This study explored the soil arbuscular mycorrhizal (AM) fungal communities in park green spaces under the context of urbanization, aimed to provide foundational data support for the soil microbial diversity and ecological conservation of parks in Nanchang City.

In this study, three urbanization gradient levels (high, medium, and low) were divided according to the proportion of impervious surface area in the built-up area of Nanchang City, and 63 sample plots of park green space soil were sampled and investigated. High-throughput sequencing technology was used to detect the community characteristics of arbuscular mycorrhizal (AM) fungi in the soil, analyze the differences in the structural composition, Alpha diversity and Beta diversity of AM fungal communities, and reveal the correlation between AM fungal communities and soil physicochemical properties through RDA analysis.

The AM fungal communities in the park green spaces of Nanchang City were predominantly composed of dominant genera such as Glomus and Paraglomus. The Shannon and Simpson indices exhibited a significant logarithmic increase with rising urbanization intensity by 3.89% and 1.90%, whereas the Dominance index showed a significant logarithmic decrease by 44.36%. Soil pH value, electrical conductivity, soil organic carbon content and total nitrogen content were positively correlated with the abundance of genera such as Glomus, Claroideoglomus, Scutellospora and Gigaspora; total potassium content, moisture content and soil bulk density were positively correlated with the abundance of genera such as Archaeospora and Diversispora, and soil total phosphorus content was positively correlated with the abundance of genera such as Paraglomus.

With the increase in urbanization intensity, species diversity and community evenness of AM fungi communities increased, while the dominance of the dominant genera weakened. Soil physicochemical factors such as soil organic carbon, pH value, total phosphorus content, and total potassium content play a key role in influencing the composition of AM fungal communities.

To reveal the changes and spatial distribution characteristics of soil fertility in urban forest in Nanchang.

184 surface soil samples (0-20 cm) of different forest types (landscape forests, institution-affiliated forests, road forests and ecological forests) were took as the object in the built-up area of Nanchang city. Seven soil parameters including soil total nitrogen, total phosphorus, total potassium, available phosphorus, soil organic carbon, bulk density, pH were measured to provide an overall rating and factor analysis of soil fertility in Nanchang city. The modified Nemerow composite index method was used to comprehensively evaluate the soil fertility of different forest types in Nanchang city, and urban spatial distribution maps were drawn for each soil parameter using ArcGIS software. The status of the content level of each parameter was evaluated with reference to the classification standard (6-level system) developed by the Second National Soil Census.

Soil total phosphorus (0.69 mg·g^-1) and available phosphorus (23.86 mg·kg^-1), and their spatial distribution characteristics reached grade 3 or above, and their contents were in the middle to upper level; Soil organic carbon (16.76 mg·g^-1) and total nitrogen (0.90 mg·g^-1), and their spatial distribution characteristics reached grade 4, with contents at the lower middle level; Total potassium (9.70 mg·g^-1) and its spatial distribution characteristics reached grade 5, and the content was at a low level; The comprehensive soil fertility index of most areas in Nanchang was between 1.3 and 1.5, which was at a medium level (ranked 3rd in the 4-level system); Soils of different forest types showed that the highest comprehensive soil fertility index (1.32) was in landscape forests.

Among the soil fertility parameters in Nanchang urban forest, soil organic carbon, total nitrogen and total potassium are the main limiting factors; The spatial distribution of soil fertility in urban forests in Nanchang is characterized by high soil bulk density, neutral and acidic soil pH, scanty total nitrogen, total potassium and soil organic carbon, and abundant total phosphorus and available phosphorus, with available phosphorus up to the second level and above. In this study, the soil fertility of urban forest was comprehensively evaluated to provide theoretical basis for urban forest construction and conservation management, and give full play to urban forest ecological benefits in Nanchang.