v). Regular and sparse irrigation was applied immediately after installation, with min substrate moisture 17-20% and 8-11% v/v, respectively.
CAMs had the highest WUE followed by C4 plants, while C3 plants, especially P. maritima, showed the lowest WUE and required more water supply throughout the experimental period. Ιn CAMs, only M. cordifolium had a positive day-night CO2 balance, while S. sediforme appeared to emit a significant amount of CO2 during the day, which was not compensated by the CO2 absorbed at night. S. sediforme, P. maritima and M. capillaris were the least efficient in removing CO2 from the environment compared to the other species of the same photosynthesis type.
Thus, to improve carbon sequestration by green roofs, especially in the Mediterranean and other semi-arid climates, plant species that exhibit higher performance in removing CO2 from the atmosphere should be considered for use in extensive green roofs.
However, in semi-arid regions such as the eastern Mediterranean, water scarcity is a major issue and brings the water use efficiency (WUE) of plants used in green roofs to the fore.
Succulents (CAM photosynthetic plants) are internationally the most used species on green roofs, mainly due to their low water requirements.
This work examines the question of whether, under severe drought, CAM plants contribute to atmospheric CO2 reduction compared to C4 plants and drought-tolerant C3 plants and compares plant species of the three photosynthetic types under drought conditions based on biomass production and WUE. The CAM species Sedum sediforme and Mesembryanthemum cordifolium, C4 species Atriplex halimus and Muhlenbergia capillaris and C3 drought-tolerant Mediterranean species Pallenis maritima and Cistus × purpureus ‘Alan Fradd’, were grown in a simulated green roof in a greenhouse in Athens, in boxes (5 plants of the same species per box) with a green roof infrastructure installed, in 10 cm deep substrate (grape marc compost:perlite:pumice, 3:3:4, v/v). Regular and sparse irrigation was applied immediately after installation, with min substrate moisture 17-20% and 8-11% v/v, respectively.
CAMs had the highest WUE followed by C4 plants, while C3 plants, especially P. maritima, showed the lowest WUE and required more water supply throughout the experimental period. Ιn CAMs, only M. cordifolium had a positive day-night CO2 balance, while S. sediforme appeared to emit a significant amount of CO2 during the day, which was not compensated by the CO2 absorbed at night. S. sediforme, P. maritima and M. capillaris were the least efficient in removing CO2 from the environment compared to the other species of the same photosynthesis type.
Thus, to improve carbon sequestration by green roofs, especially in the Mediterranean and other semi-arid climates, plant species that exhibit higher performance in removing CO2 from the atmosphere should be considered for use in extensive green roofs.
Authors
M. Papafotiou, M. Trigka, G. Liakopoulos, A. Koutsardakis, P. Dariveris, D. Karagianni
Keywords
carbon sequestration, irrigation, Mediterranean native plant, semi-arid area, succulents, photosynthesis type, urban CO2, urban green roof, water stress
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