北京城市绿地表层土壤碳氮分布特征

在北京中心城区及周边郊区(覆盖六环路范围),采集不同类型绿地表层(0—20cm)土壤样品490份,测定了土壤有机碳、无机碳、全碳和全氮含量,探讨了城市土壤碳氮分布特征。结果表明:城市不同类型绿地土壤中碳含量差异明显,行道树土壤的有机碳、无机碳和全碳含量均显著高于其他类型绿地,而其它类型土壤有机碳含量差异不显著;居住绿地、道路绿地、单位绿地和公园绿地土壤无机碳含量显著高于生产绿地、防护绿地;城市土壤有机碳、无机碳和全碳含量与距离城市中心距离呈显著的负相关关系;与郊区土壤相比,城区绿地土壤有机碳、无机碳含量有富集的趋势,且无机碳增加更加明显;与郊区农业土壤相比,城市绿地土壤中有机碳有明显地增加趋势,说明北京的城市化在一定程度上有利于土壤碳库的累积。不同类型绿地土壤全氮含量差异不显著,城郊之间全氮含量也无显著差异,土壤全氮质量分数和碳氮比有逐渐减小的趋势,城市化对土壤氮的影响需要进一步研究。

Spatial distribution of soil carbon and nitrogen in urban greenspace of Beijing

Urbanized land cover and urban populations in China both have increased markedly since 1980s. 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 top-soil 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.