城市化对绿地土壤团聚体稳定性及有机碳含量的影响:以江西省南昌市为例

Impacts of Urbanization on Soil Aggregate Stability and Organic Carbon Content in Urban Greenspaces:A Case Study of Nanchang City,Jiangxi Province

探究城市化对土壤团聚体稳定性和土壤有机碳(SOC)含量的影响机制,将有助于城市绿地土壤质量改善.以江西省南昌市建成区为例,按不透水率区分城市化强度,实地调查和测定184个绿地样方植被特征及其土壤性质,分析不同城市化强度土壤团聚体组分(>2、1~2、0.25~1、0.053~0.25和<0.053 mm)的稳定性指标(几何平均直径、平均重量直径、分形维数以及不稳定团粒指数)和SOC含量差异及其与土壤理化性质和植被特征之间的相互作用机制.结果表明:①低城市化区域0.053~0.25 mm团聚体质量分数显著低于中、高城市化区域(P<0.05);而土壤团聚体稳定性指标在不同城市化强度区域无显著性差异(P>0.05).②低城市化区域中>2、1~2、0.25~1和0.053~0.25 mm团聚体SOC含量显著高于高城市化区域26%~39%(P<0.05),而<0.053 mm团聚体SOC则不受城市化影响(P>0.05).③冗余分析和结构方程模型共同表明城市化影响土壤理化性质(降低全氮、全磷和提高容重)变化,进而间接降低团聚体中SOC积累;而较大的树高、胸径、冠幅、多样性指数和草本植物盖度则能直接或间接增加团聚体SOC含量,提高土壤团聚体稳定性.综上所述,城市化虽然可以间接降低团聚体SOC含量,但并不影响团聚体稳定性,调节土壤理化性质和植被特征指标变化可以缓解城市化对土壤团聚体SOC积累产生的负面影响,为城市绿地土壤质量提升提供理论依据.

Exploring the mechanisms of the impacts of urbanization on soil aggregate stability and soil organic carbon(SOC)content will contribute to improving soil quality in urban greenspaces.Using the built-up area of Nanchang City,Jiangxi Province as a case study,the urbanization intensity was differentiated by impervious rate,and the vegetation characteristics and soil properties of 184 greenspace plots were investigated and determined.Variations in the stability parameters(geometric mean diameter,mean weight diameter,fractal dimension,and unstable aggregate index)and SOC contents across soil aggregate-size fractions(>2,1-2,0.25-1,0.053-0.25,and<0.053 mm)and their interaction mechanisms with soil physicochemical properties and vegetation characteristics were analyzed in different urbanization intensities.The results showed that:①The mass fractions of 0.053-0.25 mm aggregates in low urbanization areas were significantly lower than that in medium and high urbanization areas(P<0.05),whereas there was no significant difference in soil aggregate stability among different urbanization intensities(P>0.05).②The SOC contents of>2,1-2,0.25-1,and 0.053-0.25 mm aggregates were significantly higher than that in high urbanization areas by 26%-39%(P<0.05),while the SOC contents of<0.053 mm aggregates were not affected by urbanization(P>0.05).③Both redundancy analysis and structural equation modeling demonstrated that urbanization influenced the changes in soil physicochemical properties(decreasing total nitrogen and phosphorus and increasing bulk density),which indirectly reduced SOC accumulation of aggregates,whereas the larger tree height,diameter at breast height,crown diameter,diversity index,and herb coverage could directly or indirectly improve SOC content and the stability of aggregates.In conclusion,although urbanization indirectly decreased the SOC contents of aggregates,the aggregate stability was not affected by it.The manipulation of soil physicochemical properties and vegetation characteristics could alleviate the negative effects of urbanization on the SOC accumulation of aggregates,which provides a theoretical foundation for improving soil quality in urban greenspaces.