快速城市化地区昆明市“城—郊—乡”梯度土壤表 层碳氮磷化学计量特征

基于航空遥感影像,利用地理信息系统(ArcGIS 10.2)和景观格局分析(Fragstats 4.2)软件,通过主成分分析(PCA)和多元线性回归分析对研究区城市化水平进行量化,选取覆盖研究区典型的“城—郊—乡”样带,进行表层土壤取样,测定总有机碳(C)、全氮(N)、全磷(P)的含量并分析其空间变化特征。结果表明:快速的城市化进程导致了土壤C、N、P化学计量特征的空间分异,“城—郊—乡”梯度上变异系数都较大,尤其城区各元素的变异系数分别为84.08%、76.95%和81.34%,属于强变异,表明土壤表层C、N、P含量空间分布极不均衡。研究区土壤C、N、P含量均表现为城区显著高于郊区的特征,与郊区土壤相比,城区土壤C含量较高,说明人为活动造成城区土壤明显的有机质富集现象。城区土壤P含量高于郊区和乡村,城市化过程加剧了城区土壤P的富集,也使该地区水体(主要是滇池)面临富营养化风险。分析城市化过程中强烈的人类活动干扰对土壤C、N、P含量及其化学计量特征,对于提高城市土壤管理水平、改善生态环境、促进城市生态系统健康持续发展具有重要意义。今后昆明市在进行城市绿化时可有针对性地选择部分豆科固氮植物加强生物固氮,目的是提高土壤N含量的同时促进城区土壤丰富的P被吸收利用,在一定程度上预防以及减轻P对水体的危害。

Stoichiometric characteristics of topsoil C,N and P along urban-suburbrural gradient in a rapid urbanizing area of Kunming

Rapid urbanization is associated with physical changes in the landscape,such as increasingly impervious surface area and the replacement of natural vegetation with lawns,which can positively or negatively alter soil organic carbon(SOC)stocks.Based on remote sensing image,geographic information system(ArcGIS 10.2)and landscape pattern analysis software(Fragstats 4.2),regional urbanization levels were analyzed using principal component analysis(PCA)and multiple linear regression in the central Kunming.Then soil sampling plots were selected from typical sites based on the urban-suburb-rural gradient covering the central Kunming,and stoichiometric variability of topsoil C,N and P was analyzed.The results indicated that the spatial differentiation of soil C:N:P characteristic is caused by the rapid urbanization process.The coefficient of variation(CV)in the urban area is the highest.The CV for each element in the urban area is 84.08%,76.95% and 81.34%,respectively,indicating that the spatial distribution of C,N and P contents in the soil surface is extremely uneven.The content of C,N and P in the topsoil is significantly higher in the urban area than in the suburbs.Compared with the soil in the suburbs,the content of C in the urban area is higher,indicating that human activities have caused obvious organic matter enrichment in the urban area.The content of topsoil P in urban areas is higher than that in the suburbs and rural areas.The urbanization process aggravates the enrichment of topsoil P in urban areas,and also exposes the water bodies(mainly Dianchi Lake)to the risk of eutrophication.The analysis of soil C,N and P contents and stoichiometric characteristics caused by human activities in the process of urbanization is of great significance for improving the level of urban soil management,improving the ecological environment and promoting the healthy and sustainable development of urban ecosystem.In the future,some leguminous nitrogen fixation plants can be selected in Kunming for urban greening to strengthen biological nitrogen fixation.The purpose is to improve soil N content and promote the absorption and utilization of P in urban soil,so as to prevent and reduce the harm of P to water.