| Roof greening is the hot spot of urban greening at the present stage.It is not restricted by the urban environment and topography,and the development momentum is very rapid,which has a very positive significance for the improvement of urban environment.In May 2018-2019,this study during October,box-type method and volume method is used respectively to ecological system of zhengzhou city roof greening,the total carbon storage of CO2 flux and its related biological and environmental factors in the long-term monitoring of high density,analyzed thedifferent time scales on the roof greening ecosystem respiration(ER),total ecosystem productivity(GEP),net ecosystem exchange capacity(NEE)between changes in the characteristics and the relationship between environmental factors,in order to reduce the uncertainty of the ecosystem carbon balance,explore the carbon cycle dynamic and response mechanism between the environmental factors,The dynamic change trend of the future carbon cycle is forecasted,and then the contribution of the roof greening ecosystem to the environment at the carbon sink level is evaluated,and the scientific basis is provided for the optimal management of the roof greening.The results show that:(1)the average temperature in the growing season of the roof greening ecosystem in 2018(may-october 2018)was 25.1℃,slightly higher than the atmospheric temperature in the growing season of 2019(may-october 2019,24.8℃),with the lowest temperature reaching-3.5℃ at the end of December;The annual change trend of atmospheric pressure in the study area is opposite to that of temperature.It is high in winter and low in summer,presenting a u-shaped change trend.The 2019 growing season received more rain than the 2018 growing season,with total rainfall of 545.6mm and 479.1mm,respectively,while the 2018-2019 non-growing season(from November 2018 to April 2019)received very little rain,with total rainfall of only 88.4mm.The overall trend of solar radiation observation data throughout the year is a single peak state,taking the season as the time scale,and ranking in the order from high to low according to the values:summer,autumn,spring and winter,it reached the highest value(30.93 MJ·-2d-1)in June 2018,and the lowest value(3.34 MJ·m-2d-1)in December.(2)during the period from November 2018 to February 2019,the roof greening ecosystem of zhengzhou presents as a carbon source,and the maximum value of NEP is-0.32g C m2(December 2018).Growing season in 2018 and 2019 growing season,2018-2019 growing season are characterized by carbon sinks,the NEP(total ecosystem productivity)were 185.5 m2,344.7 m2 g C and 17.4 g C g C m2,fully evaluated the total ecosystem productivity is 2390.7 m2 g C,ecosystem respiration totaling 1808.4 m2 g C,the whole period of the efficiency of carbon sequestration(ECSE)was 22.9%,and two growing season and is characterized by strong carbon sink function.(3)in this study,the daily variation curve of NEE of the roof greening ecosystem is asymmetrically distributed.In the growing season,the curve is bimodal,with a short "siesta"phenomenon,while in the n on-growing season,the curve is unimodal.The maximum value of NEE is around 9:00 in October 2019,which is-14.30±0.504 mol CO2 m2s-1.The change trend of GEP and NEE in each month is synchronous;ER presented a single peak curve in the whole period,with a maximum value of 10.28±0.305 mol CO2 m2s-1(15:00),and the time was July 2019.(4)environmental factors affect NEE by affecting ecosystem photosynthesis and respiration.The regression equations were yER=0.277e0.096x(R2=0.623)and yGEP=0.058e0.145x(R2=0.338),and the temperature sensitivity coefficient of ecosystem respiration(Q10)was 2.614.There was a quadratic function change between the partial pressure of water vapor and ER and GEP,and the correlation was significant.R2 was 0.473 and 0.290,respectively,but the two had different adaptability to the excessive partial pressure of water vapor,which reached the threshold at 30 kPa and 35 kPa respectively.The correlation between evapotranspiration and GEP(R2=0.465)was higher than that between evapotranspiration and ER(R2=0.352).When the evapotranspiration was greater than 1.8 nmol H2O,m-2 s-1 would restrict the photosynthesis,and ER was not affected by it.(5)the maximum organic carbon density of roof greening soil,overground and underground plants in CBD of zhengzhou city was measured by carbon accumulation method as 1071.8g/m2(rg-13),453.3g/m2(rg-2)and 4.8g/m2(rg-13),respectively.The total reserves of organic carbon were respectively 46.91t,13.13t and 2.50t,and the organic carbon was mainly stored in the soil. |
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