Spatial Pattern Characteristics And Driving Mechanism Of Soil Organic Carbon Storage In Shanghai Urban Green Space

The rapid urbanization has yielded cities of unprecedented size and form that considerably modify major biogeochemical cycles, especially the carbon cycle. Understanding the relationship between urban sprawl and the carbon cycle is of great importance to ensure sustainable urban planning and management. In this study, the major objective was to quantify the spatial pattern of soil organic carbon (SOC) density in Shanghai City, China, which has undergone rapid urban expansion and intense land-use change since the 1980s. We established 4 sampling transects radiating from the Shanghai urban core to the edge of the city. Soil sampling was conducted at 121 sites over green space along the 4 transects and each transect is composed of about 30 sites covering 7 different land-use types (business area, residential area, educational area, park green space, arterial road, industrial zone and agricultural area). Soils were sampled at 0-15cm,15-30cm and 30-50cm depths at each site between Oct.2013 and May.2014. Then the SOC density of each site was analyzed.The main conclusions are as follows:(1) The city-wide mean SOC density at 0-50 cm depth level of 121 sites is 7.408± 2.020 kg m-2, with significant spatial difference among the four transects in the order as: the South Transect (8.185±2.632 kg m-2)> the East Transect (7.525±1.456 kg m-2)> the West Transect (7.210±2.104 kg m-2)> the North Transect (6.760±1.478 kg m-2). The spatial distribution of SOC storage of transects is affected by the characteristics of the underlying surface in Shanghai city. There was no significant relationship between SOC density (mg cm-3) and the sampling plot’s distance from the urban core, with a slightly increasing trend.(2) Land use type or functional regionalization is a main factor that affecting the differences in SOC densities. Among all land use types, green space around commercial area shows the highest carbon storage, the average SOC density of commercial area is 7.951±1.832 kg m-2. However, green space around residential area has the lowest carbon storage,(averagely 6.310±2.140 kg m-2). The average SOC densities (in terms of numerical values) of the other 5 land uses are in the orders:green park (7.825±1.718 kg m-2)> agriculture district (7.724±1.485 kg m-2)> educational district (7.707±2.017 kg m-2)> arterial traffic (7.185±2.078 kg m-2)> industrial zone (6.869±2.128 kg m-2).(3) SOC content of Shanghai urban green space at 0-15 cm depth level was significantly greater than the other two layers (15-30 cm and 30-50 cm)., SOC contents of other sampling sites in various functional types decrease with soil depth, except the sites in the industrial zones. SOC densities of 0-15 cm and 30-50 cm depth levels are similar, and slightly higher than 15-30 cm soil layer. All kinds of land uses or functional zones are in accordance with this law.(4) Soil disturbance history is a potential factor that drives the spatial pattern of SOC storage of urban green space. Our results show that SOC densities of green parks are increasing with soil disturbance time. Green space soils in commercial areas show the same tendency as green parks. But there seems to be no correlation between soil forming history and SOC densities of green space soils in educational districts and residential areas.