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

Abstract

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： ① The 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）. ② The 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）. ③ Both 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.