Soil bacterial diversity is associated with human population density in urban greenspaces

Urban greenspaces form a vital part of the urban ecosystem and provide an extensive array of ecosystem services, including pollutant degradation, water management, carbon maintenance, and nutrient cycling. However, while the soil microbiota in these ecosystems are essential to these services they remain under-characterized. Here we aimed to determine whether turf grass soil bacterial communities were associated with human population density across a range of greenspaces in parks, streets, and residential areas across a major urban area. Results showed that bacterial diversity was significantly positively correlated with population density within the immediate vicinity of the sampled areas; and species diversity was greater in park and street soils, when compared with residential zones. Population density and greenspace type (park vs street vs residential area) also associated with the composition and structure of the bacterial community. Edaphic properties, including pH, moisture and texture, were also significantly correlated with microbial composition and structure. Co-occurrence network analysis revealed that microbial guilds in urban soils were well connected. Soil moisture and texture together with population density and greenspace type showed strong correlations with several network topological features including assortativity degree, edge density, average path, average betweenness and closeness. These results indicate that changes in urban demographics, as well as the changes in land-use may influence the diversity and structure of urban soil microbial communities. As urbanization is rapidly growing across the planet, understanding the consequences of different urban zoning on soil microbiota represents an unmet need.城市绿地是城市生态系统的重要组成部分，可提供种类繁多的生态系统服务，包括污染物降解、水文管理、碳维持以及养分循环。不过，尽管此类生态系统中的土壤微生物群（soil microbiota）对这些服务至关重要，但其特征仍未得到充分解析。本研究旨在探究某大型城市区域内公园、街道与居住区等各类绿地中的草坪草土壤细菌群落，是否与采样区域周边的人口密度存在关联。结果显示，采样区域周边的细菌多样性与人口密度呈显著正相关；与居住区土壤相比，公园与街道土壤的物种多样性更高。人口密度及绿地类型（公园、街道与居住区）同样与细菌群落的组成与结构显著相关。土壤理化性质（edaphic properties），包括酸碱度、湿度与土壤质地，也与微生物群落的组成及结构存在显著关联。共现网络分析（co-occurrence network analysis）结果表明，城市土壤中的微生物功能群（microbial guilds）连接紧密。土壤湿度、土壤质地，结合人口密度与绿地类型，与多项网络拓扑特征（network topological features）存在强相关，包括同配性程度、边密度、平均路径长度、平均介数与亲近中心性。上述结果表明，城市人口统计特征的变化，以及土地利用方式的改变，均可能影响城市土壤微生物群落的多样性与结构。当前全球城市化进程快速推进，明确不同城市分区对土壤微生物群的影响，仍是一项尚未得到满足的研究需求。