Green roofs

an increasingly visible component of urban environments

are becoming increasingly popular in many countries and have attracted much attention in China. The interest for green roofs has been related to their benefit as the crucial determinants of energy flux and of buildings water retention

so as to reduce stormwater runoff volumes and peak flows

mitigate effect of urban heat island and also provide urban habitats to improve urban biodiversity. However

there is rare research focusing on its carbon sequestration potential and the mitigation of climate change. In present study

two experiments were conducted on 10 green roofs with the objective of evaluating carbon accumulation potential of green roofs and the factors that affect green roof carbon storage. In the chamber experiment

a green roof was able to absorb CO

2

as high as 0.46 g per m

2

in one hour

and CO

2

concentration declined as much as 162×10

-6

over 5 minutes. Mean decrease of CO

2

concentration and CO

2

exchange rate in the chamber over the measurement period were 77.8×10

-6

and-0.24 g·m

-2

·h

-1



respectively. However

there was a high degree of variability because the photosynthesis rate of green roof plant greatly is dependent on light intensity and temperature

which change from time to time. Decrease of CO

2

concentrations ranged from 23.50×10

-6

to 162.00×10

-6

and CO

2

exchange rates ranged from-0.06 to-0.46 g·m

-2

·h

-1

in the chamber. In the aboveground harvest experiment

data of the carbon reserve investigations showed that these green roofs stored an average of 92.55 g·m

-2

in aboveground biomass with also a wide variability(from 39.47 to 138.41 g·m

-2

)

depended on the harvested biomass and carbon content of the biomass collected from the studied green roofs. In addition

it is notable that a significant correlation (R

2

=0.93) was observed between plant carbon content and substrate depth

while the correlations between substrate nutrient variables and carbon content was not statistically significant. Overall

the experimental results suggested that green roof can reduce the CO

2

concentration in surrounding environment by absorbing CO

2

in the daytime and act as a small carbon sink in urban area. It is likely that substrate depth may have big impacts on green roof carbon sequestration potential. Additional sophisticated research should be needed to evaluate the factors that contribute to the carbon sequestration potential of green roofs.