Soil salinization significantly impacts the ecological environment and agricultural production, posing a threat to plant growth. Currently, there are over 400 varieties of Bougainvillea with horticultural value internationally. However, research on the differences in salt tolerance among Bougainvillea varieties is still insufficient. Therefore, this study aims to investigate the physiological responses and tolerance differences of various Bougainvillea varieties under different concentrations of salt stress, reveal the effects of salt stress on their growth and physiology, and study the adaptation mechanisms of these varieties related to salt stress. The experimental materials consisted of five varieties of Bougainvillea. Based on the actual salinity concentrations in natural saline-alkali soils, we used a pot-controlled salt method for the experiment, with four treatment concentrations set: 0.0% (w/v) (CK), 0.2% (w/v), 0.4% (w/v), and 0.6% (w/v). After the Bougainvillea plants grew stably, salt stress was applied and the growth, physiology, and salt tolerance of the one-year-old plants were systematically measured and assessed. The key findings were as follows: Salt stress inhibited the growth and biomass of the five varieties of Bougainvillea; the ‘Dayezi’ variety showed severe salt damage, while the ‘Shuihong’ variety exhibited minimal response. As the salt concentration and duration of salt stress increase, the trends of the changes in antioxidant enzyme activity and osmotic regulation systems in the leaves of the five Bougainvillea species differ. Membrane permeability and the production of membrane oxidative products showed an upward trend with stress severity. The salt tolerance of the five varieties of Bougainvillea was comprehensively evaluated through principal component analysis. It was found that the ‘Shuihong’ variety exhibited the highest salt tolerance, followed by the ‘Lvyehuanghua’, ‘Xiaoyezi’, ‘Tazi’, and ‘Dayezi’ varieties. Therefore, Bougainvillea ‘Shuihong’, ‘Lvyehuanghua’, and ‘Xiaoyezi’ are recommended for extensive cultivation in saline-alkali areas. The investigation focuses primarily on how Bougainvillea varieties respond to salt stress from the perspectives of growth and physiological levels. Future research could explore the molecular mechanisms behind the responses to and tolerance of different Bougainvillea varieties as to salt stress, providing a more comprehensive understanding and basis for practical applications.

Leaf functional traits are an important part of plant adaptive strategies and respond differently to different environments, but our understanding of how plants adapt to highly complex urban environments through coordinated changes in leaf functional traits is limited. In order to deeply explore the effects of different urban environments on the leaf functional traits of landscape plants, this study focused on ten common landscape plants in Nanjing, specifically, Euonymus japonicus, Pittosporum tobira, Loropetalum chinense, Photinia × fraseri, Acer palmatum, Euonymus japonicus ‘Aurea-marginatus’, Platanus acerifolia, Camphora officinarum, Ginkgo biloba, and Lagerstroemia indica. The study employed one-way analysis of variance (ANOVA), two-way ANOVA, principal component analysis (PCA), and membership function comprehensive evaluation to explore the responses of green space plants to the environments of urban park green spaces (PAR), urban community green spaces (NL), and urban road green spaces (CR) and to analyze the impact of the trade-off strategies of plants in different green space environments based on leaf functional traits. The results showed that plant leaf functional traits and their adaptive strategies varied in different urban environments in Nanjing. The contents of LDMC, MDA, POD, and CAT in the ten plant species followed the order CR > NL > PAR, and SLA, SOD, SS, and total chlorophyll showed trends of PAR > NL > CR. The microstructures of the leaves of the ten plant species, such as SA, TUE, and TS, were evident in the expression of adaptive adjustments to the different green space environments. The principal component analysis and the comprehensive evaluation of the affiliation function of the indicators of the ten plant species revealed that the adaptability of the ten green space plants to the complex urban environment was as follows: Euonymus japonicus ‘Aurea-marginatus’ > Lagerstroemia indica > Acer palmatum > Photinia × fraseri > Platanus acerifolia> Camphora officinarum > Loropetalum chinense > Ginkgo biloba > Euonymus japonicus > Pittosporum tobira. The results of the study will help to further understand the layout, application, and maintenance of landscape plants in the context of urbanization and provide support for related theories.