Under the background of global climate change and China’s “carbon peak and carbon neutrality” strategy, it is of great significance to assess the carbon sink benefits of urban park plant communities. This study took 20 plant community plots of 20 m × 20 m (400 m²) in Tientsin Water Park as the research object. Carbon sequestration capacity was characterized by carbon stock (CS) and annual carbon sequestration (ACS), and six community structure indicators were quantified: Vegetation Coverage (VC), Canopy Density (CD), Three-Dimensional Green Volume (3DGV), Tree-to-Shrub Ratio (TSR), Vertical Complexity (CV), and Number of Individuals (N). Spearman correlation analysis, principal component analysis, and regression analysis were adopted, and K-means clustering was introduced to identify vegetation structure–function groups, thereby exploring the statistical correlations between these structural characteristic indicators and carbon sink capacity indicators (CS and ACS). The results showed that (1) VC, CD, and 3DGV were significantly positively correlated with CS, suggesting that these factors may be more conducive to long-term carbon pool accumulation; (2) N was significantly positively correlated with ACS, and a nonlinear decreasing trend was observed in the current observation data; (3) the influence of TSR and CV on carbon storage and sequestration also showed a nonlinear correlation. Based on the above correlation findings, the community combinations with higher carbon sink performance in this case were screened out. And suggestions for low-carbon configuration of plant communities, centered on optimizing canopy structure, configuring high-carbon-sequestration tree species, and regulating reasonable density, were proposed, which can be used as a reference for forming hypotheses in subsequent confirmatory studies.

Under global climate change and rapid urbanization, urban heat island and dry island effects threaten residents’ thermal comfort and public health, making microclimate regulation by urban green spaces a core issue. However, the interaction between vertical structure and horizontal spatial type of plant communities remains unclear. This study selected Tianjin Water Park as the study area. Based on field temperature and humidity observations during the high-temperature period in summer 2024, ENVI-met was locally validated and used for multi-scenario numerical simulations of typical plant communities. Results showed that all vegetation structure types had cooling and humidifying effects. Tree–shrub–herb communities showed the strongest cooling and humidifying performance, while shrub–herb communities showed the weakest performance (p < 0.05). A higher degree of horizontal enclosure was associated with more stable temperature and humidity conditions. For cooling, an interaction-dependent effect was found between vertical structure and horizontal spatial type: the cooling benefit of greater vertical structural complexity increased with the degree of enclosure. These findings clarify the independent and interactive mechanisms by which plant community structure regulates microclimate. They also provide a scientific basis and quantitative reference for optimizing plant arrangement in urban parks.