Changes of forest topsoil carbon fractions across urban-rural transects in Beijing

Rapid urbanization has profoundly altered soil carbon cycling and thereby reshaped the spatial pattern of soil carbon content and fractions across the urban-rural gradients. In this study, we measured the contents of total carbon and its different fractions in the topsoil (surface layer 0-10 cm and subsurface layer 10-20 cm) of twenty parks across four urban-rural transects in Beijing, China. We analyzed the spatial variations of different soil carbon fractions and their potential driving factors across the urban-rural gradients. The results showed that topsoil total carbon (topsoil: 21.0 ± 1.6 g/kg; subsurface soil: 18.0 ± 1.3 g/kg) was dominated by organic carbon (topsoil: 64.6% ± 4.5%; subsurface soil: 54.9% ± 4.5%). Topsoil contents of organic carbon showed a nonlinear trend from the urban core to the rural area, while the topsoil inorganic carbon content decreased significantly. Topsoil organic carbon (topsoil: 13.8±1.5 g/kg; subsurface soil: 10.0±1.2 g/kg) was dominated by particulate organic carbon (topsoil: 71.3%± 2.4%; subsurface soil: 70.5% ± 2.9%). The contents of both particulate organic carbon and mineral associated organic carbon showed nonlinear changes across the urban- rural forest transects. The proportion of particulate organic carbon was relatively low in urban areas, while that of mineral associated organic carbon showed an opposite trend. Soil texture, soil pH, and park age were important drivers to shape the spatial variation of topsoil carbon components across the urban- rural transects, while the urban- rural climate gradient and species diversity were found to have an unimportant role. Our findings improve the understanding of how urbanization reshapes soil carbon fractions and have useful implications for soil management in urban forests. © 2024 Science Press. All rights reserved.