Research On The Carbon Balance Of Dominant Species In Urban Green Space Based On Life Cycle Assessment ——A Case Study Of Tianjin,china

Urban green space carbon cycle is a very important link in the process of urban carbon cycle.Plants fix carbon dioxide in their bodies through photosynthesis.At the same time,due to the consumption of resources and labor-input during the construction and maintenance process,carbon dioxide will be produced and released back into the atmosphere.With the improvement of the status of China’s ecological civilization construction,the construction of low-carbon cities has increasingly drawn a lot of people’s attention.As the only green infrastructure in a city that reflects the function of carbon sinks,urban green space is of great significance in achieving the task of carbon emission reduction in the city.In the process of urbanization at home and abroad,urban green space is generally regarded as an important carbon sink in a city.However,most studies often regard urban green space as a net carbon sink and ignore its carbon emissions.In fact,in the process of urban green space construction,management and maintenance,due to the inadaptability of the planting situation and the irrationality of the management model,the carbon emission level of urban green space will become higher and higher,even exceeding the amount of carbon sequestration.Throughout the life cycle,various inputs and expenditures involve carbon emissions,which will make urban green spaces carbon source.Taking the dominant species in different types of urban green spaces in Tianjin as the research object,we select typical urban green space samples,calculate the carbon sequestration and carbon emissions in their life cycle by combining on-site investigation and data review,and evaluate different types of green space.This paper analyzes the carbon balance of green space in different types of cities,discusses the influence of different factors on the level of carbon budget,and then puts forward the irrationality of the current green space planning and the room for improvement,and provides suggestions for the construction and planning of low-carbon cities in the future.Some conclusions had been drawn in the paper as that:（1）The order of carbon sequestration of trees from high to low is: Populus tomentosa,Fraxinus chinensis,Paulownia fortunei（Seem.）Hemsl,Salix babylonica,Platanus orientalis,Acer mono Maxim,Robinia pseudoacacia L,Sophora japonica.The order of carbon sequestration of shrubs from high to low is: Prunus cerasifera,Lonicera maackii,Malus micromalus,Buxus megistophylla Levl.（2）The carbon emissions in construction and maintenance are different in different types of urban green space,irrigation and fertilization produce the most carbon emissions.（3）Most plants have carbon source and sink turning points.The net carbon sequestration of Acer mono Maxim and Robinia pseudoacacia L was negative in the first 10 years,and the carbon balance of Sophora japonica was changed from source to sink after 20 years.After 26 years,it has changed from carbon source to carbon sink as for Malus micromalus.The lawn is always a carbon source.（4）Type,age and density of plants will affect carbon sequestration,and there is still a large space for carbon reduction in the current conservation model of urban green space.（5）Carbon sequestration benefits of China’s urban green space have obvious step distribution characteristics;the built-up area of municipal districts,urban construction land area,per capita GDP,population,and urban green space carbon sequestration are all correlated with the carbon sequestration.