| Green roof has the ecological function of mitigating the heat island effect,reducing the energy consumption of urban buildings,retention and purification of rainwater,and is one of the important urban green infrastructures.In the megacities where the land is limited,green roof has gradually become the main way to increase green in the city.However,there are few studies on the regulation effects of green roof plants on building temperature and rainwater retention and purification.The only research is limited to Sedum lineare.This paper selects two kinds of crassulacean acid metabolism plants(Sedum lineare and Callisia repens),two C3 turfgrasses(Poa pratensis and Festuca arundinacea)and two C4+C3 turfgrass combinations [Lolium perenne(winter)+ Cynodon dactylon(summer),Agrostis stolonifera(winter)+ Eremochloa ophiuroides(summer)] as the research object,discussed the regulation effect of different green roof plants on the temperature of the four-season roof,plant evapotranspiration and substrate moisture,the relationship between rainwater runoff and irrigation and the purification of rainwater runoff by different green roof plants.The main results are as follows:(1)Green roof significantly regulated roof temperature.In summer,all green roofs had a significant cooling effect.The cooling effect of the C4 turfgrassess on the canopy were significantly better than that of the C3 turfgrasses and crassulacean acid metabolism(CAM)plants had the worst cooling effect on the canopy,and all green roofs can significantly reduce the temperature of the substrate layer compared to the control.In winter,green roof had a heat preservation effect,and turfgrasses had a better thermal insulation effect on the substrate than CAM plants,and the heat preservation effect of the Agrostis stolonifera and Poa pratensis was the best.(2)The evapotranspiration of the green roof determines the water dynamics of the culture substrate,the runoff of the rainwater and the demand for irrigation by the plants.The greater the evapotranspiration was,the faster the soil water content decreased,and the interception effect on rainwater is also different.Green roofs significantly increased evapotranspiration,the two C4+C3 turfgrasses had the highest annual evapotranspiration and the two CAM plants had the lowest annual evapotranspiration.Green roofs significantly reduced runoff,the two CAM plants had the most annual runoff and the Agrostis stolonifera +Eremochloa ophiuroides green roof had the smallest annual runoff.Different evapotranspiration resulted in different irrigation.There were significant differences in the annual irrigation amount of different green roofs,the two CAM plants did not need irrigation for the whole year,C3 plants were significantly higher than C4 plants.(3)The difference in water and nutrient absorption and metabolism by greening plants is the main determinant of green roof on storm water runoff quantity and quality.When the rainfall was 5mm/d and 10mm/d,no runoff was generated in each green roof.There was no significant difference in the runoff between the two C4 turfgrasses(Cynodon dactylon and Eremochloa ophiuroides)and the two C3 turfgrasses(Poa pratensis and Festuca arundinacea)at rainfall of 25 mm/d and above,different runoff generated in different green roofs.The two kinds of CAM plants(Sedum lineare and Callisia repens)had the highest runoff,and there were no significant difference in C3 and C4 plants.Green roof significantly improved the quality of rainwater compared to control.C4 plants and C3 plants had a better performance in NH4-N,NO3-N,TN,PO4-P,TP,COD and SS than CAM plants,Among them,the purification effect of Eremochloa ophiuroides in C4 plants is better,and the purification effect of Festuca arundinacea in C3 plants is poor. |
