Biological　nitrogen　fixation　(BNF)　is　an　important　source　of　nitrogen　in　ecosystems.　Compared　to　symbiotic　nitrogen-fixing　microorganisms,　free-living　diazotrophic　bacteria　have　a　broader　distribution　and　greater　diversity,　demonstrating　greater　potential　for　application.　Leaf　surfaces　constitute　one　of　the　largest　microbial　reservoirs　on　Earth,　harboring　a　variety　of　free-living　diazotrophic　bacteria,　contributing　significantly　to　plant　N　acquisition　and　growth.　The　distribution　patterns,　abundance,　diversity,　and　the　environmental　variables　affecting　the　asymbiotic　nitrogen　fixation　(ANF)　rates　of　free-living　diazotrophic　bacteria　of　non-leguminous　plants　in　urban　green　spaces　were　investigated　using　high-throughput　sequencing　of　nifH　gene　amplicons　and　the　acetylene　reduction　method.　Both　green　space　type　and　plant　species　significantly　impact　ANF　rates　and　nifH　gene　abundance　in　the　phyllosphere,　with　green　space　type　having　a　more　pronounced　effect.　Leaf　metal　elements　iron　(Fe),　molybdenum　(Mo),　and　the　free-living　diazotrophic　bacteria　of　the　genus　Skermanella　collectively　influence　the　ANF　rates　in　the　phyllosphere　of　urban　green　spaces.　Linear　regression　analysis　revealed　that　metal　elements　Fe,　Mo,　and　potassium　(K)　in　the　leaves　were　significantly　positive　correlated　with　the　diversity　of　the　free-living　diazotrophic　bacteria　and　the　abundance　of　the　N-fixing　gene　nifH.　The　alpha　diversity　and　symbiotic　network　structure　of　the　free-living　diazotrophic　bacterial　community　in　the　phyllosphere　indicated　a　significant　negative　correlation　between　human　disturbance　and　environmental　perturbation　and　the　biodiversity　and　network　complexity　of　these　bacteria.　This　study　provides　a　crucial　foundation　for　understanding　the　nitrogen-fixing　functions　of　microbes　in　urban　ecosystems　and　their　contributions　to　the　nitrogen　cycle.　©　The　Author(s),　under　exclusive　licence　to　Springer　Science+Business　Media,　LLC,　part　of　Springer　Nature　2025.