Distribution Characteristics and Adaptation Mechanisms of Exotic Spontaneous Plant Diversity in Urban Road Green Spaces of Changchun, China

Spontaneous plants are plants that occur in urban environments such as pavement gaps or cracks in walls without cultivation and are not remnants of historic native habitats. They are critical components of urban road green space vegetation, and their distribution is affected by multiple factors. Heavy traffic and frequent human disturbances on urban roads exacerbate exotic spontaneous plant invasions. Exploring the diversity of their distributions, adaptation mechanisms of these exotic plants and their relationship with native ones is vital for focused control of harmful invasives. Based on field surveys, this study analyzed the distribution of exotic spontaneous plants across habitat types, urbanization gradients and disturbance intensities in road green spaces, and their interactions with native counterparts. Our results indicated: (1) 425 spontaneous species were recorded (234 exotic, 191 native), with 71.8% cosmopolitan and 74.7% monotypic genera. (2) The spontaneous exotic plant community achieves extensive resource preemption by forming a structure dominated by a single super-dominant species (Setaria viridis) and characterized by a broader overall niche breadth. (3) Different habitats sustain a similar number of exotic spontaneous plant species (i.e., α-diversity), but their species compositions are highly differentiated, with such differences driven almost entirely by species turnover. At the urban scale, spontaneous exotic plants adapt to regional environments with varying urbanization intensities by maintaining extensive similarity in community composition and making only extremely weak adjustments to the pattern of individual distribution among species. (4) The spontaneous plant community exhibits a pattern dominated by weak interspecific associations and random assemblages, where ecological interactions among species are weak, and the community structure is more consistent with the stochastic processes described by the Neutral Theory. At the regional environmental gradient scale, the diversity of spontaneous native and exotic plants exhibited coordinated variation. The study provides a scientific basis for urban biological invasion control and biodiversity management.