北京城市绿地表层土壤碳氮分布特征研究

Abstract

Urbanized land cover and urban populations in China both have increased markedly since 1980 s. The rapid and massive urbanization has resulted in widespread ecological and environmental consequences from local to regional and national scales. To alleviate the negative impacts of urbanization and make our cities more sustainable,it is important to understand how urbanization affects biogeochemical cycles,particularly C and N dynamics. So far,however,understanding of urban soil biogeochemistry is rather limited,and more research is urgently needed. In this study,we collected 490 topsoil samples( 0—20cm) from different types of green space in urban and suburban area within the sixth-ring road range of Beijing,China. We analyzed concentration and density of soil organic carbon( SOC),inorganic carbon( SIC),total carbon( TC),and total nitrogen( TN),in order to explore the characteristics of the spatial distribution of carbon and nitrogen in the top layer of urban soils. The results showed that urban soils had higher SOC and SIC contents than suburban soils,and soil carbon content varied significantly between different land uses. The roadside tree pit soils had significantly higher SOC,SIC and TC density than other land-use type,and differences in SOC content among other types were not significant. SIC densities of residential,institutional,parks and transportation soil were significantly higher than those of suburban forests,nurseries,and orchards. For urban sites,roadside tree pit had highest SOC,SIC,and TC density,whereas park had lowest SOC,SIC,and TC. The difference in SOC between different land use were not significant. For suburban sites,roadside tree pit also had the highest SOC,SIC,and TC. The differences in SOC and TC among other land cover types were not significant. Shelterbelt and productive plantations had lower SIC densities than other land cover types throughout the entire metropolitan. Comparing similar land cover types between urban and suburban sites,institutional and transportation had significant higher SOC than the same types in the suburban sites. Yet urban parks and roadside tree pits had slightly lower SOC than the similar types in the suburban area. Urban land cover types had higher SIC and TC than the same land cover types of the suburban sites. Significantly negative correlations existed among SOC,SIC and TC,as well as between these variables and distance from the urban core. In other words,SOC,SIC,and TC tended to decrease with increasing distance away from the urban core. This indicates that urbanization in Beijing has augmented the local soil carbon pool to some extent. No significant differences in soil TN were found between land cover types or between urban and suburban sites. But TN and C / N tended to decrease along the urban-rural gradient. Further studies are needed to clarify the effects of urbanization on soil nitrogen in the Beijing region.